Some areas experienced historic floods, others saw historic droughts. Is climate change to blame?


Natural Resources Defense Council

A once-in-five-hundred-year flood inundated the Mississippi River valley. A once-in-a-century drought in Texas shriveled the summer's crops and sparked sweeping forest fires. The deadliest tornado season on record tore communities to splinters. 2011 was clearly a year of extreme weather. 

Perhaps it is a sign of the pending 2012 apocalypse, but more likely, it is the result of a changing climate that is amplifying extremes. The chart above marks more than 2,900 separate weather records broken this year, and these records were costly. In all, Mother Nature inflicted $52 billion dollars in damage on the United States.

However, 2011 is not the most expensive natural disaster year on record. That distinction belongs to 2005, the year Hurricanes Katrina and Rita caused more than $150 billion in destruction along the Gulf Coast. The difference is that 2005 had only five disasters that reached the billion dollar mark; 2011 had 12, and according to the National Oceanic and Atmospheric Administration, that sets a new record. 


Two of the most consequential weather stories of the year were the drought in Texas and the tornado season in the Midwest. For most of the spring, summer, and fall, the Lone Star state was plagued by exceptional drought -- the highest level recorded by the U.S. drought monitor. The situation has eased somewhat in recent weeks, but climatologists say that because of the persistent pattern of La Niña (cooling off the coast of South America influencing the jet stream over North America), the drought is likely to linger into the new year. 

The impacts of the record-breaking summer were enormous. Texas reservoirs sank to their lowest levels in years, even revealing long-forgotten underwater ghost towns. Authorities began predicting long-term water shortages in the state. Crops withered. Cattle herds died in the sun, causing the price of beef and other staples to increase across the country. Nearly half a billion trees perished for lack of rain. On this map comparing average temperature and average rainfall for Texas summers, it is not difficult to find the outlier.
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And of course, some of the most powerful images of nature's destruction this year came from Joplin, Missouri, where an EF-5 tornado killed 159 people and destroyed 700 homes. But this was only one of several deadly tornado outbreaks in 2011. In total, 552 Americans died in twisters this year, 12 times the number of tornado deaths of last year and the most since the 1950s. 



While it is hard to blame all of this meteorological activity on global warming, 2011 provides evidence of a planet with a wilder climate.

"This year we had three weather events that matched or exceeded three U.S. weather extremes,"  Jeff Masters, a meteorologist and founder of The Weather Underground blog, says. The Mississippi flood was higher than any other, the Texas drought was drier than any other, and the tornado season was deadlier than any other. "It boggles my mind." 

Additionally, Masters finds the records broken this year to be indicative of a more extreme planet. "Fifty-six percent of the U.S. had a top 10 percent wettest or driest year. That's a record." That divergent pattern is to be expected with climate change -- the wet areas will grow wetter, the dry areas drier. 

These billion dollar disasters are only likely to increase in the coming years, Masters says, and  population growth and increasing wealth factor in as well. If there are more structures to destroy, one storm will cause increasing amounts of damage.

"The climate has changed," Kevin Trenberth, Distinguished Senior Scientist at the National Center for Atmospheric Research, tells me via email. He says since the 1970s, the water vapor over the oceans has increased by 4 percent. That water vapor acts as fuel to weather systems, contributing to the severity of the Mississippi flood, and to the thunderstorms which produced the spring's tornadoes.

"Hurricane Irene flooding had a component (5 to 10 percent) from human-induced global warming," he says. "It may not sound like much but it is often the straw that breaks the camel's back." 

Here's a recap of the some of the top weather disasters in 2011. (This list is limited to the U.S. The rest of the world had its own share of nature-inflicted tragedy this year, including the 9.0 Japanese earthquake that killed 10,000 people and cost $309 billion.)

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