April 21, 2021, 15:34 PDT

NASA Technologies Spin off to Fight Climate Change

By Mike DiCicco,
NASA’s Spinoff Publication

An orbital sunrise is pictured from the International Space Station (ISS) as it orbited 260 miles (418 kilometers) above the Pacific Ocean, about 500 miles (805 kilometers) southwest of Mexico. As Earth's climate changes, the ISS watches from above, helping to provide unique insights to keep our planet safe. Credit: NASA

An orbital sunrise is pictured from the International Space Station (ISS) as it orbited 260 miles (418 kilometers) above the Pacific Ocean, about 500 miles (805 kilometers) southwest of Mexico. As Earth's climate changes, the ISS watches from above, helping to provide unique insights to keep our planet safe. Credit: NASA

NASA’s work has generated countless spinoffs that are now on the front lines of the fight against climate change. That shouldn’t be a surprise, since the agency’s missions include studying Earth and improving aircraft efficiency.

But that’s not the only way NASA’s innovations make an impact. Many advances to meet the harsh demands of space travel are also helping to reduce greenhouse gases, improve alternative energy sources, and increase our understanding of the causes and effects of climate change.

Read on for a few examples, and head over to spinoff.nasa.gov/climate-change for a roundup of dozens more.

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Trapping Greenhouse Gases

Carbon dioxide, a greenhouse gas, is the most prominent driver of climate change on Earth. On Mars, however, where most of the atmosphere is CO2, the gas could come in handy. Under NASA contracts, one engineer helped develop technology to capture Martian carbon dioxide and break it into carbon and oxygen for other uses, from life support to fuel for a journey home.

Although it never flew, Perseverance will test out a similar idea, using an experimental system called MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment). Meanwhile, the earlier technology led to a system that now captures natural gases at oil wells, instead of wastefully burning them off and dumping the resulting CO2 into the atmosphere.

And another version of the system helps beer breweries go “greener” by capturing carbon dioxide from the brewing process, rather than venting it, and using it for carbonation instead of buying more.

Conserving Energy

Conserving energy is a crucial consideration for space travel, and many innovations NASA has come up with in that arena are now widespread in improving energy efficiency on Earth.

For example, NASA helped create a type of reflective insulation to efficiently maintain a comfortable temperature within spacecraft and spacesuits. In the decades since, this insulation has been adapted and used in homes and buildings around the world.

Another material pioneered to insulate cryogenic rocket fuel against the balmy weather around the launch pad at Cape Canaveral, Florida, now saves energy by preserving temperatures at industrial facilities. And a coating invented to protect spacecraft during the extreme heat of atmospheric entry improves the efficiency of incinerators, boilers, and refractories, ovens, and more.

Infographic: More NASA Tech Helping to Solve Climate Challenges
NASA research and innovations have led to many environment-saving spinoffs, and this graphic highlights a few. Credit: NASA
Click for PDF version

Shrinking Air Travel’s Carbon Footprint

Air travel is a major contributor to human-made greenhouse gases. Designing aircraft to fly more efficiently reduces the amount of fuel they burn, and in turn, their resulting emissions. And many of the improvements that make modern aircraft more efficient come straight from NASA.

In fact, some of the agency’s most significant contributions to aeronautic fuel efficiency can be traced back to the work of a single NASA engineer in the 1960s and ’70s. Richard Whitcomb designed and tested an entirely new wing shape – the supercritical wing – that significantly increased efficiency at high speeds and eliminated weight.

He then designed upturned wingtips that make use of air vortices that would otherwise create drag. Now incorporated into nearly all commercial planes, these advances combined save billions of dollars’ worth of fuel, along with associated CO2 emissions, every year.

In the decades since, NASA has continued to work with industry partners to improve airplane efficiency, and the agency is now supporting the cutting edge of all-electric flight.

Advancing Renewable Energy

Because there are no fossil fuels on Mars, NASA became interested in wind energy to power future Martian operations. So, the space agency helped a company develop a wind turbine that could operate in a similarly harsh environment – the South Pole. Rugged and designed for easy maintenance and efficiency at extremely low temperatures, more than 800 of the resulting turbines are now generating power on Earth.

Unexpectedly, software NASA supported for improved aircraft design and maintenance has also led to more efficient, long-lasting wind turbines. And several solar panel manufacturers have benefited from the agency’s long reliance on the sun for energy.

Understanding Climate Change

Mountains of data from a fleet of Earth-observing NASA satellites help countless other agencies, researchers, and companies better understand the causes and effects of climate change. The agency has worked with commercial partners to make this data manageable and easier to mine for information. Other companies have benefited from NASA’s support for technology to monitor conditions on the ground and in the oceans and atmosphere, including innovative devices to sense local greenhouse gases and ocean conditions. The resulting data helps to verify and enrich the agency’s models of Earth weather and climate, which span decades, circle the globe, and peer into the future.

NASA has a long history of transferring technology to the private sector. The agency’s Spinoff publication profiles NASA technologies that have transformed into commercial products and services, demonstrating the broader benefits of America’s investment in its space program. Spinoff is a publication of the Technology Transfer program in NASA’s Space Technology Mission Directorate.

For more information on how NASA brings space technology down to Earth, visit:

spinoff.nasa.gov

March 25, 2021, 07:45 PDT

The Raw Truth on Global Temperature Records

From old buckets to high-tech buoys: why initial temperature data need to be adjusted

By Alan Buis,
NASA's Jet Propulsion Laboratory

Weather stations are set up throughout Glacier National Park in Montana to monitor and collect weather data. These stations must be visited periodically for maintenance and to add or remove new research devices. Credit: GlacierNPS, CC BY 2.0, via Wikimedia Commons

Weather stations are set up throughout Glacier National Park in Montana to monitor and collect weather data. These stations must be visited periodically for maintenance and to add or remove new research devices. Credit: GlacierNPS, CC BY 2.0, via Wikimedia Commons

Ensuring the accuracy of Earth’s long-term global and regional surface temperature records is a challenging, constantly evolving undertaking.

There are lots of reasons for this, including changes in the availability of data, technological advancements in how land and sea surface temperatures are measured, the growth of urban areas, and changes to where and when temperature data are collected, to name just a few. Over time, these changes can lead to measurement inconsistencies that affect temperature data records.

Scientists have been building estimates of Earth’s average global temperature for more than a century, using temperature records from weather stations. But before 1880, there just wasn’t enough data to make accurate calculations, resulting in uncertainties in these older records. Fortunately, consistent temperature estimates made by paleoclimatologists (scientists who study Earth’s past climate using environmental clues like ice cores and tree rings) provide scientists with context for understanding today’s observed warming of Earth’s climate, which has no historic parallel.

Over the past 140 years, we’ve literally gone from making some temperature measurements by hand to using sophisticated satellite technology. Today’s temperature data come from many sources, including more than 32,000 land weather stations, weather balloons, radar, ships and buoys, satellites, and volunteer weather watchers.

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To account for all of these changes and ensure a consistent, accurate record of our planet’s temperature variations, scientists use information from many sources to make adjustments before incorporating and absorbing temperature data into analyses of regional or global surface temperatures. This allows them to make “apples to apples” comparisons.

Let’s look more closely at why these adjustments are made.

To begin with, some temperature data are gathered by humans. As all of us know, humans can make occasional mistakes in recording and transcribing observations. So, a first step in processing temperature data is to perform quality control to identify and eliminate any erroneous data caused by such errors – things like missing a minus sign, misreading an instrument, etc.

Changes to Land Weather Stations

A NOAA Automated Surface Observing System (ASOS) weather station
A NOAA Automated Surface Observing System (ASOS) weather station at the Childress Municipal Airport in Childress, Texas. ASOS stations constantly monitor weather conditions on Earth’s surface. More than 900 stations across the United States report data about sky conditions, surface visibility, precipitation, temperature and wind up to 12 times an hour. Credit: NOAA

Next are changes to land weather stations. Temperature readings at weather stations can be affected by the physical location of the station, by what’s happening around it, and even by the time of day that readings are made.

For example, if a weather station is located at the bottom of a mountain and a new station is built on the same mountain but at a higher location, the changes in latitude and elevation could affect the station’s readings. If you simply averaged the old and new data sets, the station’s overall temperature readings would be lower beginning when the new station opens. Similarly, if a station is moved away from a city center to a less developed location like an airport, cooler readings may result, while if the land around a weather station becomes more developed, readings might get warmer. Such differences are caused by how ground surfaces in different environments absorb and retain heat.

Then there are changes to the way that stations collect temperature data. Old technologies become outdated or instrumentation simply wears out and is replaced. Using new equipment with slightly different characteristics can affect temperature measurements.

Data adjustments may also be required if there are changes to the time of day that observations are made. If, for example, a network of weather stations adopts a uniform observation time, as they did in the United States, stations making such a switch will see their data affected, because temperature is dependent on time of day.

Scientists also make adjustments to account for station temperature data that are significantly higher or lower than that of nearby stations. Such out-of-the-ordinary temperature readings typically have absolutely nothing to do with climate change but are instead due to some human-produced change that causes the station readings to be out of line with neighboring stations. By comparing data with surrounding stations, scientists can identify abnormal station measurements and ensure that they don’t skew overall regional or global temperature estimates.

In addition, since the number of land weather stations is increasing over time, forming more dense networks that increase the accuracy of temperature estimates in those regions, scientists also take those improvements into account so data from areas with dense networks can be appropriately compared with data from areas with less dense networks.

Changes to Sea Surface Temperature Measurements

Much like the trends on land, sea surface temperature measurement practices have also changed significantly.

Wooden bucket used to measure sea surface temperatures during World War II.
Wooden bucket used to measure sea surface temperatures during World War II. Credit: The Mariners’ Museum

Before about 1940, the most common method for measuring sea surface temperature was to throw a bucket attached to a rope overboard from a ship, haul it back up, and read the water temperature. The method was far from perfect. Depending on the air temperature, the water temperature could change as the bucket was pulled from the water.

During the 1930s and ‘40s, scientists began measuring the temperature of ocean water piped in to cool ship engines. This method was more accurate. The impact on long-term ocean surface temperature records was to reduce the warming trend in global ocean temperatures that had been observed before that time. That’s because temperature readings from water drawn up in buckets prior to measurement are, on average, a few tenths of a degree Celsius cooler than readings of water obtained at the level of the ocean in a ship’s intake valves.

Schematic of a typical engine cooling water intake system on a modern merchant vessel
Schematic of a typical engine cooling water intake system on a modern merchant vessel. From the 1930s to around 1990, scientists measured sea surface temperatures by measuring the temperature of ocean water piped in to cool ship engines. Credit: Robin Matthews / CC BY 4.0

Then, beginning around 1990, measurements from thousands of floating buoys began replacing ship-based measurements as the commonly accepted standard. Today, such buoys provide about 80% of ocean temperature data. Temperatures recorded by buoys are slightly lower than those obtained from ship engine room water intakes for two reasons. First, buoys sample water that is slightly deeper, and therefore cooler, than water samples obtained from ships. Second, the process of passing water samples through a ship’s inlet can slightly heat the water. To compensate for the addition of cooler water temperature data from buoys to the warmer temperature data obtained from ships, ocean temperatures from buoys in recent years have been adjusted slightly upward to be consistent with ship measurements.

A NOAA National Data Buoy Center buoy
A NOAA National Data Buoy Center buoy off the coast of Newport, Oregon. Buoys such as this one collect a wide variety of atmospheric and ocean data. Credit: NOAA

So Many Climate Data Sets, So Little Disagreement

Currently, there are multiple independent climate research organizations around the world that maintain long-term data sets of global land and ocean temperatures. Among the best known are those produced by NASA, the National Oceanic and Atmospheric Administration (NOAA), the U.K. Meteorological Office's Hadley Centre/Climatic Research Unit (CRU) of the University of East Anglia, and Berkeley Earth, a California-based non-profit.

Comparison of four independent methods for estimating global temperature anomalies: NASA GISTEMP, NOAA NCEI, Hadley Centre/Climatic Research Unit (UK) and Berkeley Earth
Comparison of four independent methods for estimating global temperature anomalies: NASA GISTEMP, NOAA NCEI, Hadley Centre/Climatic Research Unit (UK) and Berkeley Earth. Despite differences in methodologies used by these independent researchers, their global temperature estimates are all in close agreement. Credit: Gavin Schmidt

Each organization uses different techniques to make its estimates and adjusts its input data sets to compensate for changes in observing conditions, using data processing methods described in peer-reviewed literature.

Remarkably, despite the differences in methodologies used by these independent researchers, their global temperature estimates are all in close agreement. Moreover, they also match up closely to independent data sets derived from satellites and weather forecast models.

