It's more than 3,600 miles from Tucson to the Arctic Circle, but researchers are starting to link some of Tucson's and the country's extreme cold and warm spells over the past few winters to the loss of Arctic sea ice that was caused by a warming climate.
A handful of peer-reviewed studies have been written by researchers nationally and internationally in the past few years, connecting Arctic sea ice loss to unusually cold and warm spells in winters across the U.S. and in northern Europe. The researchers acknowledge that their case is not proven and that more studies are needed.
But they believe that clear signs exist that the sea ice loss and other factors related to Arctic warming - which is occurring much faster than in the rest of North America - could be triggering a chain of atmospheric events that plays havoc with the jet stream. That's the common name for rapidly flowing air currents thousands of miles long and about six to nine miles above the Earth's surface that steer warm and cold air masses across the Earth.
"This research is very new, and there's a lot more to do. With the Arctic changing as dramatically as it is, I am certain there is some effect on the large-scale circulation, but the details are still to be worked out," said Rutgers University professor Jennifer Francis, who has been at the forefront of the research and the ensuing controversy.
One theory is that sea ice loss alters atmospheric patterns that cause the jet stream to swing north or south for prolonged periods, creating warm or cold spells that last days or weeks. In short, Arctic warming "essentially loads the dice" in favor of more wavy, erratic jet stream patterns, said professor Stephen Vavrus, a University of Wisconsin researcher who has worked on some of the studies.
Other scientists are skeptical. Professor Richard Seager at Columbia University's Lamont Doherty Earth Observatory said in an email, "So far I have heard Arctic sea ice loss invoked to explain cold northeast winters, U.S. summer heat waves, cold springs in the Southwest, Hurricane Sandy's path and more! A one-size-fits-all explanation for what, to me, looks like a run of bad weather."
Federal researcher Kevin Trenberth, of Colorado, says, "I think they've done some work which shows an association. I don't think they've demonstrated cause and effect. A lot of variations that occur, what goes on in the jet stream, is certainly related to what goes on in the Arctic, but whether the Arctic causes it is another matter."
A University of Arizona researcher who has followed this debate closely, Zack Guido, says the research on this topic is "cutting edge," and that the question of the impact of Arctic sea ice loss "is a big black box, a major area where people are scrambling to fill in some holes."
While it's hard or impossible, statistically, to link individual weather events or short-term trends to long-term climate change, the extreme weather that does occur is unfolding in a context of human-induced changes, he said.
"Think of it like a boat on an ocean," said Guido, a UA Institute for the Environment staff scientist. "The water is the climate and waves are the weather. If the water is rising, if the seas are rising, the waves will take you higher places than before."
How could melting Arctic ice make us colder - or warmer, for that matter?
"It can totally affect you," says Rutgers' Francis, who has authored or co-authored peer-reviewed studies on this subject.
Here's how, she says:
Since the temperature difference between the Arctic and elsewhere drives the jet stream's normal, west-east wind movements, an increase in that difference would be expected to force the jet stream to start swinging more wildly, north and south, triggering extreme weather patterns.
"That, in fact, we were able to document with our observations," said Francis. "The jet stream is that erratic."
These patterns could be caused not just by melting sea ice, but by other Arctic-related weather and air patterns caused by the region's temperatures warming much faster than the rest of this hemisphere - a pattern known as Arctic amplification. Another symptom is the transport of water vapor into the Arctic that itself is a greenhouse gas and also condenses into clouds, releasing latent heat and warming the atmosphere, she says. The clouds also trap the Arctic's newfound heat in the area, raising air temperatures further.
When the jet stream's north-south waves grow larger, cold Arctic air can penetrate farther south, as far as the U.S. Southwest, Francis says. In a northward swing, the jet stream can carry warm, tropical air away to the north, making this region warmer.
For example, right after a major cold blast froze crops and caused water pipes in Southern Arizona to burst in February 2011, researcher Guido wrote an article for UA's Southwest Climate Outlook publication saying that the jet stream had "looped farther to the south than normal, blasting Arizona and New Mexico with Arctic air."
This could be due to an influential climate force known as the "Arctic Oscillation" that could be changing due to a warming Arctic, Guido wrote.
