24th December 2016
Record low sea ice cover
The National Snow and Ice Data Centre (NSIDC) has announced record low sea ice extents for both the Arctic and Antarctic regions. There is "exceptionally low" sea ice cover for the globe as a whole.
The graph above, based on the latest findings of the National Snow and Ice Data Centre (NSIDC), shows an alarming decline in global sea ice coverage for 2016; yet more evidence of a rapidly warming world.
The Arctic region set another record low extent last month, averaging 9.08 million sq km (3.51 million sq mi), which was 800,000 sq km (309,000 sq mi) below November 2006, the previous lowest November. Or put another way, it was roughly 1.95 million sq km (753,000 sq mi) below the 1981 to 2010 long-term average for November, equivalent to losing an area the size of Mexico. According to NSIDC, this was due to unusually high air temperatures, winds from the south and a warmer ocean. Some parts of the North Pole are now up to 20°C (36°F) above what they should be for this time of the year, underscoring the magnitude of heat increase.
Dr Friederike Otto, a senior researcher at Oxford's Environmental Change Institute, told BBC News that in pre-industrial times "a heatwave like this would have been extremely rare – we would expect it to occur about every 1,000 years." She added that scientists are "very confident" that the recent weather patterns were linked to anthropogenic climate change. "We have used several different climate modelling approaches and observations – and in all our methods, we find the same thing; we cannot model a heatwave like this without the anthropogenic signal."
A study published last month in the journal Science, by researchers including NSIDC's Julienne Stroeve, links Arctic sea ice loss to cumulative CO2 emissions in the atmosphere through a simple linear relationship. The paper examining this relationship is based on satellite and pre-satellite observations since 1953, and in climate models. The observed relationship is equivalent to a loss of 3 square metres (32 sq ft) for every ton of CO2 added to the atmosphere, compared to the average from all the climate models of 1.75 square metres (19 sq ft). This smaller value, or lower sensitivity, from the models is consistent with findings that the models tend to be generally conservative relative to observations in regard to how fast the Arctic has been losing ice cover.
As more and more white ice is lost, a feedback loop is created. Darker open waters mean a lower albedo (reflectivity). This in turn leads to increased solar heating in the Arctic Ocean and adjacent seas, which further accelerates melting and warming, and so on. If trends continue, the first ice-free summers in the Arctic will occur during the early 2020s, with year-round "blue ocean" events by 2040. This would be 60 years earlier than some previous climate models predicted and the first time in 100,000 years that the region has been ice-free, with major consequences for the Earth's climate systems.
The rapid changes in the Arctic are occurring in parallel with a similar decline in sea ice on the opposite side of the planet. For many years, a favourite argument for those denying the science of climate change has been that the Antarctic is gaining sea ice. However, this trend may be starting to reverse, as shown on the graph below. Sea ice coverage in the Antarctic reached its annual maximum extent on 31st August this year, much earlier than average, and has fallen rapidly since then. Last month, a new record low was set for November with 14.54 million sq km (5.61 million sq mi) – 1.0 million sq km (386,000 sq mi) below the previous record low extent in 1986 and 1.81 million sq km (699,000 sq mi) below the 1981 to 2010 average. The drop in average for November was more than twice as large as the previous record set in November 1986.
Antarctic ice extent last month was lower than average on both sides of the continent, particularly within the Indian Ocean and the western Ross Sea. Moreover, several very large polynyas (areas of open water within the ice pack) have opened in the eastern Weddell and along the Amundsen Sea and the Ross Sea coast. Air temperatures at the 925 mbar level were up to 4 degrees Celsius (7 degrees Fahrenheit) above average near the sea ice edge at the start of November, corresponding to the period of rapid sea ice decline.
Last month, a deep subsurface rift was reported to have appeared within the West Antarctic ice shelf, the first time such an event had been observed. Also of concern is the Larsen B ice shelf, which has already partially collapsed and is likely to undergo a final collapse before the end of this decade.
"There are some really crazy things going on," said Mark Serreze, director of NSIDC, in an interview with Reuters. He worries that "Antarctica is the sleeping elephant that is beginning to stir."
International efforts to address climate change have shown signs of progress during the last year or so. A global pact was agreed at the COP 21 summit – committing most nations to reducing carbon emissions for the first time (pending ratification) and calling for zero net greenhouse gas emissions to be reached in the second half of this century. Outgoing President Obama, in a joint agreement with Prime Minister of Canada Justin Trudeau, has this week enacted a permanent ban on Arctic oil and gas drilling. However, much of the hard work and progress achieved in recent years could now be threatened by incoming President Trump, who wants to make it a "priority" to slash environmental regulations, cancel all funding of UN climate change programs and to massively expand the production of coal, oil and gas in the United States.
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