Environment
Around the globe, this year’s holiday season is marked by a distinct absence of snow
Record warm ocean surface temperatures in tandem with El Niño in the Pacific Ocean are driving severe weather that is leaving a trail of destruction from the U.S. to Australia, Britain and Latin America, experts said Monday.
El Niño “has allowed more moisture to enter the atmosphere through evaporation,” Bob Henson, a meteorologist and climate blogger for Weather Underground, said. “We’ve had a series of very warm, moist air masses moving up from the tropics. That’s part of what’s fueled the storms and flooding in the South, record warmth in the East and some of the U.K.’s storms.”
El Niño typically lasts for a few months, and “we’re right in the middle of that right now,” he said. El Niño is a periodic warming in sea surface temperatures in the eastern equatorial Pacific. Among its effects are an increase in moist air rising and moving east and north, which contributes to severe rain and flooding in some areas, and record heat in others.
But experts cautioned that El Niño alone doesn’t explain the flooding, tornadoes and other extreme weather around the world.
“We’ve had big El Niños before, [but] we’ve never seen late December heat like this, with temperatures soaring into the 70s in the northeastern U.S.,” said Michael Mann, the director of the Earth System Science Center at Pennsylvania State University.
Each month of 2015 saw record-breaking average temperatures as a result of climate change, though not to the extreme degrees observed in December. But the resulting warmer oceans and moist air moving north from tropical waters helped drive some of the more unusual weather, scientists say.
Together, unusually warm ocean air and El Niño have contributed to recent freakish weather events — severe storms and flooding in the southern half of the U.S. that killed dozens of people over the last several days, floods in parts of Latin America that have displaced more than 100,000 people, the worst floods in 70 years in northern England and unusually high temperatures over the holidays in the northeastern U.S.
Mann said some of the other severe weather in the U.S., including the unusual appearance of tornadoes in the Midwest normally seen in spring, could be attributed to unusually warm moisture-laden air clashing with winter air masses.
“Yes, the randomness of weather is playing a role here. But these events have been supercharged by the extra energy in an atmosphere made warmer and moister by human-caused climate change,” he said.
In the U.S. during strong El Niño years, meteorologists expect to see higher temperatures in the eastern U.S., but not at the level seen this year, Henson said.
“The extremeness of the records surprised everyone,” he said. Normally, record-breaking heat means that the temperatures were a degree or two above the old record. But this year in many places, the temperatures were more than 10 degrees above the old record. “These were certainly amazing records and a sign of how unusually warm and moist this air mass is.”
The above-average temperatures for the northern half of the U.S are predicted to last through March, according to Susan Buchanan, the acting director of public affairs for the National Weather Service.
The same goes for below-normal temperatures for the southern states, she said, adding that there would likely be short-term variability within these long-term trends.
The polar vortex — infamous for bringing Arctic temperatures to much of the continental U.S. in winter 2014 — may bring more cold to the U.S. at the end of January, Buchanan said, but it is currently centered over the Arctic.
“We could certainly get at least one round of more typical winterlike temperatures over the eastern U.S. in January,” Henson said.
Correction: A previous version of this article misspelled Bob Henson's last name.
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