Climate Catastrophe? Here's What the U.S. Could Look Like in 2100

Southwest: Arizona, New Mexico, California and Nevada

What we could see in 2100: Drought and water shortages, heat waves and wildfire

The Southwestern states, which in the global warming equation include California and Nevada, will experience intense heat waves, poorer air quality, wildfire, water shortages, drought and expanding risks to agriculture. "In general, the main worry in the Southwest is water resources," says Trenberth. "The area is already semi-arid. Water is already a scarce resource what with increasing population demands. These areas are already quite dependent on water flowing from the mountains, so any changes in snow pack ultimately affects the flows in the Colorado River basin and water sources in places like California."

Dry conditions and high temperatures will increase risk for heat waves and wildfires, says Trenberth. "Along with that come issues with insects and diseases. Some insects, such as the Pine Bark Beetle, flourish with a longer summer season, and the dead trees they create lead to higher wildfire risk.

And then there are the water issues. "The increased heating of the earth's surface not only raises temperatures, but it increases evaporation which makes dry soils even drier," says Hurrell. "Droughts will become more severe, frequent and longer lasting."

"We're already seeing the impacts of climate change on public health," says Knowlton. "Heat waves are just one example. They send thousands of extra people to emergency rooms and hospitals, as our study of the 2006 California heat wave showed." Knowlton says that during that particular episode more than 16,000 excess emergency room visits and 1,200 additional hospitalizations happened in a 2-week period, costing the state of California $133 million.

California will also see a two- to three-foot rise in sea level, while San Francisco will see slightly more than that.

Jean Weiss is a regular contributor to MSN Green.