Australian scientists document early start to melt season
Australian scientists say Antarctic sea ice started its annual spring retreat early this year and has set new daily record lows for extent during late September — during the Austral spring, when Antarctic sea ice is at a maximum.
In a press release, the Antarctic Climate & Ecosystems Cooperative Research Centre said the sea ice extent started its annual retreat early, just two years after winter sea ice extent around Antarctica reached a new record high in September 2014, when it exceeded 20 million square kilometres for the first time since satellite measurements began in 1979.
This year, Antarctic sea ice began its annual spring retreat about four weeks earlier than average, after peaking at 18.5 million square kilometres on 28 August 2016, which was close to the lowest winter maximum on record.
“This is a reversal of the recent trend towards record high winter sea-ice extent over the past few years,” said Dr Jan Lieser. “Within the space of just two years, we have gone from a record high winter sea-ice extent to record daily lows for this point in the season. This is a fascinating change, and a great reminder that we are dealing with an extremely variable component of the climate system. It’s also a reminder of why it can be unwise to leap to conclusions about the link between Antarctic sea ice and climate change on the basis of one or two years of data,” he said. “It is the long-term trends that are most important, as well as the regional variability, which is high around Antarctica.”
Sea-ice has an important effect on the global climate system and ecosystems, by covering and affecting up to 40 percent of the Southern Ocean surface area during winter. The annual cycle of advance and retreat represents one of the greatest seasonal changes to the Earth’s surface, and has far-reaching impacts on atmosphere-ocean interactions and the Earth’s climate.
Lieser said that the lingering effects of the strong El Niño probably played a role in shaping Antarctic sea ice distribution, but that local weather patterns also have an effect. The ups and downs of the Antarctic sea ice stand in contrast to the steady downward trend in the Arctic, but climate models project that Antarctic sea ice will also decline dramatically in the long term, up to 60 percent by 2200.
The recent measurements reported by the Australian scientists came during a time of year when sea ice conditions around Antarctica are particularly variable, said Dr. Ted. Scambos, a leading ice researcher with the Boulder-based National Snow and Ice Data Center, which tracks Antarctic sea ice here.
“With the sea ice spread around Antarctica over such a broad area, storminess and changes have have a large effect by shoving the ice edge southwards (or northwards) over a large arc of the perimeter,” Scambos said.
A recent study in the journal Nature Communications reinforced the expected long-term decline by comparing today’s temperatures with those of about 128,000 years ago — the last time Earth was as warm as it is today. During that era, Antarctic sea ice extent was about 65 percent smaller than now, according to the study.
The sea ice helps buffer the Antarctic continent from warming ocean waters. If the sea ice dwindles, warmer air and water would intrude over and under the West Antarctic ice sheet, it could “pre-condition the ice sheet for collapse,” according to Holloway.