August 27, 2009, 17:00 PDT

What goes around comes around

Orbits and climate change

James Croll pioneered the study of how the Earth's orbit affects its climate.

From Erik Conway,
NASA Jet Propulsion Laboratory

John Tyndall’s discovery of greenhouse gases in 1859 (see "All about hot air") was just one of a whole series of efforts to study the physics of Earth’s climate during the 19th century. Another important figure was Scotsman James Croll, who argued that changes in the Earth’s orbit caused ice ages.

Croll was born on a farm on January 2, 1821, in Little Whitfield, Scotland. Before turning to science, he was a jack-of-all-trades: by turns a millwright, tea merchant, innkeeper, and caretaker at Andersonian College and Museum in Glasgow. It was this last job that exposed him to a very well-stocked scientific library, where he began reading and thinking about Earth’s history.

In 1864, Croll published a theory of the role Earth’s orbit might play in causing climate change, which has since been called the "Astronomical Theory of Climate Change”. He focused on the eccentricity of Earth’s orbit (how much the orbit varies from a perfect circle) and its precession (how much the planet ‘wobbles’ around its vertical axis). Croll worked out that the amount of incoming sunlight could vary by as much as 20 percent when these orbital characteristics both reached extremes — quite enough to create an ice age. But because of the part played by the Earth’s precession, he thought that as one hemisphere was in the grips of an ice age, the other hemisphere would be warmer (in the midst of a so-called “interglacial” period). According to his calculations, this glacial/interglacial cycle took about 100,000 years to complete. Croll accepted the conventional view among European geologists of the day that the Earth was about 98 million years old (in fact, we know today that it’s actually about 4.5 billion years old). So he was arguing, in short, that there had been hundreds of ice ages in Earth’s history.

Croll promoted his research aggressively, publishing a number of articles before completing an 1875 masterpiece, “Climate and Time in their Geological Relations”. But the Astronomical Theory was never accepted as fact during his lifetime, because of the lack of geological evidence for hundreds of ice ages at the time. It wasn’t until the 1970s that geologists, armed with scientific evidence such as deep-sea sediment cores that wasn’t available to Croll, finally accepted that orbital mechanics did indeed affect the Earth’s climate.

Erik is a historian based at NASA’s Jet Propulsion Laboratory in Pasadena, California.

August 25, 2009, 17:00 PDT

Pick of the pics

Altamaha River delta, Georgia coast

Courtesy of NASA/Jet Propulsion Laboratory/University of Edinburgh.

Courtesy of NASA/Jet Propulsion Laboratory/University of Edinburgh.

The Altamaha River delta found at the mouth of Georgia’s largest river has a long history of agricultural development, which dates back to the founding of the Georgia Colony in 1733. In this image, taken by NASA’s Airborne Synthetic Aperture Radar (AIRSAR) during a 1994-1995 data collection campaign, the outlines of long-lost plantation rice fields, canals, dikes and other inlets are clearly defined. Salt marshes are shown in red, while dense cypress and live oak tree canopies can be seen in yellow-green hues. The plantation system ended with the American Civil War of the 1860s. Today, the delta attracts flocks of endangered birds such as the American oystercatcher, thanks to its abundant food supply, shelter and nesting grounds.

August 21, 2009, 17:00 PDT

It's a bug's life

Adapting to new climes

Insects might not be as sexy as polar bears. But they are an incredibly important cog in the ecological wheel — they are the most diverse group of animals on Earth, represent more than half of all known living organisms, and pollinate nearly 80 percent of the world's crops. According to a recent article from the National Science Foundation (NSF), they could also be severely impacted by climate change.

Insects are invertebrates and cold-blooded; they lack internal temperature controls so their body temperature approximates that of their environment. This makes them "great little thermometers" according to biologist Jessica Hellman of the University of Notre Dame, who is studying the growth and survival rates of insects subjected to changes in environment. It also makes them particularly susceptible to global warming.

