SOURCE: Inside Climate News

DATE: January 27, 2020

SNIP: The rapid decline of Arctic sea ice during the last couple of decades has spurred climate scientists to study how that meltdown influences the rest of the planet, and a new study suggests that the effects may extend deep into the tropics.

The study, published Monday in the journal Proceedings of the National Academy of Sciences, detected a pattern that links sea ice decline since the late 1990s with more frequent warm cycles in the Central Pacific Ocean. The surges of ocean heating in that region can disrupt the climate, affecting drought, flood and hurricane patterns around the world.

Winds are the link between the melting ice and the tropics. The researchers posit that the Arctic Ocean has warmed up so much in the last 20 years that warm, late-summer sea surface air forms powerful convective towers, rising to the stratosphere. When the air falls back toward the equatorial Pacific, it intensifies prevailing east-to-west trade winds that push warm water toward Asia and Oceana, giving birth to a Central Pacific El Niño, a geographically specific variation of the well-documented Pacific warming and cooling cycle that is a key driver of the global climate.

The study found a secondary effect. The atmospheric roller coaster rebounds back north, and may weaken a weather pattern near Alaska that steers Pacific storms toward the West Coast.

The new research shows that El Niños forming in the Central Pacific started becoming more frequent at the same time that Arctic sea ice extent started its precipitous decline.

Jennifer Francis, a climate researcher with the Woods Hole Research Center who was not involved in the study, said the findings add to, “a growing body of evidence suggesting that the influence of Arctic sea-ice loss on large-scale wind systems reaches farther than thought, beyond the mid-latitudes and into the tropics.”

It’s hard to imagine that the rapid decline of sea ice, the planet’s heat-reflecting polar shield, doesn’t change weather patterns in other regions, said Charlie Kennel, former director and professor emeritus at the Scripps Institution of Oceanography and a co-author of the new study.

“There’s a definite relationship and a change in tropical climate,” Kennel said.

Here’s how the connection works. As sea ice dwindles, larger areas of ocean water are exposed to the sun for much longer periods. Ocean water is darker than ice, and absorbs about 93 percent of the incoming heat (ice reflects up to 80 percent back to space).

According to the study, that warmer water creates convection—rising air—that goes to the top of the lower atmosphere, where it has “nowhere to go but south,” Kennel said. That movement goes hand-in-hand with recent shifts in weather patterns that have caused extreme cold outbreaks in the central U.S. and deadly flooding in Asia, he added.

In a secondary, complex link, that vertical wave of air is then reflected northward again, possibly weakening the Aleutian low, a persistent weather pattern that usually spins off the southern coast of Alaska, steering storms toward the West Coast. Kennel said the impacts of that weakening aren’t yet fully understood, but may be related to the recent dramatic decline of sea ice in the Bering Sea.

A related 2017 study suggested that the chain of events caused by dwindling Arctic sea ice could reduce winter rainfall in California. In a hemisphere-spanning, two-step connection, “sea-ice changes lead to reorganization of tropical convection that in turn triggers an anticyclonic response over the North Pacific, resulting in significant drying over California,” the researchers wrote in the journal Nature Communications.