Report gives sobering view of warming's impact on US

So far, the region's population growth has come during a relatively wet period; but that is already changing, with reduced snowpack in the mountains and significant die-offs in pinon pine populations in the Four Corners area. Periodic droughts are nothing new here, but the current one is being made worse as higher temperatures force already-scarce water to evaporate from the ground more quickly.

Taken together, these factors make water a very scarce and precious resource, one that will come under increasing pressure as springtime precipitation is projected to decrease, while average temperatures are likely to shoot up by 7 to 10 degrees F. Longer, more severe droughts are pretty much inevitable under any emissions scenario, and under the high-emissions scenario they could be devastating. Scarce water resources would presumably go to people first, leaving California's economically vital agricultural economy difficult to sustain. The inevitable drawdown of giant reservoirs such as Lake Mead will also reduce the reliability of hydroelectric power. 

NORTHWEST

The temperature rise in the Northwest has been smaller overall than in other parts of the nation - roughly 1.5 degrees F over the last century. The effects are clear nevertheless, particularly in the decline of spring snowpack, which means less water flowing into surrounding aquifers and irrigation systems in summer. The drop in snowpack and runoff could also mean a reduction in hydroelectric power, which provides 70 percent of the region's electricity needs. And as more winter precipitation falls as rain and snowmelt begins and ends earlier, streams will run faster in spring, damaging spawning areas salmon depend on, and then run warmer in summer, threatening the fish themselves, which die when the water temperature is too high.

Pest infestations due to warmer winters are already having a devastating effect on western pine forests, where pine beetles have destroyed 2.5 million acres of Rocky Mountain woodlands. Such infestations will likely become more widespread, creating tinder for forest fires that will intensify during warmer, drier summers.