Computer Models Help Predict the Future
The world is becoming warmer according to thermometers all over the planet, shrinking caps of sea ice, disappearing permafrost and dozens of other indicators. How much warmer will Earth become? Computer models are helping scientists find the answer.
John Walsh with the University of Illinois was in Fairbanks recently to discuss climate predictions. He and other scientists combined the results of nine computer climate models to predict future conditions in the Fairbanks area and the Arctic Ocean.
The computer models predict that during the next 30 years, Fairbanks area temperatures will become 1 to 3 degrees Celsius warmer than they are now. In the next 90 years, area temperatures will rise as much as 8 degrees Celsius. The models foretell warmer winters in Fairbanks, which is consistent with recent scientific studies. The models also show a trend toward cooler summers in the late 21st century. Walsh said increased rainfall would be the cause; the sun is expected to evaporate the added rain, reducing air temperatures.
The results for Arctic Ocean warming show why scientists think the poles are the canaries in the coal mine of climate change. The models show extreme warming—as much as 16 degrees Celsius in autumn and winter—over the next 90 years near the north pole due mainly to the melting of sea ice. Arctic Ocean summers don’t show as much change, due mainly to the ability of open water to absorb heat.
If the model results become reality, Alaskans will be sloshing around in a soup of melted permafrost, most of which is currently within one degree of thawing. Those with oceanfront property throughout the rest of the United States also will have problems—intense warming will cause rising sea levels to flood much of Florida, Louisiana, and other low-lying areas.
What is a computer model, and why do some scientists use them to predict the future? Walsh, an atmospheric scientist, said a computer model is a complex mathematical representation of the forces controlling Earth’s atmosphere, oceans, and land surfaces. Scientists who work on climate models divide the planet into thousands of points. For each of these points, which show up as spots on a map, the computer is set up to work on a series of mathematical equations. For a grid point over the arctic tundra for example, modelers apply Newton’s equation for motion to calculate wind speed; they use other formulas to determine rain or snowfall, evaporation, and dozens of other factors. The supercomputer chews away at these equations, calculating rates of change for each spot on Earth. Then, these calculations are combined to give regional averages of temperature, moisture, atmospheric pressure, and so on. Even with its incredible capacity for calculations, a supercomputer takes weeks or months to simulate just a few decades of Earth’s future climate.
Walsh said computer models vary in their predictions—some call for incredible warming, some for little or none at all. This variation illustrates a problem—models are not yet reliable enough to have punch with policy makers. Walsh thinks models are the best tools available for predicting long-term changes, but he acknowledges they need work. He points out that during the past two decades computer models have doubled the range of accurate weather forecasts, so it may not be long before scientists hone a reliable climate model.
