Dramatic loss of sea ice around Antarctica

At its lowest level for September since records began, satellite imagery shows.

Robbie Mallett, of Manitoba University, said there were ‘very good reasons to be worried’. Picture: Robbie Mallet

Sea ice surrounding Antarctica is at its lowest level for September since records began, satellite imagery shows.

Scientists have described the degree of melting as “almost mind-blowing”.

The continent is covered in a sheet of ice that is 2.1km thick on average. The surrounding ocean carries floating ice across as much as 11 million square kilometres during the southern winter from June to September.

Satellite data shows the sea ice surrounding Antarctica covers an area about 965,000 square kilometres less than the September average. “It’s so far outside anything we’ve seen, it’s almost mind-blowing,” Walter Meier, who works for the National Snow and Ice Data Centre, told the BBC.

Scientists are trying to understand why sea ice coverage has dropped so dramatically. Antarctica was previously thought to be relatively resistant to global warming. Until 2016, sea ice had been spreading around Antarctica but in three of the previous seven years, the amount of sea ice has broken records, falling to the lowest levels seen since satellites started gathering data in the 1970s.

Scientists are considering whether an unusual combination of natural factors might have caused this year’s recession and how much of a role human-driven climate change is playing.

Robbie Mallett, of Manitoba University in Canada, said: “There is a chance that it’s a ­really freak expression of natural variability.” He said a shortage of historical data made it difficult to analyse long-term trends.

Some troubling events have been recorded in recent years on the icy continent. In March last year, temperatures in east Antarctica were at minus 10C when they should have been closer to minus 50C. For Antarctica, this could be considered an extreme heatwave.

Martin Siegert, of Exeter University, said when he started studying the Antarctic 30 years ago, scientists thought extreme weather events could never happen there. He wondered if warming caused by humans could be “awakening this giant of Antarctica”. Professor Siegert said this would be “an absolute disaster for the world”.

The expanse of ice in the southern region helps to regulate temperatures, reflecting back some of the sun’s energy.

Since the 1990s, loss of land ice on Antarctica has contributed 7.2mm to ocean levels. Much is unknown about the sea ice around Antarctica but Dr Mallett said there were “very, very good reasons to be worried”.

He added: “It’s potentially a really alarming sign of Antarctic climate change that hasn’t been there for the last 40 years and is only just emerging.”

A paper this month in the journal Nature said observations “suggest ocean warming has played a role in pushing Antarctic sea ice into a new low-extent state”. It found a “multi-decade increase in Antarctic sea ice” had “peaked” between 2014 and the spring of 2016. Dr Mallett said of the continent’s shroud of sea ice: “We can see how much more vulnerable it is.”

The Times