Probing Question: How hot will Pennsylvania be in 100 years?

Those who have spent a winter in State College might have trouble buying into this whole global warming thing. Climate scientists at Penn State, however, maintain that even frigid central-Pennsylvania winters will be influenced by predicted increases in the so-called greenhouse effect. Using global and regional-scale climate models, these scientists are trying to pinpoint the regional effects of this global phenomenon.

Climate models work by simulating Earth's response to increased levels of greenhouse gases, says Eric Barron, distinguished professor of geosciences and dean of the College of Earth and Mineral Sciences. Much of the incoming energy from the sun passes through the atmosphere and heats the surface of the Earth. Greenhouse gases, principally carbon dioxide and methane, selectively absorb heat that is radiating spaceward from the surface, thus creating warming. Climate models reproduce these atmospheric conditions, while factoring in climatic impacts of oceans, continents, and vegetation, to offer the best picture of what the future may hold.

temperature difference graph
Mid-Atlantic Regional Assessment

Projected increases in maximum temperature and precipitation in the Mid-Atlantic region according to two leading global climate models, one developed by the Canadian Centre for Climate Modeling and Analysis, the other by the Hadley Centre for Climate Prediction and Research.

The problem is, says Barron, that picture varies considerably. Even our best supercomputers have trouble incorporating the complex interactive physics that govern our planet. Although Barron maintains that scientists no longer debate whether the Earth is warming, there remains the question of just how much. Today's best global models, of which there are more than 30 worldwide, offer a wide range of predictions.

Regional impacts are even harder to predict. "The reason is simple," Barron says. "In order to get a specific place right, we have to simulate all the details of the atmosphere and even of the land surface. This is a challenge for modern computers and for our understanding of complex features in the atmosphere." Though current local models are uncertain, he notes, they are both necessary and rapidly improving.

Brent Yarnal, director of the Center for Integrated Regional Assessment, works to promote research and education on the local and regional dimensions of environmental change issues, such as climate change. He has worked on a project called the Mid Atlantic Regional Assessment, or MARA, one of 19 regional assessments conducted under the U.S. National Assessment in cooperation with the U.S. Global Change Research Program. MARA, which lasted three years and ended in 2000, analyzed the effects of climate variability and change on the area including New York, New Jersey, Maryland and Pennsylvania. One of the project's primary aims was to predict how climate-related changes in agriculture, water, and forest cover will impact our health and the way we live.

In the worst-case scenario, Yarnal says, climate scientists predict the mid-Atlantic region heating up by about ten degrees Fahrenheit by 2100, with no change in precipitation. A ten-degree average increase in temperature, he notes, would have very serious consequences. Warmer temperatures could increase pathogen development and survival, facilitating disease transmission. Weather variability caused by warming could severely disrupt natural ecosystems and even push certain species to extinction. In addition, Yarnal states that "things would be much drier because the greater heat would result in more evaporation, so less water available for use." "Forget snow skiing and ice-skating," adds Barron. "In this model, it is rare for any precipitation to fall as snow."

The other plausible model, Yarnal reports, "is a much milder, wetter model that gave us a more moderate scenario of future climate." This prediction has us heating up by "only" four degrees Fahrenheit by 2100, with a considerable rise in precipitation that could compensate for increased evaporation. But even this level of change, notes Yarnal, would be enough to bring significant consequences. Studies suggest that any rise in average temperature could upset normal weather patterns, increasing both the frequency and intensity of droughts, floods, and hurricanes.

Although it will take years to narrow the range of predictions offered by climate models, Barron warns against a passive attitude about potential consequences. "Even the models that are relatively insensitive to increased levels of carbon dioxide produce a large warming," he says. Projects like MARA, which take a pro-active approach to understanding regional impacts, are vital for effective planning and policy-making for the future. "By assessing vulnerabilities," says Barron, "we may be able to determine the extent to which human and natural systems can adapt or the extent to which humans may wish to mitigate the warming."

Eric Barron, Ph.D., is a distinguished professor of geosciences, and Dean of the College of Earth and Mineral Sciences. He can be reached at Brent Yarnal, Ph.D., is a professor of geography, and was co-principal investigator for the Mid-Atlantic Regional Assessment. He can be reached at

Last Updated February 01, 2005