NASA’s GISTEMP Analysis

One of the leading data sets used to conduct global surface temperature analyses is the NASA Goddard Institute for Space Studies (GISS) surface temperature analysis, known as GISTEMP.

GISTEMP uses a statistical method that produces a consistent estimated temperature anomaly series from 1880 to the present. A “temperature anomaly” is a calculation of how much colder or warmer a measured temperature is at a given weather station compared to an average value for that location and time, which is calculated over a 30-year reference period (1951-1980). The current version of GISTEMP includes adjusted average monthly data from the latest version of the NOAA/National Centers for Environmental Information (NCEI) Global Historical Climatology Network analysis and its Extended Reconstructed Sea Surface Temperature data.

GISTEMP uses an automated process to flag abnormal records that don’t appear to be accurate. Scientists then perform manual inspections on the suspect data.

Graph showing both adjusted and unadjusted temperature data
When all adjustments for non-climatic effects are incorporated into the land and ocean temperature input data NASA GISTEMP uses to estimate global temperature anomalies, the impact is to reduce the historical global temperature trends for the full 20th century. Credit: Gavin Schmidt

GISTEMP also adjusts to account for the effects of urban heat islands, which are differences in temperatures between urban and rural areas.

The procedure used to calculate GISTEMP hasn’t changed significantly since the mid-1980s, except to better account for data from urban areas. While the growing availability of better data has led to adjustments in GISTEMP’s regional temperature averages, the adjustments haven’t impacted GISTEMP’s global averages significantly.

While raw data from an individual station are never adjusted, any station showing abnormal data resulting from changes in measurement method, its immediate surroundings, or apparent errors, is compared to reference data from neighboring stations that have similar climate conditions in order to identify and remove abnormal data before they are input into the GISTEMP method. While such data adjustments can substantially impact some individual stations and small regions, they barely change any global average temperature trends.

In addition, results from global climate models are not used at any stage in the GISTEMP process, so comparisons between GISTEMP and model projections are valid. All data used by GISTEMP are in the public domain, and all code used is available for independent verification.

The Bottom Line

Independent analyses conclude the impact of station temperature data adjustments is not very large. Upward adjustments of global temperature readings before 1950 have, in total, slightly reduced century-scale global temperature trends. Since 1950, however, adjustments to input data have slightly increased the rate of global warming recorded by the temperature record by less than 0.1 degree Celsius (less than 0.2 degrees Fahrenheit).

A final note: while adjustments are applied to station temperature data being used in global analyses, the raw data from these stations never changes unless better archived data become available. When global temperature data are processed, the original records are preserved and are available to anyone who wants them, at no cost, online. For example, the NOAA National Climatic Data Center's U.S. and global records may be accessed here.

February 22, 2021, 11:21 PST

The Climate Connections of a Record Fire Year in the U.S. West

By Alan Buis,
NASA's Jet Propulsion Laboratory

Smoke from wildfires shrouded the San Francisco Bay Area and blocked sunlight on September 9, 2020. Credit: Aaron Maizlish/Flickr/CC BY 2.0

Smoke from wildfires shrouded the San Francisco Bay Area and blocked sunlight on September 9, 2020. Credit: Aaron Maizlish/Flickr/CC BY 2.0

The year 2020 will be remembered for many things, not the least of which were a series of devastating fires around the globe that bear the fingerprints of climate change. From Australia and South America’s Amazon and Pantanal regions, to Siberia and the U.S. West, wildfires set new records and made news year-round.

It was an especially bad year for wildfires on the U.S. West Coast. Five of California’s 10 largest wildfires on record happened in 2020, and the state set a new record for acres burned. According to CAL FIRE, the state’s Department of Forestry and Fire Protection, more than 9,600 wildfires burned nearly 4.2 million acres through mid-December, causing more than 30 fatalities and damaging or destroying nearly 10,500 structures.

Smoke from numerous wildfires obscures much of California and Oregon.
Smoke from numerous wildfires obscures much of California and Oregon in this image taken by the NOAA/NASA GOES-17 satellite on September 9, 2020. Credit: NOAA

The Golden State wasn’t alone. Oregon, Washington, and Colorado were also particularly hard hit. In fact, as of mid-December 2020, the National Interagency Fire Center reported more than 10.6 million acres burned and nearly 17,800 buildings destroyed across its seven geographic area coordination centers in the western half of the contiguous United States.

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The CZU lightning complex fire burns along Butano Ridge and in Pescadero Creek Park in California's Santa Cruz Mountains.
The CZU lightning complex fire burns along Butano Ridge and in Pescadero Creek Park in California’s Santa Cruz Mountains, August 19, 2020. The fire would later grow to more than 86,000 acres and destroy nearly 1,500 structures. Credit: Inklein, CC BY-SA 4.0, via Wikimedia Commons

It was the fire equivalent of a perfect storm. Record drought conditions across the Western United States in late 2019 extended into early 2020, and were followed by the hottest summer on record in the Northern Hemisphere. Add in unusually dry air, strong wind events, and an outbreak of summer thunderstorms in Northern California in August, and conditions were ripe for a dangerous fire season.

Natasha Stavros is an applied science system engineer at NASA’s Jet Propulsion Laboratory in Southern California who studies wildfires. She says that not only is the U.S. West experiencing more frequent wildfires, but they’re also happening at the same time, putting a strain on resources. They’re also bigger, more severe, and faster than ever before, and more destructive, with 15 of the 20 most destructive wildfires in California history occurring within the past decade.

Trends in the annual number of large fires in the western United States for a variety of ecoregions from 1984-2011.
Trends in the annual number of large fires in the western United States for a variety of ecoregions from 1984-2011. The black lines are fitted trend lines. The center map illustrates ecoregions based on Levels II and III of the Omernik ecoregion system. The Wyoming Basin and Colorado Plateau ecoregions had too few large fires for trend analysis at the ecoregion level, and are shown in gray. Monitoring Trends in Burn Severity-mapped fires are shown in red. Credit: Dennison, P. E., Brewer, S. C., Arnold, J. D., & Moritz, M. A. (2014). Large wildfire trends in the western United States, 1984–2011. Geophysical Research Letters, 41, 2928–2933. https://doi.org/10.1002/2014GL059576

Stavros attributes these trends to three primary factors: a changing climate, greater availability of fuel, and the expansion of urban areas, which brings with it more ignitions.

Climate Change: A Powerful Catalyst

“Climate affects how long, how hot and how dry fire seasons are,” she said. “As climate warms, we’re seeing a long-term drying and warming of both air and vegetation.”

Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for California.
Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for California. Observed data are for 1900–2014. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions). Temperatures in California (orange line) have risen about 2 degrees Fahrenheit since the beginning of the 20th century. Shading indicates the range of annual temperatures from the set of models.

Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected during the 21st century. Less warming is expected under a lower emissions future (the coldest years being about 2 degrees Fahrenheit warmer than the historical average; green shading) and more warming under a higher emissions future (the hottest years being about 9 degrees Fahrenheit warmer than the hottest year in the historical record; red shading). Credit: CICS-NC and NOAA NCEI

In recent decades, the U.S. West has warmed, and the frequency and severity of heat waves and droughts has increased. According to the National Oceanic and Atmospheric Administration (NOAA), temperatures in California have increased approximately 2 degrees Fahrenheit (1.1 degrees Celsius) since the beginning of the 20th century. This has dried out the air. Fire seasons are also starting earlier and ending later each year, while snow packs are shrinking, leading to earlier spring snowmelt and longer, more intense dry seasons.

These warmer and drier conditions are also making U.S. Western wildfires more severe. Another recent study led by Sean Parks of the U.S. Forest Service finds the amount of Western U.S. land burned by “high-severity” wildfires (fires that destroy more than 95 percent of trees) has increased 800 percent since 1985.

More Fuel to Burn

Another factor driving changes in U.S. Western wildfires is a greater availability of fuel. Drier air stresses vegetation, making forests more susceptible to severe wildfires, while droughts are creating more dead fuel. But, as Stavros explains, there are limits.

The Apple Fire burns into the night north of Beaumont, California, on Friday, July 31, 2020.
The Apple Fire burns into the night north of Beaumont, California, on Friday, July 31, 2020. Credit: Brody Hessin, CC BY 4.0, via Wikimedia Commons

“Fire is both fuel- and flammability-limited,” she said. “Take the state of Washington. You have lots of trees, but it tends to be really wet and cold there, so fires are limited by the flammability of the fuels. In a place like Nevada, however, the amount of fuel is limited, but it tends to be dry. Droughts increase fires in flammability-limited areas, but don’t have an impact in fuel-limited areas. Ironically, you have to have rain to have a fire.”

Fuels in the Western U.S. are also building up due to a century of intentional wildfire suppression. “Prescribed fires are important to reduce fuels, while mitigating the effects of smoke,” she said. “For example, ozone, regulated by the Clean Air Act, is problematic in the summer season when conditions are optimal for ozone formation. Wildfire emissions can increase these concentrations. Altering the timing of smoke emissions through the use of prescribed burning so that emissions occur outside of the ozone season may have a positive effect and reduce health impacts.”

Ignition Sources on the Rise

Yet another factor driving changes in Western U.S. wildfires is a greater number of ignition sources, both natural and human-caused.

Map of California showing where 7,393 lightning strikes were detected for the 24-hour period ending at 6:00 a.m. on Tuesday, August 18, 2020.
For the 24-hour period ending at 6:00 a.m. on Tuesday, August 18, 2020, 7,393 lightning strikes were detected throughout the State of California. A massive, multiple-day thunderstorm event in mid-August sparked more than 650 wildfires across Northern California, including the August Complex fire, the single-largest wildfire in modern California history. Credit: U.S. Forest Service/Tahoe National Forest

Wildfires caused by lightning tend to occur in remote areas that are harder for firefighters to reach. These lightning-triggered wildfires are occurring more frequently. According to the U.S Forest Service, between 1992 and 2015, 44 percent of Western U.S. wildfires were triggered by lightning. Those fires were responsible for 71 percent of all land burned. Some studies predict climate change will increase the frequency of lightning in the future, but further research is needed.

A home stands in ruins following the CZU Lightning Complex Fire in California in August 2020.
A home stands in ruins following the CZU Lightning Complex Fire in California in August 2020. Credit: Cal OES, CC BY-NC 2.0

Human-caused fires are also on the rise, due to increased human development of land at what’s known as the wildland-urban interface – the edge of wildland areas. This significantly increases opportunities for both accidental and intentionally set wildfires. It also tends to make these fires more destructive to lives and property.

How Wildfires Are Impacting Climate

While the impact of climate change on wildfires is well-established, wildfires are also affecting climate, with associated impacts on ecosystems, air and water quality, and human health. These climate impacts may be significant.

Wildfires release carbon emissions that affect climate and drive climate change-related events that contribute to even more wildfires. The specific type of emissions they produce is determined by what they burn and how complete the combustion process is. The largest amounts of carbon emitted are in the form of carbon dioxide - a powerful greenhouse gas - and carbon monoxide. The quantity of each gas depends on whether a fire is flaming or smoldering. Dry fuels combust more easily and are more likely to be flaming.

Chart showing carbon emissions from California fires from 1997 to 2020, with record emissions happening in 2020
Carbon emissions from wildfires in California set new records in 2020, according to the Global Fire Emissions Database, which tracks emissions data from 1997 to the present. Credit: Global Fire Emissions Database

To put the carbon dioxide emissions from wildfires into perspective, September 2020 data from the Global Fire Emissions Database show that California wildfires in 2020 generated more than 91 million metric tons of carbon dioxide. That’s roughly 30 million metric tons more carbon dioxide emissions than the state emits annually from power production.

True (natural) color image of western U.S. wildfires on September 10, 2020 False (infrared) color image of western U.S. wildfires on September 10, 2020

Western U.S. Wildfires on September 10, 2020

In this side-by-side image, the left side image shows areas (marked in red) where wildfires were burning in the Western United States on September 10, 2020. Copious amounts of smoke spill off the coast and into the Pacific Ocean.

The right side, however, shows the real story of the danger that smoke poses. Using the OMPS (Ozone Mapping Profiler Suite) instrument, aerosols are detected and measured in terms of thickness and height of the atmospheric aerosol layer. For most atmospheric events involving aerosols, the AI ranges from 0.0 (colorless through light yellow, yellow, orange, and red) to 5.0 (deep red), with 5.0 indicating heavy concentrations of aerosols that could reduce visibilities or impact health. High aerosol concentrations not only can affect climate and reduce visibility, they also can impact breathing, reproduction, the cardiovascular system, and the central nervous system, according to the US EPA.

