Warming Arctic linked to polar vortex outbreaks farther south
Warmer air weakens the vortex, which normally keeps cold air trapped in Arctic, letting it go south
Warming of the Arctic caused by climate change has increased the number of polar vortex outbreaks, when frigid air from the far north bathes other parts of the Northern Hemisphere in killer cold, a study finds.
The study published this week in the journal Science is the first to show the connections between changes in the polar region and February's Valentine's Week freeze that triggered widespread power outages in Texas, killing more than 170 people and causing at least $20 billion US ($25 billion Cdn) in damage. Extremely cold temperatures also hit much of Canada that month.
The polar vortex normally keeps icy air trapped in the Arctic. But warmer air weakens the vortex, allowing it to stretch and wander south. The number of times it has weakened per year has more than doubled since the early 1980s, said study lead author Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside of Boston.
"It is counterintuitive that a rapidly warming Arctic can lead to an increase in extreme cold in a place as far south as Texas, but the lesson from our analysis is to expect the unexpected with climate change," Cohen said.
Climate scientists are still debating how and whether global warming is affecting cold snaps. They know it's reducing the overall number of cold days, but they are still trying to understand if it leads to deeper cold snaps.
Cohen's study is the first to use measurements of changes in the atmosphere to help explain a phenomenon that climate models had struggled to account for.
The study "provides a potentially simpler interpretation of what's going on," said Pennsylvania State University climate scientist Michael Mann, who wasn't part of the study.
Cohen was able to show how there have been dramatic differences in warming inside the Arctic itself, which drives how the polar vortex can stretch and weaken.
When the area north of England and around Scandinavia warms more than the area around Siberia, it stretches the polar vortex eastward and the cold air moves from Siberia north over the polar region and then south into the central and eastern part of the United States.
"The Texas cold blast of February 2021 is a poster child" for the link between a changing Arctic and cold blasts in lower latitudes, said climate scientist Jennifer Francis of the Woodwell Climate Research Center on Cape Cod in Massachusetts. She helped pioneer the Arctic link theory, but wasn't part of Cohen's research.
"The study takes this controversial hypothesized linkage and moves it solidly toward accepted science," she said.
Global warming threatens the existence of an Arctic oasis
The University of Helsinki's Environmental Change Research Unit (ECRU) took part in an international study investigating the millennia-long history of the most important oasis in the Arctic and the potential effects of climate change on its future.
The North Water Polynya is an area of year-round open water located between northwest Greenland and Ellesmere Island, Canada, in northern Baffin Bay, which is otherwise covered by sea ice roughly eight months of the year. The area is known as an Arctic oasis, and one of the main migration routes of Greenland's original population runs just north of the area.
In the study, microfossils and chemical biomarkers preserved in marine and lake sediments were analyzed as keys to the past, exposing historical variation in the North Water Polynya in the past 6,000 years.
The polynya's high rate of primary production, for which, in marine environments, diatoms and other microalgae are responsible, maintains a diverse and unique ecosystem that serves as a safe haven for a range of species in Arctic conditions, which are otherwise harsh. Keystone Arctic species, such as the polar bear, the walrus and the narwhal, also thrive there. For the indigenous populations reliant on hunting and fishing, this area, the largest polynya in the northern hemisphere, has been a lifeline.
According to the study, the polynya was stable and its primary production was high roughly 4,400–4,200 years ago, at the time when people arrived in Greenland from Canada over the frozen Nares Strait.
A millennium of instability and new heat records
However, the polynya's stability has varied over the last millennia: during the warmer climate periods 2,200–1,200 years ago, the area was unstable and its productivity fell drastically. When primary production rates are low, significant reductions are seen in the populations of organisms in the upper levels of the food web, such as zooplankton, fish and marine mammals.
"According to archaeological finds, there were no inhabitants in the area during this period. It's a mystery that can potentially be explained, in light of the research findings, by conditions that were unfavorable to people reliant on hunting and fishing," says researcher Kaarina Weckström from the Environmental Change Research Unit, University of Helsinki.
The researchers point out that air temperatures have never reached the current level in northwest Greenland in the 6,000-year-long period of the polynya's history studied. Global warming and reduction in sea ice caused by human activity have led to the polynya's instability. The area is maintained by favorable ocean currents and winds, and particularly by an ice bridge located north of the polynya, which prevents drift ice in the Arctic Ocean traveling further south. It is the annual formation of this natural block that the warming of the climate is now threatening.
"This area, the Arctic's most important oasis, is likely to disappear if temperatures continue to rise as forecast. It would be important to at least slow climate change down, in order for Arctic indigenous peoples to have some kind of a chance to adapt to their future living conditions. Then again, as the history of the polynya suggests, if we can reduce greenhouse gas emissions and mitigate the rising air temperature, both Arctic sea ice and the polynya can be restored," Weckström sums up.
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