One of the challenges of understanding weather and climate change in the U.S. involves a simple fact: this country is really big. Huge—and that means there’s almost always significant variety in the weather from sea to shining sea. A heat wave in one part of the country might be matched by unusually cool weather in another part. There might be droughts even as there are floods a couple thousand miles away. Compare that to countries like Britain and France, which are compact enough to experience any extreme weather events all at once. Maybe it shouldn’t be surprising that Americans are split on climate change: we can’t even agree on the weather.
The wild weather of this past spring, which thankfully ends in just a few days, might be the perfect example. According to Jeff Masters of the meteorology website Weather Underground, nearly half the country experienced either abnormally wet or abnormally dry conditions—the highest percentage ever seen on record. And for much of the country, when the rain came it came in droves—the percent area of the U.S. featuring much-above average precipitation for one day was 16% a new record. That led to historic floods along the Mississippi and Missouri rivers which are just now beginning to crest. In Mississippi alone 900,000 acres of farmland were flooded—10% of the total acreage in the state—and 6.8 million acres of land were flooded throughout the entire Lower Mississippi Valley. And all that excess water—and fertilizer runoff—will contribute to what could be a record-sized dead zone in the Gulf of Mexico later this year.
This graph from the National Oceanic and Atmospheric Administration (NOAA) gives you a sense of just how unusual the spring of 2011 was:
And that’s just the rain. The spring of 2011 will most likely be remembered for one of the deadliest and most damaging tornado seasons on record. Jason Samenow of the Washington Post lays down just how out of the ordinary this spring’s cyclones were:
* Most active April on record with 875 tornadoes (average number past decade: 161)
* Preliminary: Most January-May tornadoes on record (since 1950)
* 314 deaths from April 27 tornado outbreak, fourth most on record in a single day
* 151 deaths from Joplin, Mo. tornado on May 22, seventh most deaths from a single tornado on record
* Through June 7, 525 tornado deaths – sixth most on record in a single year.
While the Southeast weathered tornadoes and the great rivers flooded, Texas and much of the Southwest went bone dry. This spring was the driest on record in Texas—not a state known for its plentiful rainfall even in a good year—and dry weather has helped fan the flames of wildfires in the Southwest, especially in Arizona, where the Wallow fire is now the state’s biggest ever. “There’s been exceptional drought in Texas and other areas,” said Tom Karl, the director of the National Climatic Data Center. “How long it will persist remains to be seen.”
All of this extreme weather has added up. Natural disasters this year have cost the U.S. more than $30 billion so far—and we haven’t even entered hurricane season yet. (And that season is predicted to be worse than normal.) Damages and even death tolls aren’t necessarily the most reliable measure for how severe weather is getting—after all, as we get more populous and richer, we have more property in the way of tornadoes, floods and wildfires. And as unusually high as the death toll from this spring’s tornadoes was, on a per capita basis the number of Americans killed by cyclones has generally declined over the past 85 years or so. “2011 was well above anything we’ve seen in the recent record, but at the same time, 2011 would have seemed like an average year before 1925,” said Harold Brooks, a researcher for NOAA. “A year we think of as being unusually full of disasters would have been like an average year for my grandparents.”
Nonetheless, by any standard the weather these past few months has been totally crazy. The next question, of course, is what role climate change might play. Short answer: definitely something. While tornadoes in particular are difficult to pin on warming, extreme rain is likely climate related. “It’s hard to single out events like this spring,” says Karl. “What we do see is the extremes of precipitation are generally increasing as the planet warms and more water evaporates from the oceans. Extreme rain and extreme snow can become more intense than they would have been without the climate effect.” In other words, the wild ride may just be beginning.
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