Since aerosols are able to remain suspended in the atmosphere and be carried in prevailing high-altitude wind streams, they can travel great distances away from their source and their effects can linger. The smoke released by any type of fire (forest, brush, crop, structure, tires, waste or wood burning) is a mixture of particles and chemicals produced by incomplete burning of carbon-containing materials. All smoke contains carbon monoxide, carbon dioxide and particulate matter (PM or soot).

Smoke can contain many different chemicals, including aldehydes, acid gases, sulfur dioxide, nitrogen oxides, polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, styrene, metals and dioxins. The type and amount of particles and chemicals in smoke varies depending on what is burning, how much oxygen is available, and the burn temperature. Credit: NASA Worldview

Wildfires also emit aerosols (tiny, floating solid and/or liquid particles of organic and inorganic matter). These aerosols can come in the form of black carbon, brown carbon, or both. When a fire is really hot, it produces more black carbon, commonly known as soot, char, or ash. When fires are less hot and smoldering, they produce more brown carbon, which reflects light, making it appear brown or yellow. Both types of carbon warm Earth’s climate, but black carbon has a stronger warming effect. Scientists currently know more about black carbon and its effects on climate than they do about brown carbon.

Scientists are also working to better understand the amount of ammonia wildfires release. When mixed with sunlight, ammonia produces two secondary aerosols - ammonium sulfate and ammonium nitrate – both of which have a cooling effect on climate. Ammonia also contributes to the formation of brown carbon.

Recently, scientists studying the devastating Australia wildfires of late 2019-early 2020 discovered that an outbreak of a rare type of fire-generated thundercloud had punched into Earth’s stratosphere, the second lowest layer of Earth’s atmosphere. The large quantity of smoke that made it into the stratosphere then circled the globe, reducing the amount of sunlight that reached the ground for several months. The smoke slightly cooled Earth’s surface by an as-yet undetermined amount (likely a small fraction of a degree, similar to the cooling effect of a moderate volcanic eruption). The event illustrates how large future wildfires may, at times, have a slight cooling effect on climate.

Photo of a pyrocumulonimbus cloud over the Pacific Northwest
Photo of a pyrocumulonimbus cloud over the Pacific Northwest taken from the cockpit of the NASA DC-8 aircraft on August 8, 2019, during the FIREX-AQ field campaign. Credit: Dr. David Peterson of the Naval Research Laboratory/ NOAA

Studying the trace gas and aerosol emissions from wildfires and prescribed burns was the objective of a joint 2019 NASA-NOAA field campaign called Fire Influence on Regional to Global Environments Experiment – Air Quality (FIREX-AQ). FIREX-AQ combined aircraft measurements, ground sampling and satellite data to correlate wildfire emissions to fuel and fire conditions on the ground; study wildfire plumes, including how they’re transported in the atmosphere and how they impact air quality downwind; and assess how effective satellites are in estimating fire emissions.

A woman on a balcony wears a face mask to protect herself against very dangerous levels of air pollution created by nearby wildfires.
A woman on a balcony wears a face mask to protect herself against very dangerous levels of air pollution created by nearby wildfires. Credit: Cal OES

The air quality impacts of the 2020 U.S. Western wildfires were truly extraordinary, at times making day as dark as night and tinging skies in major urban areas a surreal red. Some locations recorded air quality readings higher than 500 on the Air Quality Index scale (anything above 300 is considered hazardous to health). But smoke doesn’t know state or national boundaries - it drifted east thousands of miles across many parts of the United States, north into Canada and even as far as Europe. Researchers at Stanford University in Stanford, California, estimated California wildfire smoke likely led to at least 1,200 and as many as 3,000 excess California deaths between Aug. 1 and Sept. 10, 2020 alone.

A series of images above shows the abundance and distribution of black carbon, a type of aerosol found in wildfire smoke, as it rode jet stream winds across the United States
In September 2020, historic wildfires on the U.S. West Coast lofted plumes of smoke high into the atmosphere. Pushed by prevailing winds that sweep air from west to east, satellites tracked the smoke as it spread widely across much of the continental United States. A second hazard - tropical cyclones - also helped steer the high-flying smoke plumes as they streamed over the Midwest and Northeast between September 14-16, 2020.

The series of images above shows the abundance and distribution of black carbon, a type of aerosol found in wildfire smoke, as it rode jet stream winds across the United States. The black carbon data comes from the GEOS forward processing (GEOS-FP) model, which assimilates information from satellite, aircraft, and ground-based observing systems. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the NOAA-NASA Suomi NPP satellite acquired the images of the storms.

While satellite maps like this show smoke spanning the entire United States, that does not mean the smoke had equally strong effects on air quality at ground level everywhere. While people living in communities near the fires in California and Oregon faced very unhealthy and hazardous air quality between September 14-16, surface air quality in the eastern U.S. remained mostly good. That is because the smoke was traveling high in the atmosphere.

Credit: NASA Earth Observatory/Joshua Stevens, using GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC and VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi National Polar-orbiting Partnership

Another climate impact of U.S. Western wildfires is their role in converting ecosystems from one type to another. Wildfires are necessary for healthy forest ecosystems. They help clear the forest floor of dead organic material, allow sunlight to reach it, add nutrients to the soil, provide habitat for animals and birds by clearing heavy brush so new plants can grow, and kill disease and insect infestations, among their many benefits. But when their frequency or severity is disturbed, it can throw things dangerously out of whack. In time, this may lead to the loss of some forests, as climate change increases the frequency of fires and makes it harder for ecosystems to reestablish.

Chaparral covers the Santa Ynez Mountains near Santa Barbara, California
Chaparral covers the Santa Ynez Mountains near Santa Barbara, California. The leaves of some plants in chaparral communities actually require wildfires to reproduce. They are coated in oils that, when burned, create an intense fire that triggers the plant’s seeds to germinate. Once the new plants sprout, they have an advantage in the burned landscape due to a lack of competition. Credit: Antandrus at English Wikipedia., CC BY-SA 3.0, via Wikimedia Commons

“When you have major disturbance events like droughts and fires back-to-back in quick succession, you can change ecosystems,” Stavros said. “We’re starting to see this in some regions as wildfire frequency increases. Southern California’s mountains are covered with chaparral shrubs whose seedlings are only triggered to open by the extreme heat of a wildfire, and they’ve adapted to burning every seven to 15 years. If you increase the wildfire frequency, you begin depleting the seed bank and the chaparral may not regrow, because the only seedlings available for growth are often invasive species. In places like Arizona, Colorado, Washington, Oregon, and Idaho, we’re starting to see forests turn into prairies and grasslands. It’s not yet widespread, but it’s happening.”

Of course, the climate impacts of wildfires aren’t limited to the contiguous Western United States. In Alaska, increased wildfire activity is causing fires to burn through dense peatlands, releasing significant quantities of methane and carbon dioxide that exacerbate global warming. Other areas of global concern include Australia; Southeast Asia; the Amazon; Siberia, Canada and other parts of the Arctic; and even the Mediterranean region. The climate impacts of fires in each of these regions varies.

“The worst fires for climate are actually coming from Southeast Asia, the Amazon, and the Arctic, because you have carbon that’s been sitting there for a long time and then put back into the atmosphere when it burns,” Stavros said.

Adapting to a Fierier Future

Wildlife rescuers from the California Department of Fish and Wildlife examine a mountain lion with burn injuries from the September 2020 Bobcat Fire
Jamie Peyton of UC Davis and colleagues from the California Department of Fish and Wildlife examine a mountain lion with burn injuries from the September 2020 Bobcat Fire. Credit: CDFW

One thing is clear: fires are likely to become an increasingly consequential fact of life as the U.S. West continues to get warmer and drier. Society will need to adapt.

“The impact of fire is much more than just area burned,” Stavros said. “It’s lives lost, infrastructure damaged, degraded air quality. We can use our scientific understanding to inform systematic approaches to managing how we live in a world with fire: how and where we build, how and where we perform maintenance on power lines, etc.

“Everybody cares when they can see and smell the smoke, but when it’s gone, they stop,” she added. “But the problem isn’t going to go away.”

September 8, 2020, 15:29 PDT

Making Sense of ‘Climate Sensitivity'

New Study Narrows the Range of Uncertainty in Future Climate Projections

By Alan Buis,
NASA's Jet Propulsion Laboratory

NASA GISS Surface Temperature Analysis (GISTEMP v4) trend map of observed global surface temperature change for the period from 1979 to 2019. Future global warming depends on Earth's climate sensitivity and our emissions. Credit: NASA's Goddard Institute for Space Studies

NASA GISS Surface Temperature Analysis (GISTEMP v4) trend map of observed global surface temperature change for the period from 1979 to 2019. Future global warming depends on Earth's climate sensitivity and our emissions. Credit: NASA's Goddard Institute for Space Studies

Recently, an international research team published a comprehensive review in the journal Reviews of Geophysics on our state of understanding of Earth's "climate sensitivity," a key measure of how much our climate will change as greenhouse gas emissions increase. Essentially, by narrowing the range of estimates, the researchers found that climate sensitivity isn’t so low that it should be ignored, but it’s also not so high that there is no hope for the planet’s recovery.

We asked the two NASA authors on the study — Kate Marvel, jointly of Columbia University in New York and NASA’s Goddard Institute of Space Studies (GISS) in New York; and GISS Director Gavin Schmidt — to discuss their roles in the study and its significance for understanding the impacts of our warming world on climate.

Q. What exactly is climate sensitivity and why is it important to know its true value?

Schmidt: “We know from studies of the past that Earth’s climate can change dramatically. The evidence shows that the amount of greenhouse gases in the atmosphere can vary over time and make a big difference to the climate. Scientists try to quantify that by estimating how much the surface air temperature, averaged over the whole globe, would change if we doubled the amount of one typical but specific greenhouse gas – carbon dioxide. That number, called climate sensitivity, has quite a wide uncertainty range, and that has big implications for how serious human-made climate change will be.”

Q. Your team was able to narrow the range of estimates of Earth's climate sensitivity by more than 43 percent, from the previously accepted range of 1.5 to 4.5 Kelvin first established in 1979 (roughly 3 to 9 degrees Fahrenheit), to a narrower range of 2.6 to 3.9 Kelvin (roughly 4.5 to 7 degrees Fahrenheit). Why is it important for scientists to narrow this range of uncertainty? What does it mean in practical terms to be able to reduce uncertainties in measuring climate sensitivity?

Schmidt: “Scientists would like to reduce that uncertainty so that we can have more confidence in how we need to mitigate and adapt to future changes. For instance, how much sea level might rise, or how heat waves will get worse, or rainfall patterns change, are tied to the climate sensitivity combined with our actions in changing the atmosphere. A higher climate sensitivity would mean we would have to do more to avoid big changes, while a lower value would mean we’d have more time to adapt. It’s useful to note that we expect to reach double carbon dioxide levels later this century, and that while a few degrees might not seem like much, it's a big deal for the planet. The difference between forests beyond the Arctic Circle or glaciers extending down to New York City is only a range of about 8 K (about 14 degrees Fahrenheit) in the global average, while it changes sea level by 150 meters (more than 400 feet)!”

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Q. How can better estimates of climate sensitivity impact policy decisions?

Marvel: “The most important thing about climate sensitivity is that it's not zero. Increasing atmospheric carbon dioxide definitely makes it warmer and increases the risk of extreme weather like drought, downpours, and heat waves. But better estimates of climate sensitivity are important for motivating action. Our results show that it would be foolish to rely on nature to save us from climate change — we don't think it's likely that sensitivity is low. But conversely, it's unlikely that climate sensitivity is so high as to make action pointless.”

Schmidt: “I’m not sure that our policy decisions are that finely tuned to the science of climate sensitivity other than knowing that climate really is sensitive to increasing greenhouse gases. Many climate policies are robust to those uncertainties, but many adaptation decisions will depend on knowing how bad things will get.”

Q. Why has it been so difficult over the past 40 years to narrow this range? What made this new estimate possible?

Schmidt: “There are three main reasons why this has been difficult. First, knowledge of past climate change has been difficult to quantify in globally coherent ways. Of course, we have known about the ice ages for a century or more, but getting accurate estimates of the global changes in temperature, greenhouse gases, and ice sheets has taken time and has needed many scientists working on many different aspects of the problem to come together. Second, the climate change signal has taken time to come out of the ‘noise’ of normal variability. In the 1980s and 1990s, people were still arguing about whether the warming over the 20th century was significant, but with another 20 years of record-breaking temperatures, that has been very clearly shown. Third, our understanding of the processes in the climate that affect sensitivity — clouds, water vapor, aerosols, etc. — has improved immensely with the development of satellite remote sensing, and every decade we are producing better and more useful information. But as these lines of evidence have matured, the need to come up with new methods to tie them all together coherently has become acute — and that was the impetus for this roughly 4-year effort.”

