May marks month of global weather extremes
WASHINGTON – Even for a world getting used to wild weather, May seems stuck on strange.
Torrential downpours in Texas have whiplashed the region from drought to flooding. A heat wave has killed more than 1,800 people in India. Record 91-degree readings were recorded in Alaska, of all places. A pair of top-of-the-scale typhoons shook the Northwest Pacific. And a drought is taking hold in the East.
“Mother Nature keeps throwing us crazy stuff,” Rutgers University climate scientist Jennifer Francis said. “It’s just been one thing after another.”
Jerry Meehl, an extreme-weather expert at the National Center for Atmospheric Research, points out that May is usually a pretty extreme month, with lots of tornadoes and downpours. Even so, he said, this has been “kind of unusually intense.”
Francis, Meehl and other meteorologists said the jet stream is in a rut, not moving nasty weather along. The high-speed, constantly shifting river of air 30,000 feet above Earth normally guides storms around the globe, but sometimes splits and comes back together somewhere else.
A stuck jet stream, with a bit of a split, explains the extremes in Texas, India, Alaska and the U.S. East, but not the typhoons, Francis said.
Other possible factors contributing to May’s wild weather: the periodic warming of the central Pacific known as El Nino, climate change and natural variability, scientists say.
Texas this month has received a record statewide average of 8 inches of rain and counting. Some parts of the Lone Star State and Oklahoma have gotten more than a foot and a half since May 1. The two states have gone from exceptional drought to flooding in just four weeks.
Texas state climatologist John Nielsen-Gammon attributes the heavy rainfall to an unusually southern fork in the jet stream, a stuck stationary front and El Nino, and said the downpours have probably been made slightly worse by climate change.
For every degree Celsius the air is warmer, it can hold 7 percent more moisture. That, Nielsen-Gammon said, “is supplying more juice to the event.”
While it is too early to connect one single event to man-made warming, scientific literature shows “that when it rains hard, it rains harder than it did 20 to 30 years ago,” said University of Georgia meteorology professor Marshall Shepherd.
The heat wave in India is the world’s fifth-deadliest since 1900, with reports of the 100-degree-plus heat even buckling roads. And it’s a consequence of the stuck jet stream, according to Francis and Weather Underground meteorology director Jeff Masters.
In the United States, New York and other major Northeast cities are flirting with setting monthly records for drought, he said.
El Nino is known to change the weather worldwide, often making it more extreme. This El Nino was long predicted, but came later and weaker than expected. So experts dialed back their forecasts. Then El Nino got stronger quickly.
Some scientists have theorized that the jet stream has been changing in recent years because of shrinking Arctic sea ice, an idea that has not totally been accepted but is gaining ground, Shepherd said.