Research scientists and others studying the Earth’s climate say global warming could be linked to a signature weather pattern seen around the world that possibly contributed to this year’s drought and the ferocity of Hurricane Sandy.
Some evidence indicates climate changes are pulling jet stream air flows into a more north-to-south pattern rather than west-to-east, intensifying atmospheric blocking from the high pressure zones that are created. The zones block weather in place for a longer period.
The implications are powerful: An increase in blocking patterns could in turn increase the frequency of extreme weather.
Blocking air flows for lengthy periods lets wet weather soak some parts of the nation while dry areas stay dry from lack of rainfall. A high pressure zone was present during the unusually warm March this year.
All 88 counties in Ohio qualified for federal emergency drought programs after the hot summer. It’s the worst drought period since the Dust Bowl of the 1930s, according to the National Oceanic and Atmospheric Administration’s National Climatic Data Center.
With Sandy, a high-pressure zone near Greenland pushed the storm onto land and also intensified it with cold air. Without the block, it would have gone out to sea.
The same blocking pattern was noted in the 2010 Russian heat wave and simultaneous massive Pakistan floods, both of which killed thousands. The flooding covered at least 14,390 square miles between July 28 and Sept. 16, 2010. The Russian heat wave and wildfires occurred 1,500 miles away. A blocking system is also linked to Europe’s killer 2003 heat wave, blamed for tens of thousands of deaths.
Much research is still needed. Ryan Fogt, Ohio University assistant professor of meteorology, said no one can say how often over a long time period such blocks will form or where. “The jury is still out,” he said. “We don’t have the predictive capacity over decades or centuries.”
Fogt said the blocking high pressure zones occur naturally, but global warming might influence their position or intensity. “I would say we still have a lot to learn yet about how they will evolve in a warming world,” he said.
The patterns might coincide with ocean temperatures, which affect the jet stream.
A study by the National Center for Atmospheric Research led by Kevin Trenberth and published in September by the Journal of Geophysical Research noted a blocking pattern that accompanied the Russian heat wave and Pakistan floods.
Trenberth, in an e-mail exchange, said ocean temperatures far from the Russian heat wave “played a major role in the intensity and persistence of the blocking.”
He added that science has not concluded with certainty that blocking high pressure zones are a sign of global warming.
“I think that has a ways to go,” Trenberth said. “There is an association, but it is not clearly cause and effect. I think it may be that the waves in the jet stream, etc., may help (increase) the high Arctic temperatures. The mechanism of how it works is not clear and it has not been replicated in models.”
An earlier paper by NASA scientists published in 2011 also linked the single blocking pattern to the Russian fires and Pakistan floods.
“Both events attained maximum strength at approximately the same time,” NASA said. “The researchers found by analyzing satellite data generated by NASA instruments capable of measuring the land surface temperature, precipitation intensity and wildfire activity.”
In a research paper published in October in Geophysical Research Letters, a team led by James Overland of NOAA’s Pacific Marine Environmental Laboratory in Seattle, Wash., examined subarctic wind patterns in the early summer between 2007 and 2012 as compared to the average for 1981 to 2010.
They discovered that the previously normal west-to-east flowing upper-level winds have been replaced by a more north-south undulating, or wave-like pattern. This new wind pattern transports warmer air into the Arctic and pushes Arctic air farther south.
“Our research reveals a change in the summer Arctic wind pattern over the past six years. This shift demonstrates a physical connection between reduced Arctic sea ice in the summer, loss of Greenland ice, and potentially, weather in North American and Europe,” Overland, a NOAA research oceanographer, said.
WHIO-TV chief meteorologist Jamie Simpson said the north-south pattern of atmospheric air flows create the blocking patterns because pockets of air break off and establish as high pressure blocking zones.
The NOAA researchers said that with more solar energy going into the Arctic Ocean because of the lost ice, there is reason to expect more extreme weather events - heavy snowfall, heat waves, and flooding in North America and Europe. They’ll vary in location, intensity, and time.
“What we’re seeing is stark evidence that the gradual temperature increase is not the important story related to climate change; it’s the rapid regional changes and increased frequency of extreme weather that global warming is causing,” Jennifer Francis of Rutgers University said with the paper’s release. “As the Arctic warms at twice the global rate, we expect an increased probability of extreme weather events across the temperate latitudes of the northern hemisphere, where billions of people live.”
National Center for Atmospheric Research senior scientist Jerry Meehl said the study of blocking patterns has long been of interest because they have such a major impact, including during the 1930s Dust Bowl.
“The trick is when a block forms or goes away,” he said. “It’s difficult to predict. To a large extent, blocking is a tough nut to crack.”
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