Marvel: “Yes, and in modeling, clouds are some of the biggest wildcards. See go.ted.com/katemarvel.”

Q. What types of evidence did the team consider in reaching its conclusions? Where do the lines of evidence agree and disagree most substantially?

Schmidt: “There are three main sources of information: changes since the late 19th century that have been measured in real time, our understanding of physical processes (particularly clouds), and new and more complete information from periods in the paleoclimate record (the geological past) where the planet was significantly cooler or warmer than today. All of the lines of evidence are mostly commensurate, but specific issues mean that the recent record isn’t good at constraining the high-end values because of the imprecise role of aerosols, and paleoclimate change is less able to constrain the low end because of the uncertain nature of that data. Together, however, we can mostly rule those tails out.”

Q. What were a few of the most significant findings for each of the three lines of evidence studied (feedback processes, the historical warming record, and paleoclimate records)?

Marvel: “For a long time, many people thought that sensitivity estimates derived from paleoclimate — the far past — were incompatible with estimates derived from more recent observations. But there's a difference between a past climate state in which the planet has reached an equilibrium — a ‘new normal’ — and our current climate, where things are very much in flux and continuing to change. There is some uncertainty in just how different the future will look from what we're experiencing now — it's possible we're moving into a new world for which we don't have a recent analogue. And when we take that uncertainty into account in a rigorous way, we find that the far past and the near future may not be telling us such different things after all.”

Schmidt: “What was interesting was that by starting off with a view of climate sensitivity that was a little more sophisticated than people had used previously, we found that there was more coherence among the different lines of evidence than others had found, and since the information we are using really is very independent, that allowed us to narrow the uncertainty.”

Q. Your team used a "Bayesian approach" to calculate your estimated range of climate sensitivity. In layman's terms, what is that?

Schmidt: “A Bayesian approach is really just a mathematical representation of how we do science in general. We have an initial hypothesis, we get some evidence that may or may not support it, and then we update our understanding based on that evidence. And then we do it again (and again, and again, etc.). Over time, and as more evidence accumulates, we hopefully hone in on the most correct answer. Using Bayesian methods allowed us to pull together disparate threads of evidence in a coherent way — allowing for different degrees of confidence in each of the lines of evidence. What is great is that in the future, as more evidence is discovered, we can continue the process and update our understanding again.”

Q. What role did global climate models play in the team's findings?

Marvel: “Complex climate models are useful tools (see here for a good overview). But in this paper, we relied largely on observations: satellite and ground-based measurements of recent trends, paleoclimate datasets, and basic physical principles.”

Schmidt: “Climate models help frame the questions we are asking and can be examined to see how climate patterns in space and time connect to things we can directly observe. But we know that climate models have a lot of uncertainty related (for instance) to cloud processes, and so we didn’t use them directly to estimate sensitivity. You could, however, use our results to assess whether a climate model has a sensitivity that is within our independently constrained range.”

Q. Your new estimated range of Earth's climate sensitivity finds the value is around the mid-point of the previous estimate range rather than on the lower or higher end. What does that mean in practical terms for projections of Earth's global temperatures and Earth's climate in this century?

Schmidt: “It means that climate sensitivity is not so low that we can ignore it, nor is it so high that we should despair. Ultimately, it tells us that while human-made climate change is (and will continue to be) a problem, our actions as a society can change that trajectory.”

Q. How likely is it that Earth's climate sensitivity could be higher than 3.9 Kelvin? Lower than 2.6 Kelvin?

Schmidt: “There are subjective elements to the analysis we performed, and other people could decide to weight things a little differently. We explored some of these alternative choices and that broadens the uncertainty a little, but basically, we estimate that there is about a one-in-six chance that it was less than the low end, and one-in-six that it was higher than the high end. That’s not impossible, but, if true, then a lot of our assessments would have to be quite a ways off.”

Q. The concentration of carbon dioxide in Earth's atmosphere is currently around 414 ppm (parts per million). What are the projections for future carbon dioxide increases under the range of current emissions scenarios and how does having a better estimate of climate sensitivity improve our understanding of how our climate may change in the future?

Schmidt: “The future trajectory of carbon dioxide will depend on what we do as a society — if we decide to burn all the fossil fuels we can find, we could reach 900 ppm by the end of the century, but if we aggressively reduce emissions, we could stay below 500 ppm, maybe lower. The climate sensitivity tells us what we can expect in terms of temperature — between another 1 or 2 degrees Celsius (1.8 or 3.6 degrees Fahrenheit) for the low scenario, which would be very serious, to between 4 and 7 degrees Celsius (7.2 and 12.6 degrees Fahrenheit) for the high end scenario, which would be a disaster.”

Q. What about your study did you find most surprising?

Marvel: “How difficult it was to get everyone with all their different expertise working together on a big, joint effort. In the end, I think everyone realized how important it was and how this will be a strong basis for everyone’s future research.”

Schmidt: “How consistent the results were across all three different approaches.”

Q. What was your role in the study?

Marvel: “I was one of the lead scientists on the section looking at historical constraints on sensitivity, making sure that we took into account the differences in how things changed over the 20th century and how things will change going forward, and working to make sure that the uncertainties in historical climate records were properly included.”

Schmidt: “I worked mainly on the paleoclimate section, making sure that we used the most appropriate data from key periods in the planet’s history (like the last ice age or the last time carbon dioxide was as high as it is now — some 3 million years ago).”

July 14, 2020, 08:47 PDT

Sea Level 101, Part Two: All Sea Level is ‘Local'

By Alan Buis,
NASA's Jet Propulsion Laboratory

Global sea level rise impacts all coastlines differently due to numerous factors. The height of the ocean relative to the land along a coastline is referred to as relative sea level. Credit: joiseyshowaa/Flickr CC BY-SA 2.0

Global sea level rise impacts all coastlines differently due to numerous factors. The height of the ocean relative to the land along a coastline is referred to as relative sea level. Credit: joiseyshowaa/Flickr CC BY-SA 2.0

As discussed in our last Sea Level 101 blog post, we know sea level on the open ocean isn’t really flat. A number of factors combine to determine the topography of the ocean surface.

Global sea level rise is complex as well. To begin with, it has multiple causes, including the thermal expansion of the ocean as it warms, runoff of meltwater from land-based ice sheets and mountain glaciers, and changes in water that’s stored on land. These factors combine to raise the height of our global ocean about 3.3 millimeters (0.13 inches) every year. That rate is accelerating by another 1 millimeter per year (0.04 inches per year) every decade or so.

Factors that contribute to sea level change.
Factors that contribute to sea level change. Credit: Intergovernmental Panel on Climate Change 2001

Another factor that makes sea level rise complex is that it’s not uniform around the globe. If you look at a global map of sea level rise, you’ll find it’s happening rapidly in some places and more slowly in others. This means that although sea level rise affects coastal areas all over our ocean planet, some regions feel its effects sooner and more severely than others. This is reflected in future projections of sea level rise, with many cities in Asia expected to be among the hardest hit localities. Here in the United States, cities expected to see the worst impacts include New York, Miami and New Orleans, to name but a few.

Total sea level change between 1992 and 2014, based on data collected from the U.S./European Topex/Poseidon, Jason-1, and Jason-2 satellites.
Total sea level change between 1992 and 2014, based on data collected from the U.S./European Topex/Poseidon, Jason-1, and Jason-2 satellites. Credit: NASA’s Scientific Visualization Studio

Indeed, at any given place and time around our planet, sea level rise varies. But why is that? It turns out that when it comes to sea level rise, it’s all local. And it’s all relative.

Relative Sea Level

“Relative sea level” refers to the height of the ocean relative to land along a coastline. Common causes of relative sea level change include:

  • Changes due to heating of the ocean, and changes in ocean circulation
  • Changes in the volume of water in the ocean due to the melting of land ice in glaciers, ice caps, and ice sheets, as well as changes in the global water cycle
  • Vertical land motion (up or down movements of the land itself at a coastline, such as sinking caused by the compaction of sediments, or the rise and fall of land masses driven by the movement of continental or oceanic tectonic plates)
  • Normal, short-term, frequent variations in sea level that have always existed, such as those associated with tides, storm surges, and ocean waves (swell and wind waves). These variations can be on the order of meters or more (discussed in more detail in our previous blog post).

Let’s look at these factors more closely.

When you heat up water, it expands and takes up more space. How much it expands depends on how deep the warming occurs as well as the temperature of the water to begin with. For example, in Earth’s tropics, a 1-degree Celsius (1.8 degrees Fahrenheit) warming in the temperature of the top 100 meters (328 feet) of the ocean raises sea level there by about 3 centimeters (1.2 inches). This thermal expansion of the ocean is responsible for between one-third and one-half of the overall global sea level rise observed over the last two decades. Because Earth’s ocean isn’t warming at the same rate everywhere, it results in regional differences in relative sea level rise, with areas that are warming faster seeing faster sea level rise.

Diagram explaining the concept of thermal expansion of the ocean.
Diagram explaining the concept of thermal expansion of the ocean. Credit: Roseanne Smith / CC BY 4.0
Ocean heat content in 2018 compared to the 1955-2006 average.
Ocean heat content in 2018 compared to the 1955-2006 average. Orange and blue areas show where the upper 700 meters (2,300 feet) of the global ocean gained or lost up to 3 gigajoules (109 joules) of heat energy per square meter compared to the long-term average. Warming of ocean water is raising global sea level because water expands when it warms. Credit: NOAA

Changes in ocean circulation also contribute to regional sea level differences. For example, in the United States, El Niño, a cyclical, naturally-occurring ocean circulation pattern of warming (in the central and eastern tropical Pacific Ocean) and cooling (in the western tropical Pacific Ocean) can temporarily raise relative sea level along the West Coast by more than a foot for up to a couple of years. Similarly, along the U.S. East Coast, the speedup or slowdown of the major ocean current known as the Gulf Stream can temporarily add or subtract as much as 5 centimeters (2 inches) of sea level height to local coastlines.

The El Niño of 2015-2016 was the biggest, so far, of the 21st century.
The El Niño of 2015-2016 was the biggest, so far, of the 21st century. This image shows a side-by-side comparison of Pacific Ocean sea surface height anomalies during the 2015-16 event with the famous 1997-1998 El Niño. The images were made from data collected by the U.S./European Topex/Poseidon (1997-1998) and OSTM/Jason-2 (2015-2016) satellites. Credit: NASA-JPL/Caltech

Next, there’s melting land ice in the Greenland and Antarctic ice sheets and Earth’s glaciers and ice caps. The largest contribution is from Greenland, which loses hundreds of billions of tons of ice a year and is a major contributor to sea level rise across the globe. As Greenland loses ice, the land beneath its ice sheet rises as the weight of the ice sheet is removed. As a result, Greenland itself doesn’t see any local sea level rise.

But all of its melted ice — currently averaging 281 gigatons a year, as measured by the U.S./German Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) satellite missions — has to go somewhere. Gravity causes it to flow into the ocean, causing sea level to rise thousands of miles away. Data from GRACE-FO tell us that melting land ice in glaciers, ice caps, and ice sheets contributed about two-thirds of global sea level rise during the last decade.

The mass of the Greenland ice sheet has rapidly declined in the last several years due to surface melting and iceberg calving. Research based on observations from the NASA/German Aerospace Center’s twin Gravity Recovery and Climate Experiment (GRACE) satellites indicates that between 2002 and 2016, Greenland shed approximately 280 gigatons of ice per year, causing global sea level to rise by 0.8 millimeters (0.03 inches) per year.

These images, created from GRACE data, show changes in Greenland ice mass since 2002. Orange and red shades indicate areas that lost ice mass, while light blue shades indicate areas that gained ice mass. White indicates areas where there was very little or no change in ice mass since 2002. In general, higher-elevation areas near the center of Greenland experienced little to no change, while lower-elevation and coastal areas experienced up to 4 meters (13.1 feet) of ice mass loss (expressed in equivalent-water-height; dark red) over a 14-year period. The largest mass decreases of up to 30 centimeters (11.8 inches) (equivalent-water-height) per year occurred along the West Greenland coast. The average flow lines (grey; created from satellite radar interferometry) of Greenland’s ice converge into the locations of prominent outlet glaciers, and coincide with areas of high mass loss. Credit: NASA

As land ice in Greenland, Antarctica and elsewhere melts, it changes Earth’s gravity field and slightly shifts the direction of Earth’s rotation. This causes uneven changes in sea level across the globe. Each melting ice mass around the world creates its own unique pattern of sea level change in the global ocean. For example, when ice melts in Antarctica, the amount of sea level rise it generates in California and Florida is up to 52 percent greater in those locations than if the global ocean just filled up uniformly, like water in a bathtub. Scientists use gravity data from the GRACE-FO mission to calculate patterns of sea level change associated with the loss of ice from glaciers, ice caps and ice sheets, as well as from changes in land water storage.