Commonly called the AO, the oscillation is characterized by differences in atmospheric pressures over the Arctic and surrounding regions. When surface air pressures are lower over the Arctic and higher over the surrounding regions, the AO is felt to be in a positive phase blowing jet stream winds harder and more consistently from west to east. That keeps the Arctic air and winter storms farther north and the air down here warmer and drier.
When the air pressure trends reverse, the AO turns negative, jet stream winds slacken and the Arctic air blows in our direction, Guido wrote.
Jet Stream's erratic behavior
A federal study earlier this year found some merit to the sea ice-extreme weather link, concluding that wind patterns in the subarctic region from 2007 to 2012 had shifted from east-west to a more north-south, wavelike pattern. This pattern transports warmer air to the Arctic and pushes Arctic air farther south, possibly influencing the likelihood of persistent weather conditions farther south in North America and Europe, said the researchers led by James Overland, a National Oceanic and Atmospheric Administration oceanographer in Seattle.
But Columbia's Seager, a longtime climate researcher, said that most studies he's seen show that global warming is pushing west-to-east winds at least at the same speeds as before if not faster. He believes there is a lack of convincing computer model evidence to suggest that Arctic sea ice cover influences weather to any appreciable degree.
"Arctic sea ice has been declining for decades now, but despite this steady change, has only been invoked to explain weather events in recent years," said Seager.
One reason federal researcher Trenberth is uncertain about a sea ice loss-extreme weather link is that the ice loss occurs mainly in late summer and autumn, while the extreme weather patterns have been observed mainly in winter and early spring.
"By the time you get to November, the Arctic Ocean is filling up. In the winter, the Arctic Ocean is full,' said Trenberth, a senior scientist at the National Center for Atmospheric Research in Boulder. "It's hard to know how the (ice loss) translates into an effect on atmospheric circulation."
But while the maximum ice loss comes early, the temperature differences between the Arctic Ocean and the overlying air - which drives much of the jet stream's erratic behavior - occurs later in fall or in early winter, Wisconsin researcher Vavrus replied.
"The ocean is much warmer than the overlying atmosphere," he said. "That is important, because if you don't have as much ice cover as in past months, the energy from the ocean can reach the atmosphere, altering the circulation that way. If even a small amount of ocean that used to be ice covered is now open water that's very warm, these patterns can still occur."
Summing the issue up, UA's Guido said, "It's very easy to believe that changes in far off regions have an impact globally. The Arctic is rapidly changing. But I don't think we know exactly how changes in the Arctic will ripple through the climate system."
On StarNet: Read more environment-related articles at azstarnet.com/environment
• In Tucson this year, January and February's average temperatures were 2.8 and 4.5 degrees below normal, respectively. March and April together averaged 4.1 degrees above normal, making for the second warmest March-April on record. May is averaging at least 3 degrees above normal. In 2011, January and February again averaged below normal.
• This year saw Tucson's coldest Jan. 12 to Jan. 15 on record, averaging 18.5 degrees below normal. The average temperature for Jan. 1-16 was 8.6 degrees below normal - the fourth coldest spell on record for that period. A week later, the mercury hit or tied record highs for two days.
• In 2012, temperatures averaged above normal every month from January through May, closing with the seventh warmest May on record.
• On Feb. 2-3 of 2011, the temperature in Tucson stayed below freezing for an almost unheard of 18 straight hours. It only reached 38 on Feb. 3 and hit record low temperatures of 18 degrees on the 3rd and 4th.
• For the entire U.S., March 2012 was the warmest March on record. While Tucson basked in 80 degree weather this March, however, the Midwest, East and Southeast were battered with wave after wave of Arctic cold spells and snowstorms. In Chicago, the high temperature on March 20, 2012, was 85, while the high on March 20, 2013, was 25.
Sources: National Weather Service and Weather Underground
Arctic sea ice loss
• In recent years, Arctic air has warmed at least two times faster than in the rest of the Northern Hemisphere.
• European Space Agency satellites and University of Washington computer models have reported that the extent of summertime Arctic sea ice has plummeted by one-third over the past decade, and is about one-fifth of its total of 1980.
• Federal and University of Washington scientists predicted this year that most or all summertime Arctic sea ice will be gone by 2020, 2030 or 2060, based on different computer modeling approaches.
COMING NEXT SUNDAY
Southern Arizona farmers show how extreme weather events have affected their crops and livelihoods in recent years.
Contact reporter Tony Davis at firstname.lastname@example.org or 806-7746.