Qinghua Ding, of the University of California sheds more light on the Arctic climate.
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.
Part of the decline in ice cover is due to ‘random’ and ‘chaotic’ natural changes in air currents, researchers said, with the rest being driven by man-made global warming, scientists said.
The findings could help narrow down huge uncertainties about when the ice will vanish.
In 2013, a U.N. panel of climate scientists merely said human influences had ‘very likely contributed’ to the loss of Arctic ice, without estimating how much. It said that the ice could disappear by mid-century if emissions keep rising.
The research means that although it is widely feared that the Arctic could soon be free of ice, this could be delayed if nature swings back to a cooler cycle.
Loss of the sea ice is predicted to have numerous effects on the planet: these include reflecting less light into space, potentially making the earth warmer and more predictable.
It will also reducing the habitat of animals such as polar bears.
Sea ice hit a record low in September 2012 – late summer in the Arctic – in satellite records dating back to 1979, and declines by around 10 per cent each year. The ice is now around the smallest for mid-March, rivalling 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.
Lead author Qinghua Ding, of the University of California, Santa Barbara, said: ‘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.
The new model demonstrates that since 1979 a shift in wind patterns is responsible for about 60 percent of sea ice loss in the Arctic Ocean. Much of this shift is related to climate change, but the study finds that 30 to 50 percent of the observed sea ice loss is due to natural variations in this large-scale atmospheric pattern.
According to the researchers, the long-term cycles are thought to be driven by the tropical Pacific Ocean. Conditions there, set off ripple effects, causing stationary atmospheric waves to snake around the globe and create areas of higher and lower air pressure.
Whether the atmosphere will stay in its current phase is unknown.
It could enter an opposite phase in which a low-pressure atmosphere over Arctic seas would cancel out much of the increased melting due to climate change. But in the long term the build-up of man-made greenhouse gases would become an ever more overwhelming factor, he said.
The average temperature last month was 7.3 degrees warmer than normal the National Oceanic and Atmospheric Administration reported Wednesday.
Looking ahead, it is still a matter of when, rather than if, the Arctic will become ice-free in summer.’
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.
Some plants in the low Arctic of Greenland are emerging sooner than usual while others are delaying their emergence as warmer winters are causing spring to come sooner. These changes are associated with reduced sea ice cover in the Arctic and are causing ‘nature’s clock’ to speed up.
After Antarctica, Greenland’s ice cap contains the second largest mass of frozen freshwater in the world. The ice sheet ice sheet covers 1,710,000 square km, or roughly 80 per cent of the surface of Greenland.
Currently, melting ice around Greenland is thought to account for around 10 per cent of sea level rise. Researchers estimate half of Greenland’s outlet glaciers could undergo significant melting. A UCI and NASA study shows southern Greenland’s ragged, crumbling coastline is scored by more than 100 canyons beneath glaciers that empty into the ocean.
Professor Andrew Shepherd, of Leeds University, who did not participate in the study, welcomed it as pinning down the relative shares of natural and man-made influences.
Nobody’s done this attribution before,’ he said.
Chris Rapley, Professor of Climate Science at University College London, said: ‘Over the last 3 decades satellite instruments have measured a 3% per decade loss of summer minimum sea ice extent in the Arctic. Models have consistently underestimated the loss.
The new paper by Ding offers an explanation of the discrepancy. The authors provided evidence of a process by which the decadal timescale of natural variability in the Arctic atmospheric circulation may have contributed as much as 30-50% of the decline.
Even so, the systematic component of loss, due to human-induced climate change remains robust and significant, and should not be underestimated.
‘The possibility that the atmospheric variability in the Arctic is ‘teleconnected’ to changes in the tropical Pacific, illustrates the complexity of the global coupled ocean-atmosphere-ice system and its capacity to deliver ‘surprises’.