An animation showing “sea level fingerprints,” or patterns of rising and falling sea levels across the globe in response to changes in Earth’s gravitational and rotational fields. The movement of water across our planet can cause localized bumps and dips in gravity, sometimes with counterintuitive effects. Melting glaciers, for example, actually cause nearby sea level to drop; as they lose mass, their gravitational pull slackens, and sea water migrates away.

In this animation, computed from data gathered by the twin GRACE satellites since 2002, sea level is dropping around rapidly melting Greenland (orange, yellow). But near coastlines at a sufficient distance, the added water causes sea levels to rise (blue). The computational method is described in Adhikari et al. (2016, Geoscientific Model Development). These solutions are presented in Adhikari and Ivins (2016, Science Advances). Credit: NASA-JPL/Caltech

Then there’s vertical land motion along coastlines. When land sinks (a process known as subsidence), it causes a relative increase in sea levels. When land rises (known as uplift), it results in a relative decrease in sea levels.

A number of factors, both natural and human-produced, cause land to rise or sink, including:

  • Adjustments related to the rebound of land during and following the retreat of past ice sheets in North America and Eurasia at the end of the last Ice Age (known as isostatic, or post-glacial, rebound). The retreat of the ice sheets lightened the load of mass on the underlying mantle deep below Earth’s surface, causing Earth’s surface there to slowly rise. Land areas that were once near the edge of these ancient ice sheets, such as along the U.S. eastern seaboard, are today falling, exacerbating sea level rise there.
    A model of present-day vertical land motion due to post-glacial rebound and the reloading of the ocean basins with seawater.
    A model of present-day vertical land motion due to post-glacial rebound and the reloading of the ocean basins with seawater. Blue and purple areas indicate rising due to the removal of the ice sheets. Yellow and red areas indicate falling as mantle material moved away from these areas in order to supply the rising areas, and because of the collapse of the forebulges around the ice sheets. Credit: NASA-JPL/Caltech
  • Plate tectonics. Earth is divided into multiple slowly moving tectonic plates that interact with each other along plate boundaries. At some plate boundaries, the motion of one plate under, over, or past another results in vertical uplift or subsidence of the land surface above.

  • Natural or human-produced compaction of sediments, such as those caused by pumping groundwater, or oil and gas. Subsidence related to groundwater withdrawal can be especially pronounced in areas with large populations and extensive agriculture. Sediments can also be compacted by construction activities by humans or by the natural settling of new soils. In the United States, subsidence is a major factor in relative sea level rise along parts of the Gulf and East Coasts.

The ruins of a Civil War-era structure, Fort Beauregard, lie partially submerged east of New Orleans.
The ruins of a Civil War-era structure, Fort Beauregard, lie partially submerged east of New Orleans. Researchers say many large coastal cities around the world sink faster than sea levels rise at their location. Credit: Frank McMains

Oceanographer and climate scientist Josh Willis of NASA’s Jet Propulsion Laboratory in Southern California says that when it comes to relative sea level rise at any particular coastal location, subsidence is the most immediate consideration.

“People in coastal areas need to know what the land is doing right now where they live,” he said. “Is it sinking? If so, how fast? When you combine a sinking coastline with sea level rise caused by other contributing factors, you’re in trouble. Remember, scientists are projecting feet of global-mean sea level rise in this century. But in some places, land can sink by one foot in a decade. We have to understand all of these pieces before we can project future sea level rise at a beach near you.”

June 23, 2020, 09:33 PDT

Sea Change: Why Long Records of Coastal Climate Matter

A Monitoring Station off the Coast of Spain Is Giving Scientists a Front-Row Seat to Understanding the Region’s Long-Term Climate Change

By Alan Buis,
NASA's Jet Propulsion Laboratory

L'Estartit, a small Spanish coastal town in the Catalan Costa Brava region of the northwestern Mediterranean Sea. A half-century of continuous data from a meteorological and oceanographic coastal station here are giving scientists important insights into the region's long-term climate trends. Credit: Cnestartit / CC BY-SA

L'Estartit, a small Spanish coastal town in the Catalan Costa Brava region of the northwestern Mediterranean Sea. A half-century of continuous data from a meteorological and oceanographic coastal station here are giving scientists important insights into the region's long-term climate trends. Credit: Cnestartit / CC BY-SA

Climate scientists will tell you a key challenge in studying climate change is the relative dearth of long-term monitoring sites around the world. The oldest continuously operating station — the Mauna Loa Observatory on Hawaii’s Big Island, which monitors carbon dioxide and other key constituents of our atmosphere that drive climate change — has only been in operation since the late 1950s.

This obstacle is even more profound in the world’s coastal areas. In the global open ocean, the international Argo program’s approximately 4,000 drifting floats have observed currents, temperature, salinity and other ocean conditions since the early 2000s. But near coastlines, the situation is different. While coastal weather stations are plentiful, their focus is to produce weather forecasts for commercial and recreational ocean users, which aren’t necessarily useful for studying climate. The relative lack of long-term records of surface and deep ocean conditions near coastlines has limited our ability to make accurate oceanographic forecasts.

A meteorological and oceanographic coastal station in the small Spanish coastal town of L’Estartit is a notable exception. Located in the Catalan Costa Brava region of the northwest Mediterranean Sea, the L’Estartit station has collected inland data on air temperature, precipitation, atmospheric pressure and humidity since 1969, and has also made oceanographic observations at least weekly since 1973. This makes L’Estartit the longest available uninterrupted oceanographic data time series in the Mediterranean. A new NASA-funded study presents a detailed analysis of the site, revealing climate trends for its Mediterranean coastal environment spanning nearly a half century.

“The long-term data set from L’Estartit is a treasure trove that’s useful for assessing the regional impacts of climate change and how it’s evolved over time."
- JPL oceanographer Jorge Vazquez

The study, led by Jordi Salat of the Institut de Ciències del Mar (CSIC) in Barcelona, provides estimates of annual trends in sea and atmospheric temperature and sea level, along with seasonal trends. It also compares data from the site with previous and other estimates of climate trends in the region. Co-authors include Josep Pascual, also with CSIC; oceanographers Jorge Vazquez and Mike Chin of NASA’s Jet Propulsion Laboratory in Southern California; and Mar Flexas of Caltech, also in Southern California.

The Evolution of Modern Ocean Monitoring

The existence of the L’Estartit station reflects the results of decades of scientific research dating back to the 20th century. This body of work has established the vital role the ocean plays, in conjunction with our atmosphere, in shaping Earth’s global weather and climate. While sea level and sea state have been monitored regularly for some time, other measurements of oceanic conditions haven’t been as well-chronicled. In order to reconstruct the climate history of the ocean, scientists have typically relied on data from coastal tide gauges and stationary mooring stations, along with oceanographic cruises that weren’t generally part of any coordinated monitoring program.

By the 1980s, however, as Earth’s global climate warming trend became evident, scientists began to establish international programs to conduct long-term studies of the ocean. As a result, in recent years, scientists have increasingly acknowledged the value of having the oceanographic equivalent of weather forecasts. Maintaining regular, long-term records of air temperature, water temperatures at the surface and at various depths, winds, sea level, salinity, and other key oceanographic parameters gives scientists valuable information on long-term average values, how variable our climate is and on long-term changes and trends. Moreover, they help scientists better evaluate how humans are contributing to climate change.

Over the past 20 to 30 years, new technologies have given scientists the ability to monitor the ocean all the way from the sea surface to the ocean floor. These include satellites, drifters, gliders, moorings, buoys, Argo profilers and ship data. These data are used as inputs to computer models to estimate the state of the ocean, make ocean forecasts and estimate climate trends.

L’Estartit: Monitoring a Climate Hot Spot

Maintained by voluntary observer Josep Pascual in collaboration with CSIC and the authority of the marine protected area, the L’Estartit station is well positioned to monitor the Mediterranean, a region of our planet that’s significantly impacted by climate change. It lies at the southern end of a relatively narrow offshore continental shelf and along the coastal side of the Northern Current, the main along-slope ocean current in the northwestern Mediterranean.

L'Estartit station location 1
Ocean observations for the L'Estartit station are collected from a fixed point located about 4 kilometers offshore (the orange circle in the right center of the image).Credit: Adapted from Figure 1 of Salat et al. (2019)
L'Estartit location 2
The locations of the L'Estartit station's meteorological box (magenta circle), sea level gauge (red triangle) and wind station (blue diamond) are depicted on a map (b), and on a photo (c). Credit: Adapted from Figure 1 of Salat et al. (2019)

You can think of the Mediterranean as sort of a miniature ocean, since most of the processes that take place in the global ocean also take place here, albeit at different time scales in some instances. Its relatively small size also makes it more accessible to monitoring than many other regions of the global ocean. Because it’s located in Earth’s mid latitudes, it experiences significant seasonal variations, which affect the way it exchanges heat with the atmosphere.

The L’Estartit site collects a broad array of oceanographic data. In addition to the data mentioned previously, the site began continuous measurements of potential daily evaporation in 1976; and has measured sea state, along with wind speed and direction, since 1988. With the installation of a tide gauge in the harbor in 1990, continuous sea level data have been collected. Also added in the 1990s were conductivity-temperature-depth (CTD) profiles and water samples to analyze the temperature and salinity of the water column.

L’Estartit’s long-term data record makes it possible for scientists to calculate trends for a variety of atmospheric and oceanic climate attributes, including air temperature, sea surface and sub-surface temperature to a depth of 80 meters (262 feet), air pressure, relative humidity, relative cloudiness, wind, salinity, changes in ocean stratification, estimates of favorable conditions for evaporation, sea level and precipitation.

“The long-term data set from L’Estartit is a treasure trove that’s useful for assessing the regional impacts of climate change and how it’s evolved over time,” said Vazquez. “The data can be used as reference for other areas in the Mediterranean. The strong agreement between the site’s measurements of sea surface temperatures and satellite data of sea surface temperatures demonstrates how L’Estartit can serve as both a long-term ground truth site to validate satellite observations and as a regional monitoring site for climate change.”

Vazquez says data from the site have been used in numerous climate research studies and have also been used to document a variety of extreme events, from cold spells and heat waves to storms.

A Half-Century of Climate Trends

The researchers’ analysis of the nearly 50-year data set reveals numerous climate trends. For example, air temperature has increased by an average of 0.05 degrees Celsius (0.09 degrees Fahrenheit) per year during this time. Sea surface temperature has increased by an average of 0.03 degrees Celsius (0.05 degrees Fahrenheit) per year, while the temperature of the ocean at a depth of 80 meters (262 feet) has increased by an average of 0.02 degrees Celsius (0.04 degrees Fahrenheit) per year.

Monthly temperature anomalies - air, sea surface, sea 80 m
a) Time series of monthly air temperature anomalies (line), annual mean (squares) and linear trend. b) Time series of monthly sea surface temperature anomalies (line), annual mean (blue squares), winter (pink triangles), spring (small green squares), summer (red squares) and autumn (brown circles). Seasonal trend lines are colored according to the symbols. c) Time series of monthly sea temperature anomalies at a depth of 80 meters (line), annual mean (squares), autumn values (brown circles) and their linear trends. Credit: Figure 6 of Salat et al. (2019)
L'Estartit mean sea level anomaly (cm)
Time series of monthly sea level anomalies at the L'Estartit station, with trend lines for mean, maximum and minimum values. Credit: Figure 8 of Salat et al. (2019)

While sea level in the Mediterranean decreased from the 1960s to the 1990s due to changes in the North Atlantic Oscillation (a multi-decadal cyclical fluctuation of atmospheric pressure over the North Atlantic Ocean that strongly influences winter weather in Europe, Greenland, northeastern North America, North Africa and northern Asia), it’s been on the rise since the mid-1990s. The L’Estartit data show that sea level at that site is currently rising at a rate of 3.1 millimeters (0.12 inches) per year.

The researchers found that some of the long-term climate trends they observed were more pronounced during some seasons than in others. For example, trends in air temperature and sea surface temperature were significantly stronger during spring, while the trend for ocean temperature at 80 meters was greatest during autumn. Among their other findings, they noted a small increase in the number of days per year that experience summer-like sea conditions. They also found an almost two day per year drop in conditions favorable for marine evaporation, which may be related to an observed decrease in springtime coastal precipitation.