The question biologists are trying to grapple with is this: Will insects become "trapped" in habitats that can no longer support them as temperatures rise and climate change progresses? Will some species be mobile enough to enable them to migrate to cooler climes and continue to survive? Hellman is currently surveying thousands of genes in different butterfly species to see which ones are turned 'on' or 'off' by climate change, and ultimately if there is a genetic basis to the fact that some insect species are more tolerant to climate change than others.

It may sound strange to some people to think of relocating insects to new homes. But this "managed relocation" is exactly what Hellman and colleagues are looking into. They are working to develop tools that will fold in ecological and social data to help decision makers in the event that insects, animals and plants need to be relocated because of climate change.

August 19, 2009, 17:00 PDT

A perfect storm

Doing the numbers

Hurricane activity on the up?

Over the past 10 years, an average of 26 hurricanes and tropical storms have formed in the Atlantic Ocean each year. Yet despite the recent surge in tropical cyclone activity, this peak is nothing new according to a paper just published in Nature. Climate scientist Michael Mann and colleagues, who analyzed hurricane data from the past 1,500 years, say that hurricane activity was just as high, if not higher, around 1000 A.D.

In medieval times there were of course no space satellites to track storms, so Mann and his co-authors used sediment deposits in coastal regions to search for evidence of hurricanes that make landfall. They also cross-checked their results using statistical techniques which, by taking into account climate changes in the past, can predict how many Atlantic tropical cyclones occurred. What they found was that the medieval peak in hurricane activity coincided with periods of higher sea surface temperatures. Warmer waters are vital for providing the energy that nourishes hurricanes, and sea surface warming has been implicated in increased hurricane activity before (here and here, for example).

There is still debate amongst hurricane researchers as to whether the recent spike in activity is a real climate effect or simply a reflection of the fact that we’re getting better at counting storms, especially short-lived ones. Mann says that his team’s analysis takes into account potential inaccuracies in the number of hurricanes counted in the past, and yet still points towards a peak in activity over the past decade. While the scientific storm rages on, if global warming continues to warm our oceans, we could very well expect to see more hurricanes in the future.

August 17, 2009, 17:00 PDT

Pick of the pics

Malaspina Glacier, Alaska

Courtesy of NASA/Goddard Space Flight Center, Japan's Ministry of Economy, Trade and Industry, Japan's Earth Remote Sensing Data Analysis Center, the Japan Resources Observation System, and the U.S./Japan ASTER Science Team.

Courtesy of NASA/Goddard Space Flight Center, Japan's Ministry of Economy, Trade and Industry, Japan's Earth Remote Sensing Data Analysis Center, the Japan Resources Observation System, and the U.S./Japan ASTER Science Team.

This picture of Malaspina Glacier, Alaska, was taken in June 2001 by NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument. A recent report from the U.S. Geological Survey, which has tracked the state of glaciers in the Pacific Northwest and Alaska over the past 50 years, shows that they have shrunk dramatically over the last couple of decades. The South Cascade Glacier in Washington, for example, has lost nearly half its volume and a quarter of its mass since 1958. These long periods of record give us clues to the climate shifts (higher worldwide temperatures) that are likely driving glacier change.

August 13, 2009, 17:00 PDT

All about hot air

Paving the way

John Tyndall (1820-1893).<br>Drawing by Roger Kammerer.
John Tyndall (1820-1893).
Drawing by Roger Kammerer.

From Erik Conway,
NASA Jet Propulsion Laboratory

One of the burning questions (pun intended!) in the late 18th and early 19th centuries was why the Earth is so warm. A number of scientists, including the famous French polymath, Joseph Fourier, had calculated that it should be far colder than it actually is — cold enough, in fact, to be a frozen ball. And some of them had speculated that something about the atmosphere must be responsible for the Earth’s most fortunate, mainly unfrozen condition. The first person to show experimentally what the atmosphere did was an Irish physicist, John Tyndall.

