Global climate change: predicting the weather.

In Greek mythology, Prometheus stole fire from the gods and gave it to humans. His action infuriated Zeus, who then chained the giant to a rock in the ocean where he was lashed by the seas and burned by the sun. Today, humans' ability to capture energy and use it as we wish may be leading us toward a similar fate. Records from glacial ice cores and direct air sampling confirm that since the industrial revolution, atmospheric concentrations of numerous greenhouse gasesthose that allow sunlight energy in the earth's atmosphere, but prevent heat from escaping-have increased substantially. Records also indicate that global mean temperatures have risen during this time, with a corresponding rise in sea level. Many climatologists believe that most of the increase in greenhouse gases is due to human activities such as deforestation and the burning of fossil fuels. Their best estimate is that if we continue these activities at present rates, temperatures will continue to rise by about 0.30C each decade. Questions abound concerning climate change, such as whether increased concentrations of greenhouse gases definitely cause global warming or whether the warming is a normal climate variation; how the climate will change in the future, and what the impacts on human health, agricultural production, and natural ecosystems will be; and whether people have enough confidence in the predictions to justify legislating, or at least encouraging, changes in lifestyle such as building more energy-efficient homes or switching from coal-fired power plants to nuclear power. Climate is the result of complex interactions of a vast number of processes. It is impossible to replicate climate in a laboratory and detailed historical records are limited. The difficulty of trying to forecast even local climate more than a few days in advance is summed up by the adage "it's like trying to predict the weather." Forecasting local weather presents a chalSuki Manabe lenge to the best meteoroloissues of c gists, and trying to predict must be appi global climate over decades or modeling. centuries is a formidable task. By analyzing ice cores sampled from Greenland and Antarctica, scientists have been able to see how atmospheric levels of greenhouse gases differed in the past, and they can compare those differences to known variations in global temperature. But to predict how a build-up of greenhouse gases may affect climate in the future, scientists must rely on mathetical modeling. Climate modeling has been conducted since the mid-1950s, when the rise of com-