But when scientists built the first statistical models to calculate the effects of rising carbon dioxide concentrations, the models predicted warming trends that were much too high and clearly in error. In the past several years, the model-makers have refined their work. For one thing, they have noted that there are many other compounds that humanity also throws into the air and one class of them, tiny particles of sulfate, reflects solar radiation and offsets the warming trend especially in industrial regions. When the models took that into account, the results began to look more like the data that scientists were actually collecting from their instruments. While the models are improving, some scientists fear that they may be misleading in another respect.
Models usually predict steady, gradual change.
But complex natural systems sometimes contain sudden surprises that, for reasons visible only in hindsight, can speed up change drastically. Those concerns are cited by scientists who warn against excessive confidence in models that are only approximate at best, and based on past experience over a period that is, in geological terms, very short. But in the past five years the models seem to have come significantly closer to describing reality. In the American political style, doubt is interpreted as weakness. When national leaders are pushing for action, they believe that they can't afford to be uncertain.