Tyndall was born in 1820 in Leighlin Bridge, Ireland. Having finished a Ph.D. in mathematics at the University of Marburg, Germany, he took a job at the Royal Institution of Great Britain, a prestigious research organization, in 1853. (A man of many talents, he also happened to be a pioneering scientific mountaineer, climbing a variety of European mountains to study their glaciers.) Tyndall became interested in how both heat and magnetism were transmitted through various substances and, in 1859, turned his focus to gases. That May, he announced that he had found huge differences in the ability of various gases to transmit heat.

What he had discovered was that oxygen, nitrogen and hydrogen had almost no impact on heat — they were transparent to it. But carbon dioxide, ozone and “aqueous vapor,” as Tyndall called water vapor, all had a big impact on the amount of heat they let through. Of these, water vapor trapped the most heat. Without this curious characteristic, he wrote, “the warmth of our fields and gardens would pour itself unrequited into space, and the sun would rise upon an island held fast in the iron grip of frost.” It was these gases and vapors that ‘blanketed’ the Earth and kept it warm.

He also suspected that changing amounts of these gases in the atmosphere were responsible for “all the mutations of climate which the researches of geologists reveal...” In other words, they might have caused the ice ages. Though Tyndall was not interested in the modern problem of global warming, his work is hugely relevant today. It took nearly another century before anyone was able to demonstrate that humans were increasing the amount of carbon dioxide in the Earth’s atmosphere, forcing the world to slowly warm.

Erik is a historian based at NASA’s Jet Propulsion Laboratory in Pasadena, California.

August 11, 2009, 17:00 PDT

Don't forget the aerosols!

Note to policymakers

Don't forget the aerosols!

From Adam Voiland,
NASA Earth Science News Team

Debate is ratcheting up over a sweeping American climate and energy bill that, if it becomes law, would limit emissions of greenhouse gases through a complicated cap-and-trade system. H.R.2454 — a.k.a. the American Clean Energy and Security Act of 2009 — is currently being debated in the United States Congress and aims to limit emissions by 17 percent by 2020. Dr. Nadine Unger, a scientist at NASA's Goddard Institute for Space Studies, has a bit of advice for lawmakers grappling with the details of the thousand-plus page bill: don't forget about the aerosols!

Though they've long played second fiddle to greenhouse gases in discussions of climate science, these tiny airborne particles play a significant role in the climate system, and they're the subject of intense research at NASA.

What's critical to understand about aerosols is that they can either warm or cool the climate depending on their shape, chemical composition and other characteristics. Some types, most notably sulfates from the combustion of coal, reflect incoming solar radiation and actually have a cooling effect on Earth's climate. Others — notably black carbon which comes from vehicle and ship diesel fumes, burning vegetation, and the use of peat and wood chips for fuel on cooking stoves — absorb sunlight and thus have a warming effect.

Yet most policy assessments are carbon-dioxide-centric. "Aerosols are completely neglected in most policy assessments and some climate models too," said Unger, who recently published a new study that urges climate science policymakers to pay heed to the impact of aerosol particles.

Unger's study, explained in detail here and in more accessible language by one of her co-authors here, compares the climatic impact of the transportation sector to the power generation sector. Her conclusion: reducing transportation emissions will more effectively slow climate change than reducing power sector emissions in the short term.

Why? The aerosols, of course. Power generation produces sulfates that actually offset the warming influence of the carbon dioxide released. Motorized vehicles, especially those that run on diesel, are doubly bad: they produce black carbon that exacerbates warming in addition to loads of carbon dioxide.

Adam is based at NASA’s Goddard Space Flight Center outside Washington, D.C.

August 10, 2009, 17:00 PDT

With a little help...

Thunder and lightning, not so frightening

Lightning strikes twice?

Lightning strikes twice?

Every Fourth of July, Americans gather together to celebrate Independence Day. Since the first anniversary of the event in 1777, fireworks have been an integral part of the festivities and today crowds of people flock to stadiums, parks and gather in their backyards to enjoy the show.

