Sea ice off Antarctica and in the Arctic is at record lows for this time of year after declining by twice the size of Alaska in a sign of rising global temperatures, climate scientists say.
Against a trend of global warming and a steady retreat of ice at the Earth’s northern tip, ice floating on the Southern Ocean off Antarctica has tended to expand in recent years.
Now ice is shrinking at both ends of the planet, a development alarming scientists and to which a build-up of man-made greenhouse gases, an El Niño weather event that this year unlocked heat from the Pacific Ocean and freak natural swings may all be contributing.
Worldwide, this year is on track to be the warmest on record.
Combined, the extent of polar sea ice on December 4 was about 3.84-million square kilometres below the 1981-2010 average, according to United States National Snow and Ice Data Centre (NSIDC) satellite measurements. That is roughly the size of India or two Alaskas.
John Turner, of the British Antarctic Survey, said chilly westerly winds that sweep around the continent, perhaps insulating it from the effects of global warming, were the weakest for November in two decades. That may have let more heat seep south, he said.
A recovery of the high-altitude ozone layer over Antarctica, which led to cooler air over the continent when it was damaged by now-banned industrial chemicals, may also be a factor.
Turner said it was hard to pinpoint exactly what was happening.
“When we began getting satellite data from 1979 the sea ice started to decrease. Everyone said it was global warming … but then it started to increase again,” he said.
Accepting mainstream scientific findings and responding to increases in floods, heat waves and rising sea levels, almost 200 governments last year agreed to phase out fossil fuels and limit the global temperature rise above pre-industrial levels to less than 2˚C.
The polar regions are radically different from each other because the Arctic is an ocean ringed by land and Antarctica is a vast land mass surrounded by water.
Ice around Antarctica, retreating with a summer thaw, is the smallest for early December at 11.22-million square kilometres, beating a record from 1982, NSIDC data show.
Anders Levermann, a professor at the Potsdam Institute for Climate Impact Research, said the low polar sea ice pointed to man-made warming. “It’s an extraordinary departure from the norm,” he said.
Scientists say Antarctica’s glaciers could slip more quickly into the ocean, speeding up the pace of sea- level rise, if there is less ice floating on the sea to hold them back.
Arctic sea ice, expanding in winter, is at a low of 10.25-million square kilometres, below the 2006 record.
The Mail & Guardian last week reported that, according to the Arctic Resilience Report, the effects of changes in the Arctic will have a “substantial” effect the rest of the world.
With a global climate system that is always struggling to reach some sort of equilibrium, changes far away can trickle across the globe.
The Greenland ice sheet usually takes thousands of years to respond to the changing climate, but in the past few years its ice has started to thin away. That melt trickles through the ice sheet and creates cracks that expose more parts of the sheet to heat. The warmer ocean also nibbles away at the edges of the ice sheet. If the whole ice sheet melts, it will raise global sea levels by an average of 7.4m. Not good for South Africans living in coastal settlements.
What happens next is too unpredictable to compute. For South Africa, research by the environmental department shows that the high pressure systems, that bring rainfall, will move further away with warming oceans.
That will mean less but heavier rainfall.
What is certain, and what the report warns of, is that global change is happening because the Arctic is warming at too quick a rate for plants and animals to adapt. — Reuters, additional reporting by Mail & Guardian reporter