From the perspective of their individual specialties, Cornell's earth and atmospheric scientists weigh in on climate change and global warming.

At multiplexes all over the country, Tokyo is being pummeled with hailstones the size of fists, Delhi is covered in snow, and New York City is facing a new ice age, the temperature falling at a rate of ten degrees per second. It's all part of The Day After Tomorrow, Hollywood's doomsday version of global warming, wreaking havoc on even the wildest scientific predictions.

Back in the real world, Arthur DeGaetano, in his office at the Northeast Regional Climate Center (NRCC) on the Cornell campus, talks calmly about the weather and the statistical realities of climate change. After decades of debate between scientists who saw global warming as the end of the world and others who saw it as nothing but hot air, DeGaetano places himself in the middle of the spectrum, convinced of the reality of climate change but unconvinced of any immediate danger for most of the world.

"There are still skeptics in the field, but in the last few years, I've seen them change their views on global warming," says DeGaetano, associate professor in the Department of Earth and Atmospheric Sciences (EAS) and director of the NRCC. "At this point, the evidence for climate change is just too compelling, and anyone who wants to argue that it ’s not happening is just fooling themselves."

With his colleagues in EAS, he's moved the discussion beyond theories of global warming and into the world itself. Instead of creating models to predict the long-range effects of global warming, Cornell scientists are studying the impacts of climate change all around us and investigating the physics underneath those changes. Charles Greene and Andrew Pershing study changes in the North Atlantic Oscillation, using an index that measures the difference in atmospheric pressure between Iceland and the Azores, and its impact on endangered right whales feeding off the coast of North America.

Kerry Cook uses computer models to study physical interactions at the interface of earth, ocean, and atmosphere to better understand the mechanics of climate change and variability. Applications include African drought, mountain glacier retreat, and the stability of the climate that supports the Amazon rainforest. Susan Riha studies how land use change, such as deforestation in the Brazilian frontier, alters the transfer of water and chemicals between the land and the atmosphere, which can influence climate.

"The idea of having a Department of Earth and Atmospheric Sciences is to emphasize the interactions between the spheres — the lithosphere, the biosphere, the hydrosphere, and the atmosphere — that in the past have been studied more or less in isolation from each other," says Riha, until recently the associate department chair in EAS. "We're interested in identifying the drivers of climate change. We're interested in understanding how climate change impacts systems. We're interested in knowing how people can respond to the impacts of climate and climate variability. What ties our work together is an interest in understanding how each of these parts affects the others."

Focusing on the last hundred years of weather in the United States, DeGaetano sees a few clear trends in climate change. Since the beginning of the 1900s, when scientists started keeping data, temperatures have risen, plateaued, and risen again. Though DeGaetano's work doesn't try to pin-point the origins of the changes, that first rise, from 1900 to about 1940, was probably due to natural causes like solar variability and volcanic eruptions; the second rise, starting around 1970 and continuing steadily into the present, is probably man-made, resulting from the growing effects of greenhouse gases in the atmosphere, largely from the increased use of fossil fuels.

Over the same hundred years, the amount of precipitation has stayed fairly constant as its distribution has become increasingly uneven, with longer rainfalls and longer droughts.

DeGaetano's work focuses on extreme events, and its basic applications are in building design, where it can be used to model snow loads on roofs and frost depths for foundations. As for the larger question, DeGaetano is still open for debate: Are changes in atmospheric circulation influencing changes in temperature, or is it the other way around? "It's not only that temperatures are getting warmer; the atmosphere is behaving in a different manner," says DeGaetano. "And the more you study climate change,the more difficult it is to see any one piece. You really have to look at the whole system."

For Kerry Cook, the key to predicting how climate may change in the future comes from understanding the physical mechanisms that underlie those changes. "When I started teaching climate dynamics 12 years ago, the warming signal was less pronounced and I expressed a level of scientific skepticism to my students," says Cook, professor in the Atmospheric Science and Science of Earth Systems programs, two of three undergraduate majors offered by EAS. "Now, however, with the increased and consistent warming of the last decade, there is negligible uncertainty that human-induced global warming is a reality,and it is past time for humanity to react."

"One way of learning about climate change and of building confidence in our ability to predict it," Cook says, "is to apply the same models used to predict future climate to climates of the past. For example, the Sahara Desert was green from 5,500 to 14,500 years ago and dotted with large lakes. And 21,000 years ago, the Amazon basin was significantly drier than today." Cook and her research group have been able to capture these climate change signals in computer models, and they are analyzing the information to understand how observed past climate states were established and how future climate change scenarios may play out. Of special interest is an evaluation of climate system nonlinearities, such as those associated with interactions between land surface and atmospheric processes,which can lead to threshold behavior. When a threshold is reached, the climate system can change rapidly, making adaptation very difficult for human and natural systems.

Another way of building a physical understanding of future climate, Cook says, is to study the variability of today's climate. She and EAS postdoctoral associate Ned Vizy have studied how warming in the Gulf of Guinea forces drying across the African Sahel through the regulation of surface moisture fluxes into the West African monsoon. Along with graduate students Jen-Shan Hsieh and Samson Hagos, she has found that summer warming over southern Africa causes drying over northeastern Brazil. Cook and undergraduate researcher Christina Patricola have cataloged the characteristics of African easterly waves, which are shed off the west coast of Africa into the tropical Atlantic in summer and initialize hurricane formation.