Vazquez says the good statistical comparison between sea surface temperature values and trends from the L’Estartit data set and data from available satellite products is encouraging. “The long-term consistency of the direct measurements with our satellite data gives scientists the opportunity to validate climate trends across multiple decades,” he said. “Data from L’Estartit should serve as a wake-up call to the global climate science community to immediately begin similar initiatives and ensure their continuity over time.”

The L’Estartit data are available to the public free of charge. The digitized data are accessible at http://meteolestartit.cat/. The remote sensing data used in the study may be retrieved through NASA’s Physical Oceanography Distributed Active Archive Center (PO.DAAC) at http://podaac.jpl.nasa.gov.

June 3, 2020, 07:20 PDT

Sea Level 101: What Determines the Level of the Sea?

By Alan Buis,
NASA's Jet Propulsion Laboratory

Photo of the Pacific Ocean. Credit: Michael Matti, Flickr/Creative Commons

Photo of the Pacific Ocean. Credit: Michael Matti, Flickr/Creative Commons

Lots of forces are at work on the world’s ocean, and NASA studies them all. When it comes to sea level, NASA does much more than just measure it; they also seek to understand it. But for non-scientists, fathoming the forces that determine sea levels around the world can sometimes be a bit daunting, so here’s a little guide to some of the basics.

Let’s dive in.

Fathoming the forces that determine global sea levels can be daunting. We present a guide to the basics of ocean surface topography. Credit: NASA/JPL-Caltech

Waves in the Bathtub

Most of the time, Earth’s ocean looks pretty darn flat to those of us here on the ground, like the water in a bathtub. If you’re on a boat at sea, the only topography you’re going to notice on the ocean is waves. Generated by the friction between wind and water, wind waves range from tiny ripples on a calm sea to storm-generated monsters that can tower more than 100 feet (30 meters) high. Some wind waves are generated locally. Others, called swells, which result from winds that blew somewhere else in the past, travel across the ocean surface.

Rough seas
Rough seas. Credit: CSIRO/CC BY 3.0

But even in the absence of waves, it turns out the ocean isn’t really flat at all. It has hills and valleys just like land surfaces do, though they’re relatively small — up to about 2 meters (6.5 feet) high.

Dynamic ocean topography map
The ocean’s “dynamic” topography tells oceanographers the speed and direction of ocean currents in the same way that maps of atmospheric pressure are used by meteorologists to calculate the speed and direction of winds. It reveals the height of the ocean relative to the geoid, a surface where gravity is always uniformly pointed downward. The dynamic ocean topography shown in this map was created from 10 days of data from the NASA/CNES Topex/Poseidon satellite mission, and varies by about 2 meters (6.6 feet) from its highest to lowest places. The color scale corresponds to the grades of the relief in centimeters. The vertical scale is greatly exaggerated to illustrate the three-dimensional perspective of the topography. Credit NASA/JPL-Caltech

These small variations in ocean surface topography are influenced by many factors, including the temperature of the water, how much salt it contains (its salinity), the pressure of the atmosphere above the ocean surface, and ocean currents.

Currents move ocean waters around our planet over long distances, primarily in a horizontal direction, reshaping the ocean’s surface and causing it to tilt. They’re generated by various forces, including winds, breaking waves, ocean temperature, salinity, and a phenomenon known as the Coriolis effect (which causes water and wind to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere). Currents flow around the ocean’s hills and valleys, much like wind blows around areas of high and low pressure in our atmosphere.

Ocean currents happen in the open ocean and generally don’t have a big impact on coastlines, with a few major exceptions, such as the Gulf Stream in the Atlantic Ocean along the U.S. East Coast and a similar Pacific Ocean current off the coast of Japan called the Kuroshio, which transports water northward up Japan’s east coast and then due east. As our planet warms, it affects wind patterns that drive most of these currents, changing them.

Visualization of the Gulf Stream stretching from the Gulf of Mexico to Western Europe
Visualization of the Gulf Stream stretching from the Gulf of Mexico to Western Europe. Credit: NASA's Scientific Visualization Studio

While all of these factors are important drivers of ocean surface topography, there’s an even larger force working to shape the ocean: changes in Earth’s geoid. The geoid is the shape that Earth’s ocean surface would take if the only influences acting upon it were gravity and Earth’s rotation. Changes in the solid Earth affect Earth’s gravitational field, causing the height of Earth’s geoid to vary by up to 100 meters (328 feet) around the globe. For example, in places where Earth’s crust is thick and dense, the gravitational pull causes extra water to pile up. In addition, the shape of the geoid is partly determined by geologic features on the floor of the ocean, including seamounts (underwater mountains) and valleys, which pull the water due to the force of gravity.

Gravity anomaly map
If our ocean had no tides or currents, the sea surface would assume the shape of the geoid. These "gravity anomaly" maps, based on data from the U.S./German Gravity Recovery and Climate Experiment (GRACE) mission, show where Earth's gravity field differs from a simplified Earth model that is perfectly smooth and featureless. Areas colored yellow, orange or red are areas where the actual gravity field is large, such as the Himalayan Mountains in Central Asia (top left of the left-hand globe). The progressively darker shades of blue indicate places where the gravity field is smaller, such as the area around Hudson Bay in Canada (top center of right-hand globe). Credit: NASA/JPL-Caltech

Topographic features on the open ocean can only be seen from space, by specialized instruments called altimeters that precisely measure the height of the ocean surface.

Since 1992, NASA has partnered with other U.S. and European institutions on multiple satellite missions to map ocean surface topography. They include the joint NASA/Centre National d'Etudes Spatiales (CNES) Topex/Poseidon mission, which operated from 1992 to 2005; the NASA/CNES Jason-1, which operated from 2001 to 2013; the joint NASA/CNES/National Oceanic and Atmospheric Administration (NOAA)/European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Jason-2/Ocean Surface Topography Mission (OSTM), which operated from 2008 to 2019; and the current Jason-3, an international partnership led by NOAA with participation by NASA, CNES and EUMETSAT, launched in 2016. This November, Sentinel-6 Michael Freilich will launch to continue this long-term data set. The new mission is jointly developed by the European Space Agency (ESA), EUMETSAT, NASA and NOAA with funding support from the European Commission and support from CNES.

Sentinel-6 Michael Freilich satellite
The Sentinel-6A Michael Freilich satellite, scheduled for launch in November 2020, will extend a nearly 30-year data record of mapping ocean surface topography and monitoring changes in global sea level. Credit: ESA/NASA

Measuring ocean surface topography allows us to understand ocean circulation (how our ocean stores energy from the Sun and moves it around our planet), accurately track changes in global sea level, and understand how the ocean joins forces with Earth’s atmosphere to create our weather and climate, including phenomena such as El Niño and La Niña and weather patterns such as hurricanes and other storms.

A Flattening Map

23-year trend of rising seas across the globe from 1993 to 2016
For nearly 30 years, satellite altimeters have measured the sea surface height of our ever-changing ocean. This image shows the 23-year trend of rising seas across the globe from 1993 to 2016. The grids and figures were produced at NASA’s Jet Propulsion Laboratory under the NASA MEaSUREs program. Credit: NASA/JPL-Caltech

A look at a current map of trends in the nearly 30-year satellite record of global ocean surface topography reveals clear regional differences across the globe, with variations of up to 20 centimeters (8 inches) of sea level rise and fall from one place to another. But, says Josh Willis of NASA’s Jet Propulsion Laboratory in Pasadena, California, NASA’s project scientist for the Jason-2, Jason-3 and Sentinel-6 Michael Freilich missions, the map is getting flatter every year.

“Most of these 20-to-30 centimeter (8-to-12 inch) changes in sea level on the open ocean are cyclic, from natural things like El Niño and La Niña, or ocean currents speeding up or slowing down,” he said. “They've always been part of the story and always will be. But what really matters to people at the coast are long-term changes in their relative sea level – that is, the height of the ocean relative to the land. Those are caused by the overall rise due to global warming, and the movement of the land. And both of those are here to stay.”

Up next: why all sea level is "local."

May 13, 2020, 10:14 PDT

Can't 'See' Sea Level Rise? You're Looking in the Wrong Place

By Alan Buis,
NASA's Jet Propulsion Laboratory

Like most beaches in North Carolina, Ocean Isle Beach experiences coastal erosion. Sea level rise accelerates and exacerbates the natural coastal erosion that's continually taking place here and at beaches around the world. Credit: NASA/JPL-Caltech

Like most beaches in North Carolina, Ocean Isle Beach experiences coastal erosion. Sea level rise accelerates and exacerbates the natural coastal erosion that's continually taking place here and at beaches around the world. Credit: NASA/JPL-Caltech

Recently I stayed in a lovely vacation rental at the eastern end of Ocean Isle Beach, a small town on North Carolina’s southern coast not far from Myrtle Beach, South Carolina. Located on a 5-mile-long (8-kilometer-long) barrier island, the community is separated from the mainland by the Atlantic Intracoastal Waterway and marsh savannas. It’s a pleasant seaside resort, with restaurants, tourist amenities, and row upon row of stilt homes, many right on the beach. My bedroom looked out over small sand dunes to the shimmering Atlantic, which, at high tide, ebbed and flowed not much farther than a stone’s throw away. From my vantage point, there were no clues that the sea here might not always be a friendly neighbor.

A short stroll along the beach quickly provided a starkly different perspective. Just a few dozen yards away, huge sandbags were piled high, guarding a number of homes from the sea. As I continued walking, I soon found myself in front of homes that were perched literally above the waves at high tide.

Ocean Isle Beach, North Carolina coastal erosion
The eastern end of Ocean Isle Beach, North Carolina, has experienced significant coastal erosion over the years that has resulted in the loss and relocation of a number of homes. Credit: NASA/JPL-Caltech
Ocean Isle Beach sandbags
Sea level in the coastal region around Ocean Isle Beach, North Carolina, has risen about 7.6 centimeters (3 inches) since the early 1980s. Sea level rise eats away at coastlines, making them more vulnerable to floods. Credit: NASA/JPL-Caltech

I passed a woman walking her dog and asked her about the homes. “There used to be two streets of houses in front of these homes,” she told me. “Now they’re oceanfront.”

It turns out the homes at the east end of Ocean Isle Beach were victims of coastal erosion, which is common at most beaches in North Carolina and throughout the world. An eroding beach can lose several feet of sand a year. Of course, storms, including hurricanes, can result in rapid beach erosion. But there’s also chronic, long-term erosion, caused by changes in the supply of sand to a beach and in relative sea level (how much the height of the ocean rises or falls relative to the land at a particular location). Records show sea level in this part of coastal North Carolina has risen about 7.6 centimeters (3 inches) since the early 1980s. According to the U.S. Global Change Research Program, coastal erosion results in U.S. coastal property losses of about a half billion dollars each year in the form of damaged structures and lost land.

It's hard to "see" sea level rise by just looking at the ocean, but its effects are very real. A new video covers some of the basics. Credit: NASA/JPL-Caltech

The case of Ocean Isle Beach illustrates a key paradox about sea level rise: since it occurs relatively slowly, it can be easy to think it’s not happening. But as oceanographer and climate scientist Josh Willis of NASA’s Jet Propulsion Laboratory in Pasadena, California, told me, if you’re not seeing it, you’re just not looking in the right place.

“Thanks to satellite and tide gauge data, we know that sea level is rising about 3.3 millimeters (0.13 inches) a year, a rate that grows by another 1 millimeter (0.04 inches) per year every decade or so,” Willis said. “Each year, global warming is currently adding about 750 gigatonnes of water to the ocean – enough to cover my home state of Texas about 1 meter (more than 3 feet) deep. We can’t really eyeball a few millimeters of sea level rise a year just by looking at the ocean because of waves, tides, etc. But we can definitely see the effects of it, both short- and long-term.”

sea level risk along U.S. Southeast coastlines
This map illustrates the levels of risk sea level rise poses along U.S. Southeast coastlines, taking into consideration the susceptibility to change and adaptation measures. The Coastal Vulnerability Index used here is based on tidal range, wave height, coastal slope, shoreline change, landform and processes, and historical rate of relative sea level rise. Credit: U.S. Global Change Research Program (2014)
National assessment of coastal vulnerability of sea-level rise: U.S. Atlantic, Pacific, and Gulf of Mexico coasts.
National assessment of coastal vulnerability of sea-level rise: U.S. Atlantic, Pacific, and Gulf of Mexico coasts. Credit: USGS

Willis said sea level rise accelerates and exacerbates the natural coastal erosion that’s continually taking place in locations like Ocean Isle Beach. “Sea level rise literally eats away at a coastline, making it more vulnerable to floods,” he said. “While floods happen naturally, it’s sea level rise that causes them to gradually begin topping natural barriers—like wetlands, mangrove forests and saltwater marshes—and even human-built barriers that typically protect coastal areas around the world from flooding. All of a sudden, that flood that you used to be protected from is now wiping you out.”

