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| Earth's glaciers are among the parts of our ecosystem most vulnerable to global warming. (Photo by Gary Herbert, NOAA) |
NCAR and UCAR were founded just as the relationship of Earth's residents to their environment was losing its innocence. The Cold War, with its fears of nuclear holocaust, held society in its grip. Pollution episodes in the 1940s and 1950s sickened thousands. At the same time, the progress of technology convinced many that the atmosphere's fury might soon be tamed through weather modification.
None of NCAR's founders foresaw the sweep of events that would put atmospheric science at the center of world affairs. The discovery of an ozone "hole" above Antarctica in the mid-1980s led to a worldwide agreement to restrict its industrial triggers. Global warming—little more than a theoretical concept in 1960—became acknowledged reality by 2000, even as the degree of human responsibility for it remained a topic of debate.
As the nation's only center committed to studying every part of our planet's atmosphere, NCAR has been at the forefront of global change science. Its researchers have teamed with those from universities in traversing the globe, finding telltale signs of human influence thousands of miles from civilization. Its chemists are world leaders in analyzing the makeup of our changing atmosphere and the invisible reactions that drive it. Its climate models have enabled hundreds of university and NCAR scientists to unravel yesterday's conditions and to project today's climate into the future. Through these and other efforts of NCAR and its collaborators, we have learned that our atmosphere is amazingly resistant to tinkering, yet ultimately vulnerable to the byproducts of our everyday lives.
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| Studying the trace gases emitted by tropical plants, NCAR scientists joined others from five nations for an African field project in 1996. (Photo by Lee Klinger, NCAR) |
NCAR began with a relatively sharp focus on several key processes of the global atmosphere: the motion of air, the exchange of energy, the behavior of water vapor. It was years before these disparate topics were linked in a single computer model. NCAR developed one of the first models of global air circulation in the 1960s, but it could depict only a few days of atmospheric behavior, and the data to feed such models were sorely lacking. A 15-year effort (the Global Atmospheric Research Program) helped spur regular observations around the globe by satellite, weather balloon, ship, and buoy. In the 1980s NCAR released its first community climate model (CCM) to the research community. The CCM was initially aimed at simulating the planet's atmosphere for periods of a few months to a few years. Global temperatures had by then begun to climb, after a slight 30-year cooling trend. With the continued addition of carbon dioxide and other greenhouse gases to our atmosphere, the new global models hinted that more warming would likely be on the way.
Blistering heat and crippling drought across the U.S. heartland in 1988 put the spotlight on climate models and made "greenhouse effect" a household phrase. With increased interest and funding, NCAR's climate modeling work expanded quickly. Longer-range simulations covered decades, and finer-scale models explored possible regional impacts such as forest dieback and altered crop yields. Yet even the best models were hobbled by deficiencies, largely due to limits on computer power. The models' depiction of oceans, sea ice, and land surface was simplistic—often these elements were fixed or prescribed, lacking two-way interaction, or "coupling," with the rest of the system. Moreover, the models' climate tended to drift into unrealistically warm regimes.
NCAR soon consolidated its modeling efforts, under the guidance of
Maurice Blackmon, to produce the Climate System Model, released to
universities in 1996 and available freely on the World Wide Web. Now
dubbed the Community Climate System Model (CCSM), this landmark tool
simulates the entire Earth system (atmosphere, ocean, sea ice, and land
surface). The CCSM was the first fully coupled model that showed no
significant "climate drift" without artificial energy corrections. The
model's exhaustive simulation of 21st-century climate showed a potential
warm-up of 2.0° Celsius (3.6° Fahrenheit) by 2100, assuming that
carbon dioxide continues to increase in the atmosphere.
It took years of patient work for the CCSM to accurately reflect the atmosphere's partners in the Earth system: ocean, land, and ice. Ocean modelers Peter Gent (NCAR) and James McWilliams (now at the University of California, Los Angeles) devised a new way to describe the effects of unresolved ocean eddies. The Gent-McWilliams parameterization moves and mixes water properties along surfaces of constant density. This reduces model error and allows a better simulation of ocean temperature and salinity.
Some improvements to the models still await the work of scientists who continue to collect observations and hunt down mechanisms. For instance, only about 60% of the carbon from industrial emissions remains in the atmosphere each year. Some of the rest is accounted for, but much disappears in a yet-to-be-identified carbon "sink." The global rate at which plants absorb carbon dioxide varies dramatically, influenced on a regional scale by volcanoes, wildfires, drought, and even El Niño. NCAR's David Schimel (currently on leave at the Max Planck Institute for Biogeochemistry) and Timothy Kittel are among the leaders of a project examining ecosystem trends across the United States over the 20th and 21st centuries and the resulting impact on carbon storage. Their findings show that the U.S. carbon uptake depends strongly on land use and may vary from year to year even more than previously thought.
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| Flying from Boulder to Hudson Bay and back, the NCAR C-130 traversed North America several times in early 2000 in a field campaign to study the springtime Sun's effect on ozone and other air chemistry. (Photo by James Hannigan, NCAR) |
The survey is only one part of the U.S. National Assessment of the Potential Consequences of Climate Variability and Change for the Nation. Released in 2000, the report outlines the possible regional impacts of climate change and the areas where U.S. society is most vulnerable. As recent as they are, such regional projections would be impossible without years of work at NCAR and elsewhere. Techniques such as downscaling can extract useful information from global climate models on the smaller scales needed. The interdisciplinary aspects of climate assessment range widely: for example, NCAR economist Kathleen Miller has teamed with mathematician Robert McKelvey (University of Montana) and economist Gordon Munro (University of British Columbia) to study the impact of climate variability on Pacific salmon fisheries.
