TOPIC | Antarctica

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.”

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.

April 10, 2019, 13:30 PDT

Arctic and Antarctic Sea Ice: How Are They Different?

From NASA's Global Climate Change Website

Credit: NASA's Goddard Space Flight Center

Credit: NASA's Goddard Space Flight Center

We often get questions from readers about Earth’s sea ice in the Arctic and the Antarctic, and the differences between those areas. Arctic sea ice has declined over the past five decades, while Antarctic sea ice has increased, and then declined. Why do they behave differently?

How They’re Different

The primary difference between the Arctic and Antarctica is geographical. The Arctic is an ocean, covered by a thin layer of perennial sea ice and surrounded by land. ("Perennial" refers to the oldest and thickest sea ice.) Antarctica, on the other hand, is a continent, covered by a very thick ice cap and surrounded by a rim of sea ice and the Southern Ocean.

The Arctic Ocean is very deep and closely linked with the climate systems around it, making it more sensitive to climate changes than Antarctica.

During the centuries of human exploration in the Arctic, sea ice covered the Arctic Ocean well year-round, up until recent decades. But satellite observations show that Arctic sea ice has been declining in extent*, thickness and volume since 1979.1 Average Arctic sea ice extent is at its lowest since 1850.

During the summer melt season, the sea ice’s edge retreats toward the North Pole, only to re-grow during the Arctic winter. As a result of ongoing warming driven by human activities, the trend toward summer sea ice loss (from July to September, followed by a winter re-growth) continues.

Recent research suggests that there is a relationship between Arctic sea ice losses and the human burning of fossil fuels in all months.2 Aerosols (tiny particles suspended in the atmosphere) tied to human activities have offset some of the Arctic sea ice extent loss trend; a reduction in aerosol pollution will likely see a sea ice loss acceleration.3 Ice loss at the sea ice’s margins** results in winds driving warmer water beneath the Arctic sea ice, increasing the amount of heat the Arctic Ocean stores 4 and priming conditions for further sea ice loss.

A figure showing current Arctic sea ice extent can be found here.

Antarctic Sea Ice

Antarctic sea ice expands during the winter, only to melt back largely to the continent’s edge in summer.

Antarctic sea ice extent is currently below the long-term average of all decades prior since 1979. Previously, Antarctic sea ice extent had been above that long-term average due to long-term, large-scale wind circulation patterns that drove sea ice away from Antarctica5, making room for more sea ice to form nearer to the continent.6 Climate models, or computer simulations that incorporate all the factors that affect Earth’s climate, predicted this behavior.7 These long-term wind patterns reversed several years ago, resulting in a significant sea ice decline surrounding Antarctica. Values since then have been hovering around the average of all years prior in the satellite record. A figure showing current Antarctic sea ice extent can be found here.

arctic and antarctic sea ice trend
Arctic sea ice extent underwent a strong decline from 1979 to 2012 and Antarctic sea ice underwent a slight increase, although some regions of the Antarctic experienced strong declining trends in sea ice extent. The solid lines indicate 12-month running averages, while the dotted lines indicate the overall trend. Units of extent are shown as standard deviations, which refers to the extent of change from the average. (Source: National Snow and Ice Data Center)

Why Sea Ice Matters

Some of the questions we receive ask why we should care about the polar regions. These regions are very important in regulating global temperature. Because sea ice has a bright surface, 50-70 percent of incoming energy is reflected back into space. As sea ice melts in the summer, it exposes the dark ocean surface. Instead of reflecting 50-70 percent of the sunlight, it absorbs 90 percent of the sunlight. As the ocean warms, global temperatures rise further.

Also, what happens in the polar regions doesn’t stay in those regions. Their changes affect global temperatures and can even change ocean circulation. Earth’s sea ice is very attuned and responsive to even small changes in global surface and ocean temperatures.

Learn More


  1. New Year Lows Once Again, NSIDC; Kwok, R. (2018), Arctic sea ice thickness, volume, and multiyear ice coverage: Losses and coupled variability (1958 – 2018). Environ. Res. Lett. 13 (2018) 105005; and
    Arctic Sea Ice Volume Anomaly, Polar Ice Center
  2. Julienne Stroeve and Dirk Notz, Changing state of Arctic sea ice across all seasons, Environmental Research Letters, Volume 13, Number 10
  3. B. L. Mueller, Attribution of Arctic Sea Ice Decline from 1953 to 2012 to Influences from Natural, Greenhouse Gas, and Anthropogenic Aerosol Forcing,
  4. Mary-Louise Timmermans, John Toole and Richard Krishfield, Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins, Science Advances 29 Aug 2018: Vol. 4, no. 8
  5. All About Sea Ice, NSIDC
  6. Gerald A. Meehl et al, Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability,
  7. A Tale of Two Poles, Earth Observatory, 2014

*Sea ice extent is a measurement of the area of ocean where there is at least some sea ice.

**Margins are transition regions between the ice-covered and ice-free portions of the ocean.