It’s the same story all over the world. You may not be able to eyeball sea level rise at your local beach, but its effects are being felt in many ways. Willis says a good rule of thumb is that every inch of sea level rise results in the loss of about 2.5 meters (100 inches) of beach, though recent studies suggest beach losses around the globe could happen even faster.

sea level graph
Not only is global sea level currently rising about 3.3 millimeters (0.13 inches) a year, but its rate of increase is also accelerating over time, by about 1 millimeter (0.04 inches) per year roughly every decade. Credit: NASA/JPL-Caltech. Data from Church and White (2006).

In many places, sea level rise has rendered sea walls erected decades ago to handle 100-year floods inadequate. Floods that used to occur once a century are now happening once a decade. You can also see the impacts of sea level rise reflected in gradual damage to infrastructure, such as the condition of coastal roads like California’s Pacific Coast Highway, which is continually battling the effects of coastal erosion.

Another phenomenon many people are experiencing more frequently but may not necessarily think is an impact of sea level rise is high tide flooding, otherwise known as “nuisance,” or “sunny day” flooding. This type of flooding, which is generally low-level, occurs year-round during high tides. Its effects range from inconveniences to the public, such as the closure of roads, businesses and schools, to long-term infrastructure damage and overwhelmed storm drains. Climate-related sea level rise is a primary contributor to high tide flooding, as is the loss of natural coastal barriers. Another contributor is the sinking of coastal lands due to adjustments related to the end of the last Ice Age, tectonics, compaction of sediments, and other dynamic processes. In the United States, high tide flooding is especially common along the East and Gulf Coasts. Over the last two decades, their frequency is up by roughly 50 percent; 100 percent if you go back three decades.

modern seawall in England
An example of a modern seawall in Ventnor on the Isle of Wight, England. In many places around the world, sea level rise has rendered sea walls erected decades ago to handle 100-year floods inadequate. Credit: Public domain
high-tide flooding in Fort Lauderdale, Florida
Fort Lauderdale, Florida, is at risk from rising sea levels and experiences high-tide flooding. Credit: Dave/Flickr Creative Commons/CC BY 2.0
nuisance street flooding in Norfolk, VA
Coastal high-tide, or "nuisance" street flooding in Norfolk, Virginia. Credit: D. Loftis/VIMS. CC BY-NC-ND 2.0

Norfolk, Virginia, is a good case in point. Norfolk, home to the world’s largest Naval base, is one of several municipalities that comprise Virginia’s Hampton Roads region, which has a population of more than 1.8 million. In the 20th Century, sea level relative to land in Norfolk rose between 4 and 5 millimeters (0.16 to 0.2 inches) a year, in part because the land in this region is sinking as it continues to adjust to the melting of the Laurentide ice sheet that covered it during the last Ice Age. Over the past couple of decades, high tide flooding here has accelerated rapidly, and now occurs about 10 days a year, causing flooding in downtown Norfolk.

“We’ve had such a large amount of sea level rise in the past century that we’re now nearing a tipping point,” said Ben Hamlington, a research scientist in JPL’s Sea Level and Ice Group. “When many coastal communities like Norfolk were established, developers took into account where historical high tide lines were, then added a safety gap to account for floods. But long-term climate change is narrowing that safety gap and a storm event is no longer required to cause significant flooding. The combination of long-term sea level rise and natural variations in sea level caused by climate cycles such as El Niño and the Pacific Decadal Oscillation (PDO) is leading to a dramatic increase in high-tide flooding events. As a result, coastal communities must now take these different natural climate cycles into account in their planning.”

Norfolk USS Harry
Most of Norfolk, Virginia, home to the largest U.S. naval base, is less than 15 feet above sea level. The city regularly experiences high-tide flooding. Credit: Tyler Folnsbee/U.S. Navy

Willis says sea level rise is causing some cities around the world to face the ultimate choice: spend huge sums of money to combat sea level rise, or literally abandon ship and move away. Last year, Indonesia announced plans to move its capital inland from Jakarta, a city of 10 million that’s sinking and challenged by sea level rise. In cities all over the world, local officials are confronting their own battles. Even relatively affluent metropolitan areas like Southern California aren’t immune. But many places, such as Bangladesh, parts of southeast Asia and small island nation states, simply don’t have the resources.

Jakarta
Panoramic view of Jakarta, Indonesia, from the Monas National Monument. The capital city of 10 million is sinking and challenged by sea level rise. Credit: BxHxTxCx / CC BY-SA

Willis says California and the U.S. West Coast have been spared the worst effects of sea level rise over the past 20 years. But that may be about to change.

“Over the past 15 to 20 years, we’ve been watching warm waters in the Pacific Ocean move away from the West Coast due to a shift in the PDO, a long-term ocean fluctuation pattern that’s similar to the El Niño/La Niña cycles but that operates on a much larger scale, waxing and waning about every 20 to 30 years,” he said. “This has served to counteract the effects of global sea level rise, so that along the U.S. Pacific Coast, we’ve seen almost no sea level rise over that time. But those days are over. Since the major El Niño of 2015-16, the PDO has shifted and the West Coast is likely to see faster-than-average sea level rise in the next 20 years. We’re already beginning to see this. California, in particular, needs to prepare. We could see increases up to 1 centimeter (0.4 inch) a year, more than three times the global rate.”

Laguna Beach, California
Coastal communities along the U.S. West Coast like Laguna Beach, California, are likely to see faster-than-average sea level rise in the next 20 years. Credit: Patrick Pelster / CC BY-SA 3.0 DE

Such a rate of sea level rise would equate to more than 20 centimeters (8 inches) in the next two decades. To put that into perspective, over the past century, sea level along California’s coast has gone up about 23 centimeters (9 inches). This will pose major challenges for many parts of the Golden State, from San Francisco and San Diego Bays, to the Ports of Long Beach and Los Angeles, and cities in coastal Orange County, to name a few. “We think of California as having a lot of cliffs,” says Willis. “It does, but in between, there are lots of low-lying areas where sea level rise is going to cause problems.”

Whether you want to see it or not, sea level rise is a global problem. And that’s no day at the beach.

May 6, 2020, 10:16 PDT

Fire and Ice: Why Volcanic Activity Is Not Melting the Polar Ice Sheets

By Alan Buis,
NASA's Jet Propulsion Laboratory

Mount Waesche is a 10,801-foot-high (3,292 meters) possibly active volcano at the southern end of the Executive Committee Range in Marie Byrd Land, Antarctica. Credit: NASA/Michael Studinger

Mount Waesche is a 10,801-foot-high (3,292 meters) possibly active volcano at the southern end of the Executive Committee Range in Marie Byrd Land, Antarctica. Credit: NASA/Michael Studinger

Few natural phenomena are as impressive or awesome to behold as glaciers and volcanoes. I’ve seen both with my own eyes. I’ve marveled at the enormous power of flowing ice as I trekked across a glacier on Washington’s Mount Rainier — an active, but dormant, volcano. And I’ve hiked a rugged lava field on Hawaii’s Big Island alone on a moonless night to witness the surreal majesty of a lava stream from Kilauea volcano spilling into the sea — its orange-red lava meeting the waves in billowing steam — while still more glowing ribbons of lava snaked down the mountain slopes behind me.

There are many places on Earth where fire meets ice. Volcanoes located in high-latitude regions are frequently snow- and ice-covered. In recent years, some have speculated that volcanic activity could be playing a role in the present-day loss of ice mass from Earth’s polar ice sheets in Greenland and Antarctica. But does the science support that idea?

Illustration of flowing water under the Antarctic ice sheet
Illustration of flowing water under the Antarctic ice sheet. Blue dots indicate lakes, lines show rivers. Marie Byrd Land is part of the bulging "elbow" in the left center of the image. Credit: NSF/Zina Deretsky

In short, the answer is a definitive “no,” though recent studies have shed important new light on the matter. For example, a 2017 NASA-led study by geophysicists Erik Ivins and Helene Seroussi of NASA’s Jet Propulsion Laboratory added evidence to bolster a longstanding hypothesis that a heat source called a mantle plume lies deep below Antarctica's Marie Byrd Land, explaining some of the melting that creates lakes and rivers under the ice sheet. While the study may help explain why the ice sheet collapsed rapidly in an earlier era of rapid climate change and why it’s so unstable today, the researchers emphasized that the heat source isn't a new or increasing threat to the West Antarctic ice sheet, but rather has been going on over geologic timescales, and therefore represents a background contribution to the melting of the ice sheet.

I checked in with Ivins and Seroussi to get a deeper understanding of this question, which our readers frequently ask about. Here's what I learned…

Greenland Has a Long-Departed “Hot Spot” but Is Now Quiet

Since 2002, the U.S./German Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions have recorded a rapid loss of ice mass from Greenland — at a rate of approximately 281 gigatonnes per year.

Greenland mass variation since 2002
Data from the U.S./German GRACE and GRACE Follow-On satellite missions show the Greenland ice sheet is losing ice mass at a rate of approximately 281 gigatonnes per year since 2002. Credit: NASA

There’s plenty of evidence of volcanism in regions now covered by the Greenland ice sheet and the mountains around it, but this volcanic activity occurred in the distant past. Many of Greenland’s mountains are eroded flood basalts — high-volume lava eruptions that cover broad regions. Flood basalts are the biggest type of lava flows known on Earth.

A glacier between mountains in Greenland's Geikie Peninsula
A glacier between mountains on Greenland's Geikie Peninsula. The mountains here consist mostly of flood basalts formed during the opening of the North Atlantic Ocean millions of years ago. Credit: NASA/Michael Studinger

But volcanic activity isn’t responsible for the current staggering loss of Greenland’s ice sheet, says Ivins. There are no active volcanoes in Greenland, nor are there any known mapped, dormant volcanoes under the Greenland ice sheet that were active during the Pliocene period of geological history that began more than 5.3 million years ago (volcanoes are considered active if they’ve erupted within the past 50,000 years). In fact, he says, the history of the Greenland ice sheet is probably more connected to atmospheric and ocean heat than it is to heat from the solid Earth. Ten million years ago, there was actually very little ice present in Greenland. The whole age of ice sheet waxing and waning in the Northern Hemisphere didn’t really get going until about five million years ago.

This visualization shows the Greenland geothermal heat flux map, the track of the Iceland hotspot through Greenland, and the plate tectonic motion of Greenland over the hotspot during the past 100 million years. Credit: NASA’s Scientific Visualization Studio

While there are no active volcanoes in Greenland, scientists are confident a “hot spot” — an area where heat from Earth’s mantle rises up to the surface as a thermal plume of buoyant rock — existed long ago beneath Greenland because they can see the residual heat in Earth’s crust, Ivins says. While mantle plumes can drive some forms of volcanoes, Ivins says they aren’t a factor in the current melting of the ice sheet. Researchers hypothesize however that this residual heat may drive the flow of the Northeast Greenland Ice Stream, which penetrates hundreds of kilometers inland (an ice stream is a faster-flowing current of ice within a larger and more stagnant ice sheet). Recent modeling experiments show that if enough residual heat is present, it can initiate an ice stream. GPS measurements also provide evidence that a hot spot once existed beneath Greenland.

Northeast Greenland Ice Stream
Ice in the Northeast Greenland Ice Stream can travel more than 1,640 feet (500 meters) each year. Credit: NASA's Goddard Space Flight Center

That hot spot subsequently moved, however, and now lies beneath Iceland — home to about 130 volcanoes, of which roughly 30 are active. The hot spot is at least partially responsible for the island’s high volcanic activity. Iceland also lies along the tectonically active Mid-Atlantic Ridge.

Overview of the second fissure on Iceland's Fimmvörðuháls volcano
Overview of the second fissure on Iceland’s Fimmvörðuháls volcano, close to Eyjafjallajökull volcano, as the lava flows down toward the north, turning snow into steam. Credit: Boaworm / CC BY

Antarctica Has Volcanoes, but There's No Link to its Current Ice Loss

Antarctica mass variation since 2002
Data from the U.S./German GRACE and GRACE Follow-On satellite missions show the Antarctic ice sheet is losing ice mass at a rate of approximately 146 gigatonnes per year since 2002. Credit: NASA

The GRACE missions have also observed a rapid loss of ice mass in Antarctica, at a rate of approximately 146 gigatonnes per year since 2002. Unlike Greenland, however, there’s substantial evidence of volcanoes under the Antarctic Ice Sheet, some of which are currently active or have been in the recent geologic past. While the exact number of volcanoes in Antarctica is unknown, a recent study found 138 volcanoes in West Antarctica alone. Many of the active volcanoes are located in Marie Byrd Land. However, there’s no evidence of a dramatic volcanic eruption in Antarctica in the recent geologic past. Seroussi says details about the volcanism of many parts of Antarctica (particularly in East Antarctica) remain uncertain, both because they’re covered by ice and because their remoteness makes surveying them difficult.