Spurred on by Fourth of July celebrations, one of our followers of our @EarthVitalSigns Twitter stream asked me whether or not fireworks could potentially trigger thunderstorms when they are shot into clouds. I posed the question to Dr. Matt Rogers, a member of NASA’s CloudSat mission (which studies the structure of clouds and their properties from space). In short, the answer is “kind of”, but you need slightly more than 140 characters to answer the question….

“The only difference between a cumulonimbus cloud and a thunderstorm is the presence of lightning in the latter,” says Rogers. “Lightning is caused by a buildup of electrical charge inside a cloud, which eventually breaks down the natural electrical resistance of the air in and around the cloud. What causes this buildup of charge is still an area of active research, but the key point is that it takes a lot of charge disparity to create lightning — much more than any amount of exploding fireworks could possibly contribute.”

However, in a developing thunderstorm, where a lot of charge has already naturally built up, the presence of fireworks or smoke could potentially lower the resistance of the air enough to form lightning, Rogers says. “It would depend on the makeup of the pyrotechnic charge in the firework where in the cloud a lightning bolt might form.” In this case, the firework would not so much be creating the lightning as modifying when or where it will occur. “In this scenario, you'd probably still have a thunderstorm even without the fireworks, but with the fireworks, you might be creating an easier path to ground for the lightning to follow, which would fall under the rubric of 'helping start a thunderstorm'.”

A lot of research has been conducted using special “lightning rockets” that use rocket launchers to trigger lightning strikes. Fireworks aren’t terribly different from these devices, except for the fact that the scientists are prepared for the resulting lightning strike a lot better than a Fourth of July crowd would be.

August 7, 2009, 17:00 PDT

Golden state at risk

California adapting to climate change

Extent of coastal flooding and erosion under one scenario of sea-level rise in the San Leandro area of northern California. Produced by the Pacific Institute, California Energy Commission, California Department of Transportation, and the Ocean Protection Council.
Extent of coastal flooding and erosion under one scenario of sea-level rise in the San Leandro area of northern California. Produced by the Pacific Institute, California Energy Commission, California Department of Transportation, and the Ocean Protection Council.
How will climate change affect where you live? Well, if you’re a Californian, then a new report out this week — from the California Natural Resources Agency and others — spells out just how the Golden State and its residents will need to adapt to climate change in the 21st century.

With the release of a consultation draft of the "2009 California Climate Adaptation Strategy," California has become the first state in the United States to develop a comprehensive plan aimed at adapting to climate change. Until now, most of the emphasis has been on mitigating climate change — reducing greenhouse gas emissions to avoid unmanageable conditions in the future. But policymakers have realized that adapting to the inescapable climate change that is already happening statewide, and that will continue in the decades to come, is the other equally-important side of the coin.

Over the last century, sea levels have risen by up to 7 inches along some parts of the California coast. Average temperatures are higher, there are more frequent, intense forest fires and the water cycle is changing, with less snow falling in winter. Growing seasons are growing — in length, that is. And the state’s already-overstretched water supply is projected to shrink under even the most conservative climate change scenarios.

So what to do? The report’s recommendations include:

  • Reduce per-capita water use by 20 percent by 2020 (this will also bring energy savings, since about one fifth of California's energy demand comes from moving water around the state);
  • Avoid new development in areas prone to flooding, sea level rise, temperature and precipitation changes;
  • Firefighters should incorporate climate change impacts into their planning;
  • Ensure that by 2020, one third of the state's energy supply comes from renewable sources, and in ways that protect sensitive habitat;
  • Identify and protect aquatic habitats and species that could become extinct as a result of climate change.
All the while, the report says, climate change research should be funded, expanded and fed through to policymakers and California agencies. A recently-forged partnership between NASA's Jet Propulsion Laboratory, the California Institute of Technology, the City of Los Angeles and the Los Angeles Department of Water and Power, aimed at improving energy efficiency and saving water, is one example of the sort of symbiosis the state is looking for.