National Geographic News
Published August 20, 2012
Wondering what's causing all the extreme weather we've seen lately? The short answer, scientists say, is rotten luck and a warmer planet. It's not easy to shatter a record that has lasted for more than 75 years. But that's what happened last month, when a stubborn heat wave pushed July temperatures in the United States into uncharted territory. Not since 1895, when national record keeping began, has the thermometer stayed so high. The average temperature in July was 3.3°F (1.8°C) above the 20th-century average, according to the U.S. National Oceanic and Atmospheric Administration (NOAA), breaking a record set in 1936. Besides making life miserable for people in places like Kansas City, Missouri, where the temperature hit 107°F (42°C) on July 25, the withering heat is also taking a toll on wildlife and crops. Streams in the Midwest got so hot in recent weeks, and water levels dropped so low, that the extreme conditions killed tens of thousands of sturgeon and other fishes. Meanwhile, crops such as corn and soybeans, despite welcome rains across the Midwest this week, have been devastated by the recent drought and are now expected to produce the smallest yields in years, according to the U.S. Department of Agriculture. Warming Supercharging Extreme Weather
The main forces behind these disasters have been natural weather cycles, such as back-to-back La Niñas in 2010 and 2011 that routed storms away from drought-prone parts of North America, and a massive high pressure system, known as a heat ridge, that parked itself over the U.S. this summer and refused to budge. But there's more to the story, said John Nielsen-Gammon, state climatologist in Texas, which just went through the worst one-year drought in its history. It wasn't just bad luck that caused these disasters, he explained. Human-induced global warming was also to blame. (Test your global warming knowledge.)...