NCAR researchers are among the world's most active in national and international assessments, including two key series on ozone and climate change, both cosponsored by the World Meteorological Organization and the United Nations. Each of the climate change reports prepared by the Intergovernmental Panel on Climate Change (IPCC) involves some 2,500 scientists from across the world. The final reports serve as guidance for governments and other planning bodies. The IPCC's third major assessment is expected in early 2001.
Another element in the mix was El Niño. This periodic warming of
the eastern tropical Pacific first received public attention in
1982–83, but it was the record event of 1997–98 that made El
Niño a household word. Its impacts were predicted months in
advance by the National Oceanic and Atmospheric Administration, and its
progress was tracked by ocean buoys and sophisticated satellites from
NOAA and the National Aeronautics and Space Administration. The period
since 1975, marked by a dramatic global warm-up, has seen twice as many
El Niños as La Niñas (a cooling pattern in the same area).
Trenberth calculated that surface air warms or cools by up to 0.3°C
(0.5°F) during a strong El Niño or La Niña,
respectively. Scientists can extract these influences from analyses of
global climate as they seek underlying trends, such as the amount of
warming that can be ascribed to the greenhouse effect.
Other oceanic cycles, such as the North Atlantic Oscillation and the Pacific Decadal Oscillation, gained attention as the century closed. Even a cycle discovered in the 1970s by Roland Madden and Paul Julian earned new visibility as a possible trigger for El Niño. The Madden-Julian Oscillation—a one- to two-month pulse of storminess moving from west to east across the tropical Pacific—was later found by Eric Maloney and Dennis Hartmann (both of the University of Washington) to strongly affect hurricane activity in the Gulf of Mexico. Meanwhile, governments and societies reaped benefits from improved understanding of teleconnections, or global influences, between these ocean cycles and regional climate patterns. NCAR political scientist Michael Glantz, who began studying El Niño in the 1970s, worked closely with the United Nations Environment Programme to ensure that research results were relevant to policymakers. In 1998, Glantz sponsored the first-ever summit devoted to La Niña.
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| Warren Washington (left) and the late Philip Thompson were two key climate researchers during NCAR's founding days. Thompson, a pioneer in the study of predictability, served as NCAR associate director. Washington, now a senior scientist, created NCAR's first global circulation model with colleague Akira Kasahara. | |
Global change has become the most prominent venue for NCAR's long- standing work in atmospheric chemistry. Much of this work has focused on the stratosphere, the tranquil zone above the "weather layer" of the troposphere. Here, such seemingly innocuous elements as sunlight and clouds can mix with industrial chemicals to wreak havoc. After the ozone hole's discovery in 1985, Susan Solomon (NOAA) and NCAR's Rolando Garcia showed how human-produced chlorofluorocarbons (CFCs) teamed with clouds in the Antarctic's stratosphere to deplete ozone with the return of sunlight each spring. Yet satellites were also detecting ozone depletion in the stratosphere beyond the poles. This smaller but still disturbing and puzzling loss was explained in 1992, shortly after the eruption of Mt. Pinatubo. NCAR's Guy Brasseur (now at the Max Planck Institute) and Claire Granier found that sulfur thrown into the stratosphere by major volcanoes could provide the same ozone-depleting assistance to CFCs as do polar stratospheric clouds. Meanwhile, Michael Coffey and William Mankin found that the chlorine emitted by the same volcanoes played little role in ozone depletion—another piece of evidence that society was the culprit.
The Montreal Protocol was passed in 1987, limiting CFC production worldwide. NCAR scientists stepped up their analysis of CFC substitutes and continued flying to the Arctic and Antarctic to sample polar air. They also joined key international efforts through the 1990s to monitor the global atmosphere on a more regular basis and study its chemical workings in more detail. Sampling atop Mauna Loa in Hawaii and across remote stretches of the Pacific Ocean, they found much larger amounts of pollutants than expected in the relatively pristine air.
One of the most important ingredients in the global climate picture is one of the tiniest: aerosols, the airborne bits of dust, salt, and soot that can serve as nuclei for cloud droplets. A 1999 study based in the Indian Ocean, led by NCAR alumni Paul Crutzen (Max Planck Institute) and Veerabhadran Ramanathan (Scripps Institution of Oceanography), used aircraft and ground-based instruments from NCAR and other institutions to detect aerosols and other evidence of urban air hundreds of miles from India's cities. Aerosols affect climate directly, by reflecting sunlight, and indirectly, by changing the character of cloud cover. As a blend of chemistry and microphysics, aerosol modeling came into its own in the 1990s, with NCAR a center of action. By adding the regional cooling effects of aerosols to global climate models, scientists got a much fuller and more accurate picture of global warming's path. Big questions remain about cloud cover: how much sunlight it reflects, how much radiation from Earth it absorbs, how the types and global extent of clouds are changing. NCAR scientists are part of a major effort, based at Scripps, to examine the links between clouds, chemistry, and climate.
Perhaps the most obvious change in the atmosphere, affecting millions of people in this new century, stems from the global transition from rural to urban life. Megacities, those with ten million or more people, are on the increase. According to the United Nations, the world had 16 megacities in 1996 and 24 in 2000. NCAR launched a program in 1999 using Mexico City as a prototype to study how megacities affect regional climate and air quality. The challenge will be to extrapolate such results to a world of cities growing in wildly different modes that range from suburban sprawl to densely packed urban cores.
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