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article imageStudy finds half of Greenland's warming due to natural causes

By Karen Graham     May 11, 2014 in Environment
The rapid warming of Greenland's glaciers has been documented for a number of years, but atmospheric scientists at the University of Washington estimate that up to half of the warming in Greenland and other areas may be from natural causes.
Greenland and parts of the Canadian Arctic have experienced extreme warming at several times the global average. The temperature increases have been rising about one degree Celsius per decade since 1979.
Qinghua Ding, an atmospheric scientist with the University of Washington, and one of the lead authors of the study published May 7, 2014 in the journal Nature. says, “We need to understand why in the last 30 years global warming is not uniform. Superimposed on this global average warming are some regional features that need to be explained.”
The researchers found that about half the surface warming shrinking Greenland's glaciers is due to temperatures in the tropical Pacific Ocean, and not greenhouse gases. Scientists already know that sea surface temperatures affect global weather patterns in the lower latitudes. "We know that global warming due to human impacts can't explain why it got warm so fast," said Ding.
As an example, the El Niño cycle moves rainfall patterns around the world, bringing precipitation to western North America and causing drought in Australia and Central America. The study used observation and advanced computer models to show how the warmer western tropical Pacific Ocean has caused atmospheric changes over the North Atlantic region.
Ding explained the connection with the tropical Pacific and Greenland comes from atmospheric pulses called Rossby waves. These waves are undulations of high-altitude winds that race around the globe, like the jet stream. Rising warm or cold air over the Pacific Ocean will set off a Rossby wave, and the wave usually favors the warmth over Greenland, according to observations.
Climate conditions and weather events associated with extreme phases of the North Atlantic Oscillati...
Climate conditions and weather events associated with extreme phases of the North Atlantic Oscillation.
Ned Gardiner and David Herring, NOAA
Co-author David Battisti, a UW professor of atmospheric sciences said, “The pattern of the changes in the tropical Pacific that are responsible for remarkable atmospheric circulation changes and warming in Greenland and the Canadian Arctic are consistent with what we would call natural variability.”
The research team says they were not surprised to find the "imprint" of natural variability in a region known for its melting ice. They said that in other areas of the world where warming seems to be happening at an increased rate, global warming and natural variations both contribute to producing a “perfect storm” for warming.
Natural variations in the study focused on an unusually warm western tropical Pacific, near Papua New Guinea. The water surface there has been about 0.3 degrees hotter than normal since the mid-1990s. According to the study: "Computer models show this affects the regional air pressure, setting off a stationary wave in the atmosphere that arcs in a great circle from the tropical Pacific toward Greenland before turning back over the Atlantic."
Co-author John “Mike” Wallace, said, “Along this wave train there are warm spots where the air has been pushed down, and cold spots where the air has been pulled up, and Greenland is in one of the warm spots.” Wallace has documented the existence of decades-long climate variations in the Pacific Ocean resembling shorter-range El Niño variations in earlier studies.
The researchers are calling the climate changes due to greenhouse gases the "predictable part." The "unpredictable part," is the tropical Pacific region. Scientists don't know how long the Pacific Ocean is going to remain in its current state. This makes short-term forecasting difficult, but long-range forecasting may be made more accurate.
"If the Pacific temperature pattern shifts, warming in the Arctic could slow in coming decades, Ding said. There has already been evidence that this is the case, such as the jet stream pattern that hit the East Coast with an extremely cold winter this year. But human-driven global warming will probably outpace any natural cooling in the coming decades, according to the researchers.
The research was funded by the National Science Foundation, UW’s Quaternary Research Center, the National Basic Research Program of China and the APEC Climate Center. Other co-authors are Lei Geng at the UW; Ailie Gallant at Australia’s Monash University; and Hyung-Jin Kim at South Korea’s APEC Climate Center.
For more information, contact Ding at, Wallace at 206-543-7390 or, Battisti at 206-543-2019 or, and Steig at 206-685-3715 or
More about Greenland, Warming, Natural causes, Pacific ocean, Global warming
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