On Georges Bank and in the Gulf of Maine, where they were analyzing year-to-year variability in zooplankton populations, Charles Greene and Andrew Pershing happened onto one of the most significant climate changes in the last hundred years. Their 1997 data was exactly as they'd expected, but when they returned a year later, their results were unlike anything they'd ever seen in the literature.

"We knew something big was going on, but we didn't really know what," says Greene, professor in EAS and director of Cornell's Ocean Resources and Ecosystems Program. "In fact, two years earlier we had seen the strongest drop in the North Atlantic Oscillation index during the 20th century, and we were able to show that the NAO can have really dramatic influences on the physical and biological oceanography off the Northeastern United States.

 "That's been our contribution so far to climate change research," continues Greene. "By understanding how climate processes in the atmosphere affect other processes in the ocean, we now have the knowledge base to begin making predictions about how ecosysytems will change in the future, not just due to natural climate variability, but also to anthropogenic climate change."

"We can now observe what the NAO does in a particular year and forecast how it will affect the physical environment in the Gulf of Maine the following year," says Pershing, an assistant professor in EAS with a joint appointment in Computing and Information Science at Cornell. "The holy grail in all of our climate work is whether you can say anything about fisheries. Right now, we feel we can do a pretty good job of predicting whether there's going to be a good or bad year for some zooplankton in the Gulf of Maine. Good years for plankton could produce good years for fish reproduction — with a possible result of good fishing a few years after that."

Pershing has continued work in the Gulf of Maine, designing models to forecast the future behavior of right whales and keeping watch on a new theory that changes in the NAO may actually be determined by events in the Indian Ocean. Meanwhile, Greene has moved on to Hawaii, where he's researching the effects of climate variability on marine life in the Pacific Ocean.

At the Kohala Center in Hawaii where EAS has established a field program, Greene is creating the Hawaiian Ocean Resources and Ecosystems Observatory (HI-OREO) and the Hawaiian Underground Listening Array (HULA) to track fish, marine mammals, and sea turtles from the coast of the Big Island to the point where the ocean becomes 1,000 meters deep. "It's a tremendous volume of ocean, a scale that biological oceanographers have never tried to observe before," says Greene. "Our goal is to get continuous, three- dimensional, high-resolution positions of animals to track them, and once we're able to do that, then we'll be able to see how animals react to both natural and man-made changes in their environment. We'll be able to study their behavior as the ocean changes."

In the Brazilian rainforest, where large-scale deforestation has had a major impact on carbon production and the hydrologic cycle, Riha focuses on the interaction of soils, plants, and the atmosphere. Studying the effects of deforestation on radiation interception and evapotranspiration, she laid the groundwork for applied problems in plant productivity. Her group has found that although secondary forests can experience rapid early growth, they quickly plateau, fixing less carbon than primary forests.

"There is a lot that we don't understand about climate dynamics in a major region like the Amazon," says Riha, "and a lot still to be understood about how land use affects climate and carbon dioxide in the atmosphere. I'm the kind of person who gets out there to see what's actually changing at the surface,and brings the data back to people like Kerry, who are building the models. That's what all this comes down to — the surface exchange of water and energy,and how that can affect your climate."  

Like Cook, Riha is concerned about triggers that can cause rapid climate change; and like DeGaetano,who's heard too many questions about this past January's cold spell — "If you look at the lows this winter," he says, "it's really not unprecedented"— Riha faces the task of teaching the non-scientists around her about the constant, ongoing process of climate change.

"Most people think of climate as remaining fairly stable, so it's the challenge to get people to see that climate is dynamic," says Riha. "Clearly, we can see that here in Ithaca, because just 12,000 years ago, there was a half-mile-high sheet of ice where we're sitting right now."

For DeGaetano, looking at the photographs of his children as he talks about the future, the real questions aren't about temperature — they're about water, "which I think is going to be the biggest problem to face society in 50 years." By then, as his children reach retirement age, they will have gotten used to the warmer temperatures, adapting to long-term changes in climate, and coming to accept them as perfectly normal. But with the larger trend toward more droughts and more floods, DeGaetano sees a world of haves and have-nots,of the demand for water outstripping the supply. 

"Groundwater is being depleted and not replenished, and there are already places out West where by the time you get to the end of the river, there's very little water left to draw," says DeGaetano. "It creates problems, because to avoid flooding you don't want to have a reservoir full of water. And to avoid a drought, you want to make sure your reservoir has enough water to meet all your needs. So globally, water is going to be a huge issue."

For DeGaetano,as well as for the rest of the department, the answers are as simple to understand as they are difficult to implement: We need to decrease our reliance on fossil fuels, cut back on emissions of greenhouse gases, and prepare to adapt to the changes around us. "The increases in temperature and the changes in rainfall are going to continue," says DeGaetano. "In the short-term, we'll learn to adapt to changes in the weather, because it's a gradual process, and we tend to adjust to it in our thinking. But in the systems that we build, that we've designed for a certain set of conditions, there may not be as much room for adaptation, and we may see the same kind of reactions that we see in the natural world.

"Even if there's a breakthrough tonight in fuel cell technology, and we shut off all carbon dioxide emissions tomorrow, there's still going to be global warming," says DeGaetano. "The climate can't just react in a moment — it has a memory."

Which is, in a sense,reassuring, suggesting that the sudden climate change scenario in "The Day After Tomorrow" is unlikely. But it also lends urgency to the real message: if we want to make a difference in the future, we have to act now.

Kenny Berkowitz ’81 is a freelance writer in Ithaca.