It’s got opportunity. There are fingerprints on the weapon. But what is the motive?
In a finding consistent with rising concentrations of greenhouse gases in the atmosphere, warm water oozing north from the Atlantic Ocean has once again been fingered as a prime suspect in the generation-long murder of Arctic ice.
In this instance, a remarkable study from Rutgers Institute of Marine and Coastal Studies found rising sea-surface temperatures in the Barents Sea as the factor liquidating winter ice cover northeast of Scandinavia.
And then the feedback mechanism kicks in. Less ice in winter leads to less ice in summer, with amplified warming of the sea, which in turn leads to even less ice in following winters. The meltback snowballs, in a manner of speaking.
“In the Barents Sea, I expected more influence from atmospheric heating; but it [the retreat of the ice edge] seems to be governed almost entirely by warming from the ocean,” said Jennifer Francis, associate research professor, in a story posted by the Institute.
Not so with the Bering Sea near Alaska.
The Bering Sea — as any wind-battered, rain-soaked coastal Alaskan will tell you — gets slapped around by the position and intensity of the Aleutian Low. That’s the perpetual cyclonic system that drives much of Alaska’s weather and lobs a series of fall storms that rival hurricanes in total power and local winds speeds.
As Francis and colleague Eli Hunter wrote in Drivers of declining sea ice in the Arctic winter: A tale of two seas, the two Arctic bodies have responded differently to recent climate shifts.
“Between 1979 and 2005 in the Bering Sea, the ice edge is influenced mainly by anomalies in easterly winds associated with the Aleutian Low, which was particularly strong during the 1980s,” they wrote in the abstract appearing Geophysical Research Letters. “The Barents Sea ice edge, in contrast, is driven primarily by two factors: anomalies in sea-surface temperature, particularly close in time to the maximum extent, and by southerly wind (from the south) anomalies integrated back to mid- and early winter.”
Sea surface temps in the Barents have risen more than 5 °F since 1980, largely du Francis says it’s clear that the ice pack — now setting all-time records for its summer shrink — will continue to decline.
“The hemispheric-mean decline in winter ice extent is due in large part to increasing sea-surface temperatures in the Barents Sea and adjoining waters, which are consistent with increased concentrations of greenhouse gases,” Francis and Hunter concluded.
Here’s more in a release from Rutgers University:
Scientists have known for some time that the extent of perpetual, summer ice cover in the Arctic has been shrinking, but until the past few years, the average amount of winter ice has been relatively steady.
The winter ice amount is important because if it begins to decrease, scientists believe it is an indicator that enough extra heat from the sun is being absorbed in summer in new open water areas so that the ice grows less in winter and is more easily melted the following summer, leading to even less summer ice.
The record-breaking ice loss this year is further, dramatic evidence that this process is underway.
While satellites can see the recent winter ice retreat, no one knew until now what was driving the ice back. Francis said she and Hunter were surprised when they discovered that warming ocean temperatures – and not atmospheric effects – were the main source of winter ice retreat, and that the warming is linked to general rising temperatures of the Atlantic Ocean via the Gulf Stream, which brings Atlantic water into the Barents Sea.
“In the Barents Sea, I expected more influence from atmospheric heating; but it [the retreat of the ice edge] seems to be governed almost entirely by warming from the ocean,” Francis said.
This satellite view of sea ice in the Barents Sea
includes the island of Novaya Zemlya
with the solidly frozen Kara Sea to its east.Source: NASA Visible Earth
Should the warming trend continue — and all indications are that it will — there would be considerable economic and political implications.
“Fishing, shipping, oil exploration will all be easier to do in the Arctic if there is less ice around for a shorter time,” Francis said.
Francis and Hunter were in for another surprise in the Bering Sea, between Alaska and Siberia. That sea is virtually cut off from the Pacific Ocean by the Aleutian Islands. The researchers expected the ice edge there to be pushed around by northerly and southerly winds, but that wasn’t the case.
Instead, it was the strength or weakness of the Aleutian Low — a semi-permanent storm with predominantly easterly winds in much of the Bering Sea — that determined the ice edge.
In years when the low was weak — when the east wind didn’t blow as hard — the ice edge crept farther south. In years when the east winds blew hard, the ice edge retreated northward. The strength of the Aleutian Low oscillates in cycles lasting 10 to 20 years, Francis said, and right now, appears to be in a weak cycle.
That means that the ice edge in the Bering Sea, not exposed to the world’s ocean system like its Barents Sea counterpart, has not retreated as much. Computer models predict, however, that the Aleutian Low will strengthen as the global climate system adapts to increasing greenhouse gases.
