Long-term forecasting uses mathematical models that consider carbon dioxide, circulation patterns around the globe, and much more. In the end, different models produce various predictions. Still, scientists can point only to a range of possibilities. An upcoming report from the National Assessment Synthesis Team predicts that temperatures could increase, on average, between 5 and 10 degrees. Some areas might get hotter than others, but major swings in peak temperatures are unlikely.
Cities already experience significant warming.
A city's summer temperature can soar 6 to 8 degrees above surrounding regions. These urban heat islands arise because buildings and pavement absorb so much heat. Moreover, fewer trees in cities reduce shading and evapotranspiration, in which plants use up heat by, essentially, sweating. As carbon dioxide builds up, precipitation patterns also will change. Most models predict rainfall increases of 5 to 20 percent.