Wildfires in the west, and heat waves and severe windstorms in the east have made early summer, 2012, a devastating time for thousands of Americans.
Conditions leading to the wildfires in the mountains of Utah, Arizona, New Mexico, Montana, and Colorado began with a La Niña winter, a condition that occurs when the sea surface temperature along the equator in the Central Pacific drops by 3 to 5°C (approximately 7 to 10° F). La Niñas historically bring drought conditions to the American Southwest, and the winter of 2012 was no exception. In fact, it was one of the driest on record. The snowpack in the Rockies was only 23% of normal, and the usual spring rains were scarce or nonexistent. Similar conditions existed in most other western mountain ranges. In addition to the lack of precipitation, a beetle infestation had turned millions of trees into deadwood, making western forests tinder dry. With record heat and gusting winds added to the mix, all it took was a lightning strike or a careless camper to start a blaze that roared out of control and eventually destroyed more than 200,000 acres of national forest, burned 1,500 homes, killed 2 people, and caused 30,000 residents to evacuate.
In the east, on June 29, 2012, a derecho windstorm knocked out electrical power to 3 million people. Derechos are straight-line windstorms that can exceed hurricane force, produced by fast-moving bands of thunderstorms that form in hot, humid weather. The derecho winds of June 29 exceeded 100 mph (160kph), snapped power poles, and damaged structures on a 700-mile track from Chicago to the Atlantic coast. At the same time a record heat wave with temperatures exceeding 100° F (37°C) plus high humidity struck the Midwest, the eastern seaboard, and some southeastern states. Without power for air conditioning and refrigeration, there were hundreds of cases of heat exhaustion and at least 15 deaths attributed to the windstorms and excessive heat.
Whether global warming was a factor in these extreme events is not clear, but climate scientists believe they represent a taste of things to come. As world climate warms, heat waves will be hotter and more frequent, and will last longer. Water will be scarcer, and storms of all kinds will pack a bigger wallop.