- Scientists predominantly believe that the tropics have the largest influence on global weather, but new research suggests that climate change-driven Arctic heating and rapid melting of Arctic sea ice could impact places as far away as the equator.
- A new study, published today, found that accelerating ice melt in recent decades could be linked to Central Pacific trade wind intensification, the emergence of El Niño events, and a weakening of the North Pacific Aleutian Low Circulation — a semi-permanent low pressure system that drives post-tropical cyclones and generates strong storms.
- A 2019 study likewise revealed a close connection between winter Arctic ice concentration over the Greenland-Barents Seas and the El-Niño-Southern Oscillation (ENSO) in the following winter. Another study out this month found that in prehistoric times, periods of major permafrost thawing were tied to an absence of Arctic summer sea ice.
- Other research has drawn connections between rising Arctic temperatures and changes in the jet stream — a fast-moving river of air that circles the northern polar region. A slowing of the jet stream, and its looping far to the south, is thought to be stalling temperate weather patterns, worsening droughts, storms and other extreme weather.
Melting Arctic sea ice has fundamentally and profoundly altered polar ecosystems in recent decades, creating warmer temperatures on land and disrupting the behavior of marine mammals and ice-obligate species. But now new research suggests that melting sea ice is also influencing weather systems as far away as the equatorial Pacific Ocean.
Patterns originating in those tropical waters include El Niño and La Niña, which shape the weather experienced on every continent, meaning, if the new study is correct, that Arctic ice loss could have global ramifications.
At the end of summer 2019, Arctic sea ice extent was tied with 2007 and 2016 as the second lowest since satellite records began in 1979. Compared to the 1981-2010 average, ice extent has declined by a third, and volume has also dropped precipitously. A study published today in the Proceedings of the National Academy of Sciences finds this accelerating sea ice melt could be linked to the intensification of Central Pacific trade winds, the emergence of El Niño events, and a weakening of the North Pacific Aleutian Low Circulation — a semi-permanent low pressure system that drives post-tropical cyclones and generates strong storms.
Using computer analysis of historical sea ice data, two researchers at the University of California, San Diego identified which atmospheric phenomena seemed to be changing alongside the retreat of Arctic ice. Notably, they found that as the ice vanished, Central Pacific trade winds intensified.
The scientists hypothesize that the melting ice triggers a series of events that shoot cold air toward the equator via the upper atmosphere: In the absence of sea ice, the warming ocean creates a rising column of air that travels vertically to the boundary of the troposphere and stratosphere, where it is then pushes south, flowing through the mid-latitudes and on to the equator.
“It’s like applying a candle to the bottom of the atmosphere; you set off convection that rises to high altitudes and once it gets up there it has no place to go, so it gradually moves southward,” explains Charles Kennel, one of the study authors and former director of the Scripps Institution of Oceanography.
The effect was witnessed most strongly in models comparing a high ice-loss region north of the Siberian Arctic coast and the Intertropical Convergence Zone in the Pacific where the trade winds of the Northern and Southern hemispheres join. This is one of the first studies to find evidence that melting Arctic sea ice could be influencing weather systems as far south as the tropics. However, the current research, while it shows historical concurrence of Arctic and tropical changes, it does not prove causation.
Whether Arctic sea ice melt affects weather systems farther south has long been the subject of contentious debate in the scientific community. In 2012, Jennifer Francis, a senior scientist at the Woods Hole Research Center in Massachusetts, USA, published a study that drew connections between changes in the Arctic and mid-latitude extreme weather. Her work “triggered off a very large movement in the [scientific] literature which people are still warring about,” says Kennel. “This has been very controversial, but the evidence is piling up on [Francis’] side.”
Researchers are increasingly certain that the extreme temperature difference between the Arctic and temperate zone farther south is one of the primary factors that drives the jet stream — a fast-moving river of air that circles the polar region in the Northern Hemisphere. But as sea ice vanishes and Arctic temperatures increase, the temperature difference between these regions is getting smaller.
That means there’s less force driving jet stream winds from west to east, causing the weakened air flow to start wildly deviating from its typical polar path and looping deeply into lower latitudes. Francis’ theory proposes that the loopy, lower energy jet stream is altering historical weather patterns, causing major storms and droughts to stall in place. For example, this complex jet stream effect may have intensified the record rains and flooding brought by stalled Hurricane Harvey in 2017 and Florence in 2018.
When Kennel reviewed the research on possible mid-latitude influences, he thought, “Gosh, if the effect is that big and it already gets to 45 degrees latitude, how come the [atmospheric] waves that carry all of this energy don’t get to the equator? Why should it just stop there?”
Francis, who served as a reviewer of the PNAS paper, notes that Kennel’s study “provides new and compelling evidence that rapid Arctic change is affecting weather patterns even into the tropics. Traditional meteorological wisdom has long considered the tropics to be the dominant player in controlling major weather patterns, but this and other new studies suggest it’s time to also look at the north.”
Another study published last year in Climate Dynamics revealed a close connection between winter Arctic ice concentration over the Greenland-Barents Seas and the El-Niño-Southern Oscillation (ENSO) in the following winter.
“These results present yet more evidence for human-caused climate change affecting a major source of extreme weather, along with a silver lining that by knowing how much ice is lost in summer may help predict ENSO the following winter,” says Francis.
Kennel notes that prior to 1999, most El Niños formed off the coast of Peru, well below the equator. “They came at Christmas and were given the name El Niño [Little Boy, or Christ Child, in Spanish] by Peruvian fishermen because they thought the warming and change in fisheries was associated with Christmas,” says Kennel. “Now we’re finding that many more El Niños are initiated in the Central Pacific. It’s the first indication that some El Niños in the December/January period can be triggered by the arrival of Arctic air.”
New research also shows that the loss of Arctic sea ice has dire implications on land, impacting the surrounding tundra which serves as one of the largest reservoirs of stored carbon on the planet. Scientists believe that for every one degree Celsius (1.8 degree Fahrenheit) rise in Earth’s average temperature, thawing permafrost may release the equivalent of four to six years’ worth of coal, oil and natural gas carbon emissions.
In a Nature study published earlier this month, researchers found that in prehistoric times, periods of major permafrost thawing were tied to an absence of summer Arctic sea ice. “This discovery about the past behavior of permafrost suggests that the expected loss of Arctic sea ice in the future will accelerate [thawing] of the permafrost presently found across much of Siberia,” says Gideon Henderson, one of the study’s authors.
This growing body of work adds weight to a major emerging concern related to Earth’s bioregional interconnectedness. Scientists worry that in the future, when one bioregion reaches a climate tipping point, a domino effect could occur, triggering tipping points in other faraway places. While more research is needed, scientists point to potential cascading effects that could link rapid Arctic and Antarctic ice loss, permafrost thaw, boreal forest fires, the stalling of Atlantic Ocean circulation, coral reef die-offs, and intensifying Amazon drought.
Kennel stresses the newly identified link between the Arctic and the tropics merits further research. But this work points the way.
Kennel, C. F., & Yulaeva, E. (2020). Influence of Arctic Sea-Ice Variability on Pacific Trade Winds. Proceedings of the National Academy of Sciences, 117(4)
Banner image caption: A sea turtle swims in the tropics. Its future could be influenced by melting sea ice in the faraway Arctic Ocean. Image by Anthony C found on flickr CC BY-NC-ND 2.0.
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