Map of Antarctica showing the distribution of volcanoes aged between c. 11 Ma and present. Only a small number are active.
Map of Antarctica showing the distribution of volcanoes aged between c. 11 Ma (million years) and present. Only a small number are active. Credit: Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)
Locations of recently discovered West Antarctic volcanoes
Map of the location of cone-shaped structures (circles) identified from the British Antarctic Survey's Bedmap2 ice thickness and subglacial topographic model of Antarctica (greyscale background) across the West Antarctic Rift System. The color of the circles represents the degree of confidence the researchers have that the cones are subglacial volcanoes, and the circle size is proportional to the size of the cone’s base diameter. Circles with black rims represent volcanoes that have been confirmed in other studies (LeMasurier et al. 1990; Smellie & Edwards 2016); generally those with tips that protrude above the ice surface. Credit: Attribution 3.0 Unported (CC BY 3.0)

Multiple additional lines of evidence point to Antarctica’s past and present volcanism. For example, topographic maps of the bedrock beneath the Antarctic ice sheet give scientists clues to suspected volcanic locations. Analyses of volcanic rock samples reveal numerous volcanic eruptive events within the last 100,000 years, as do ash layers in ice cores. In their 2017 study of Marie Byrd Land, Seroussi and Ivins estimated the intensity of the heat produced by the hypothesized mantle plume by studying the meltwater produced under the ice sheet and its motion by measuring changes in the elevation of the ice surface.

Antarctica's Bedrock

These images depict the differences between Antarctica's ice sheet with its underlying topography. Click and drag the white bar to compare the images. (Vertical scale has been magnified by a factor of 17 to make terrain features such as mountains and valleys more visible.)

The topography map, called Bedmap2, was compiled by the British Antarctic Survey and incorporates millions of new measurements, including substantial data sets from NASA's ICESat satellite and an airborne mission called Operation IceBridge. Credit: NASA's Goddard Space Flight Center
Ice core
The dark band in this ice core from West Antarctica is a layer of volcanic ash that settled on the ice sheet approximately 21,000 years ago. Credit: Heidi Roop, National Science Foundation (NSF)

An intriguing paper by Loose et al. published in Nature Communications in 2018 provides additional evidence. The researchers measured the composition of isotopes of helium detected in glacial meltwater flowing from the Pine Island Glacier Ice Shelf. They found evidence of a source of volcanic heat upstream of the ice shelf. Located on the West Antarctic ice sheet, Pine Island Glacier is the fastest melting glacier in Antarctica, responsible for nearly a quarter of all Antarctic ice loss. By measuring the ratio between helium’s two naturally-occurring isotopes, scientists can tell whether the helium taps into Earth’s hot mantle or is a product of crust that is relatively passive tectonically.

The team found the helium originated in Earth’s mantle, pointing to a volcanic heat source that may be triggering melting beneath the glacier and feeding the water network beneath it. However, the researchers concluded that the volcanic heat is not a significant contributor to the glacial melt observed in the ocean in front of Pine Island Glacier Ice Shelf. Rather, they attributed the bulk of the melting to the warm temperature of the deep-water mass Pine Island Glacier flows into, which is melting the glacier from underneath.

Antarctica's Pine Island Glacier meets the ocean.
Antarctica’s Pine Island Glacier meets the ocean. Credit: Galen Dossin, NSF

Seroussi notes the changes happening now, especially in West Antarctica, are along the coast, which suggests the changes taking place in the ice sheet have nothing to do with volcanism, but are instead originating in the ocean. Ice streams reaching inland begin to flow and accelerate as ice along the coast disappears.

In addition, Seroussi says the tectonic plate that Antarctica rests upon is one of the most immobile on Earth. It’s surrounded by activity, but that activity also tends to keep it locked in position. There’s no reason to believe it would change today to impact the melting of the Antarctic ice sheet.

So, in conclusion, while Antarctica’s known volcanism does cause melting, Ivins and Seroussi agree there’s no connection between the loss of ice mass observed in Antarctica in recent decades and volcanic activity. The Antarctic ice sheet is at least 30 million years old, and volcanism there has been going on for millions of years. It's having no new effect on the current melting of the ice sheet.

March 10, 2020, 13:38 PDT

How Climate Change May Be Impacting Storms Over Earth's Tropical Oceans

By Alan Buis,
NASA's Jet Propulsion Laboratory

Hurricane Lorenzo moving through the eastern North Atlantic Ocean, as seen from NASA's Terra satellite. Credit: NASA Worldview, Earth Observing System Data and Information System (EOSDIS).

Hurricane Lorenzo moving through the eastern North Atlantic Ocean, as seen from NASA's Terra satellite. Credit: NASA Worldview, Earth Observing System Data and Information System (EOSDIS).

When NASA climate scientists speak in public, they’re often asked about possible connections between climate change and extreme weather events such as hurricanes, heavy downpours, floods, blizzards, heat waves and droughts. After all, it seems extreme weather is in the news almost every day of late, and people are taking notice. How might particular extreme weather and natural climate phenomena, such as El Niño and La Niña, be affected by climate change, they wonder?

There’s no easy answer, says Joao Teixeira, co-director of the Center for Climate Sciences at NASA’s Jet Propulsion Laboratory in Pasadena, California, and science team leader for the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite. “Within the scientific community it’s a relatively well-accepted fact that as global temperatures increase, extreme precipitation will very likely increase as well,” he says. “Beyond that, we’re still learning.”

“Within the scientific community it’s a relatively well-accepted fact that as global temperatures increase, extreme precipitation will very likely increase as well. Beyond that, we’re still learning.”
- Joao Teixeira

While there’s not yet a full consensus on the matter, in recent years a body of evidence linking extreme weather with climate change has begun to emerge. Evidence from satellites, aircraft, ground measurements and climate model projections are increasingly drawing connections. Quantifying those interconnections is a big challenge.

“All our available tools have pros and cons,” says Teixeira. “Rain gauges, for example, provide good measurements, but they’re local and spread far apart. In contrast, satellites typically measure climate variables (such as precipitation, temperature and humidity) indirectly and don’t yet have long enough data records to establish trends, though that’s beginning to change. In addition, representing small-scale processes of the atmosphere that are key to extreme weather events in climate models, such as turbulence, convection and cloud physics, is notoriously difficult. So, we’re in a bit of a conundrum. But great progress is being made as more studies are conducted.”

A simple analogy describes how difficult it is to attribute extreme weather to climate change. Adding fossil fuel emissions to Earth’s atmosphere increases its temperature, which adds more energy to the atmosphere, supercharging it like an athlete on steroids. And just as it’s difficult to quantify how much of that athlete’s performance improvement is due to steroid use, so too it’s difficult to say whether extreme weather events are definitively due to a warmer atmosphere.

Are Supercharged Atlantic Hurricane Seasons a Case in Point?

Take hurricanes, for example. A hot topic in extreme weather research is how climate change is impacting the strength of tropical cyclones. A look at the 2019 Atlantic hurricane season provides a case in point.

After a quiet start to the 2019 season, Hurricane Dorian roared through the Atlantic in late August and early September, surprising many forecasters with its unexpected and rapid intensification. In just five days, Dorian grew from a minimal Category 1 hurricane to a Category 5 behemoth, reaching a peak intensity of 185 miles (295 kilometers) per hour when it made landfall in The Bahamas. In the process, Dorian tied an 84-year-old record for strongest landfalling Atlantic hurricane and became the fifth most intense recorded Atlantic hurricane to make landfall, as measured by its barometric pressure.

visible hurricane dorian
Hurricane Dorian as seen by the four visible/near-infrared channels of the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's Aqua satellite at 2 p.m. EDT (11 a.m. PDT) on Sept. 1, 2019, as the storm made landfall in The Bahamas. At the time of landfall, Dorian had reached its peak intensity of 185 miles (295 kilometers) per hour, tying an 84-year-old record for strongest landfalling Atlantic hurricane. Credit: NASA/JPL-Caltech
false-color infrared hurricane dorian
A false-color infrared image of Hurricane Dorian, as seen by the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's Aqua satellite at 2 p.m. EDT (11 a.m. PDT) on Sept. 1, 2019. Hurricanes are large collections of severe, deep thunderstorms. Purple shades denote the coldest cloud top temperatures and most severe convective activity. Blues and greens show warmer areas with less rain clouds, while oranges and reds represent mostly cloud-free air. Each square pixel represents the measurements from a 10-by-10-mile (16-by-16-kilometer) area. Credit: NASA/JPL-Caltech

Two weeks later the remnants of Tropical Storm Imelda swamped parts of Texas under more than 40 inches (102 centimeters) of rain, enough to make it the fifth wettest recorded tropical cyclone to strike the lower 48 states. Fueled by copious moisture from a warm Gulf of Mexico, the slow-moving Imelda’s torrential rains and flooding wreaked havoc over a wide region.

Then in late September, Hurricane Lorenzo became the most northerly and easterly Category 5 storm on record in the Atlantic, even affecting the British Isles as an extratropical cyclone.

Earth’s atmosphere and oceans have warmed significantly in recent decades. A warming ocean creates a perfect cauldron for brewing tempests. Hurricanes are fueled by heat in the top layers of the ocean and require sea surface temperatures (SSTs) greater than 79 degrees Fahrenheit (26 degrees Celsius) to form and thrive.

Since 1995 there have been 17 above-normal Atlantic hurricane seasons, as measured by NOAA’s Accumulated Cyclone Energy (ACE) Index. ACE calculates the intensity of a hurricane season by combining the number, wind speed and duration of each tropical cyclone. That’s the largest stretch of above-normal seasons on record.

So while there aren’t necessarily more Atlantic hurricanes than before, those that form appear to be getting stronger, with more Category 4 and 5 events.

NASA Research Points to an Increase in Extreme Storms Over Earth’s Tropical Oceans

What does NASA research have to say about extreme storms? One NASA study from late 2018 supports the notion that global warming is causing the number of extreme storms to increase, at least over Earth’s tropical oceans (between 30 degrees North and South of the equator).

A team led by JPL’s Hartmut Aumann, AIRS project scientist from 1993 to 2012, analyzed 15 years of AIRS data, looking for correlations between average SSTs and the formation of extreme storms. They defined extreme storms as those producing at least 0.12 inches (3 millimeters) of rain per hour over a certain-sized area. They found that extreme storms formed when SSTs were hotter than 82 degrees Fahrenheit (28 degrees Celsius). The team also saw that for every 1.8 degrees Fahrenheit (1 degree Celsius) that SST increased, the number of extreme storms went up by about 21 percent. Based on current climate model projections, the researchers concluded that extreme storms may increase 60 percent by the year 2100.

Thanks to weather satellites, scientists have identified possible correlations between the extremely cold clouds seen in thermal infrared satellite images (called deep convective clouds) and extreme storms observed on the ground under certain conditions, especially over the tropical oceans. When precipitation from these clouds hits the top of Earth’s lowest atmospheric layer, the troposphere, it produces torrential rain and hail.

AIRS can’t measure precipitation directly from space, but it can measure the temperature of clouds with extraordinary accuracy and stability. Its data can also be correlated with other climate variables such as SSTs, for which scientists maintain long data records.

To determine the number of extreme storms, Aumann’s team plotted the number of deep convective clouds each day against measurements of sea surface temperature. They found that the number of these clouds correlated with increases in sea surface temperature.

The results of this study reflect a long line of AIRS research and three previously published papers. The researchers say large uncertainties and speculations remain regarding how extreme storms may change under future climate scenarios, including the possibility that a warming climate may result in fewer but more intense storms. But the results of this study point to an intriguing direction for further research.

What Lies Ahead?

Aumann is confident future studies will reveal additional insights into how severe storms detected as individual deep convective clouds coalesce to form tropical storms and hurricanes. He notes that if you look at these clouds over the global ocean, they frequently occur in clusters.

“AIRS sees hurricanes as hundreds of these clusters,” he said. “For example, it saw Hurricane Dorian as a cluster of about 150 deep convective clouds, while Hurricane Katrina contained about 500. If you look at a weather satellite image, you’ll see the severe storms that make up a hurricane are not actually contiguous. In fact, they’re uncannily similar to the stars within the spiral arms of a galaxy. It’s one severe thunderstorm after another, each dumping a quantity of rain on the ground.

“AIRS has 2,400 different frequency channels, so it’s a very rich data set,” he said. “In fact, there’s so much data, our computer capabilities aren’t able to explore most of it. We just need to ask the right questions.”