Significant melting of Arctic sea ice is linked to changing global weather patterns, but climate scientists still have a lot of unanswered questions.
“The Arctic is changing fairly rapidly,” NOAA’s Pacific Marine Environmental Lab oceanographer Dr. James Overland said, citing the record low ice extent in November 2016.
In addition to setting a record low in November, Arctic sea ice extent averaged around 4.67-square miles for December 2016, ranking second for the lowest extent in the satellite data record dating back to 1979, according to research published by the National Snow and Ice Data Center (NSIDC).
One of the ways Arctic sea ice melt may be impacting weather patterns is due to the reduced temperature difference between the Arctic region and the mid-latitudes, which could favor the weakening of the polar jet stream, AccuWeather Meteorologist Brett Anderson said.
Acting as a highway in which storm systems travel along, the jet stream is a fast river of air high in the atmosphere that marks the boundary between cool air to the north and warm air to the south.
“When the polar jet stream weakens it can increase the chances of a ‘blocking’ pattern over the far north,” Anderson added. “These blocking patterns can end up forcing the jet stream to buckle, allowing Arctic air to push much farther south than normal.”
The blocking patterns can also favor the development of unusually strong, slow-moving storms in the mid-latitudes, which lead to extremes in weather such as blizzards, floods and major wind events, Anderson said.
Overland said this impact on the eastern United States was noticeable in December 2016, but other factors such as warmth gripping Alaska and the eastern Pacific can also cause variations in eastern North America.
Overland explained that it has been difficult for scientists to sort out the Arctic impacts from other natural variability in weather patterns.
What is known is that the Arctic is warming more rapidly than models predicted and at a rate more than double that of the rest of the world, Overland said.
For years, scientists could find Arctic ice floes upwards of 10 years old, NSIDC Director Mark Serreze said.
“You really don’t see that anymore,” Serreze said. The Arctic sea ice has not only seen significant melting in recent years, he said, the ice is now younger and thinner than it once was.
Younger sea ice is much more susceptible to completely melting during the summer, Anderson said.
With increased ice melt, the Arctic also opens up a dark ocean surface, allowing for the absorption of more sunlight. In turn, this causes more of a warming effect, which makes it an entirely different system than the large, thick ice sheet of the continental Antarctic, Serreze said.
Serreze said many extreme precipitation events can also be attributed to more atmospheric water vapor, but the overall impacts in global weather resulting from a warming Arctic is unknown.
It is difficult to link any one severe weather event to changes in climate or a warming Arctic, Anderson added. Overland agreed, stating there is not a one-to-one correlation since the changes are extremely complex.
Other factors like rising air temperatures, sea surface temperatures and the influence of the tropics in addition to Arctic ice melt all play a role in weather patterns.
Two other major influences on weather are patterns like El Niño and the North Atlantic Oscillation. According to Overland, by studying all of these factors working in tandem with a warming Arctic, its influence may be clearer.
“El Niño is the abnormal warming of the sea surface waters along the equatorial Pacific due to changes in tropical wind patterns,” Anderson said.
During El Niño, changes in ocean temperatures and wind patterns can alter the strength and position of the jet stream, leading to weather extremes over certain regions of the world.
The NAO, or North Atlantic Oscillation, is made up of two pressure centers over the North Atlantic. According to Anderson, during the positive phase of the NAO, Arctic air is prevented from building south into the U.S.
During the negative phase, the influx of Pacific air is shut off and cold air can flow into Canada and the eastern U.S.
A study found that the recent reduction of Arctic sea ice in the late autumn may favor more of a shift to a negative NAO phase during the winter, Anderson said.
It is clear that the Arctic will continue to warm and that this process will have a noticeable effect on global weather in the long term, Overland said. Eastern North America is likely to have more weather extremes, he added.
Rising sea levels as well as extremes in heat waves, rainfall, drought, blizzards and hurricanes may all become more common in the coming decades as the climate continues to change, Anderson said.
By Michael Kuhne | www.accuweather.com