Guest post by David Middleton
From the No Schist, Sherlock files…
The “record low wintertime maximum extent” still looks pretty icy.
Natural swings in the Arctic climate have caused up to half the precipitous losses of sea ice around the North Pole in recent decades, with the rest driven by man-made global warming, scientists said on Monday.
The study indicates that an ice-free Arctic Ocean, often feared to be just years away, in one of the starkest signs of man-made global warming, could be delayed if nature swings back to a cooler mode.
Natural variations in the Arctic climate “may be responsible for about 30–50 percent of the overall decline in September sea ice since 1979,” the U.S.-based team of scientists wrote in the journal Nature Climate Change.
Sea ice has shrunk steadily and hit a record low in September 2012 — late summer in the Arctic — in satellite records dating back to 1979.
The ice is now around the smallest for mid-March, rivaling winter lows set in 2016 and 2015.
The study, separating man-made from natural influences in the Arctic atmospheric circulation, said that a decades-long natural warming of the Arctic climate might be tied to shifts as far away as the tropical Pacific Ocean.
“If this natural mode would stop or reverse in the near future, we would see a slow-down of the recent fast melting trend, or even a recovery of sea ice,” said lead author Qinghua Ding, of the University of California, Santa Barbara.
But wait! What’s that? It looks like an ominous email!!!
But in the long term the build-up of man-made greenhouse gases would become an ever more overwhelming factor, he wrote in an e-mail.
Oh no!!! A scientist “not involved in the study” is now confirming the ominous email!!!
“Looking ahead, it is still a matter of when, rather than if, the Arctic will become ice-free in summer,” said Ed Hawkins, of the University of Reading, who was not involved in the study.
“This is the worst of the worst catastrophes in the world! Oh, it’s crashing … Oh, the humanity! Honest, I can hardly breathe. I’m going to step inside where I cannot see it.”
Please say it ain’t so!!!
The melt of the Arctic is disrupting the livelihoods of indigenous peoples and damaging wildlife such as polar bears and seals while opening the region to more oil and gas and shipping.
On a somewhat more serious note…
The Arctic has seen rapid sea-ice decline in the past three decades, whilst warming at about twice the global average rate. Yet the relationship between Arctic warming and sea-ice loss is not well understood. Here, we present evidence that trends in summertime atmospheric circulation may have contributed as much as 60% to the September sea-ice extent decline since 1979. A tendency towards a stronger anticyclonic circulation over Greenland and the Arctic Ocean with a barotropic structure in the troposphere increased the downwelling longwave radiation above the ice by warming and moistening the lower troposphere. Model experiments, with reanalysis data constraining atmospheric circulation, replicate the observed thermodynamic response and indicate that the near-surface changes are dominated by circulation changes rather than feedbacks from the changing sea-ice cover. Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30–50% of the overall decline in September sea ice since 1979.
Perspective: NSIDC Arctic Sea Ice Index Interactive Graph
The five earliest years of data plot near +2 standard deviations. The five most recent full years of data plot near or just outside of -2 standard deviations. Ding et al., 2017 conclude that up to half of the difference is due to the NAO and other natural climate fluctuations.