Glacier and Ice Sheet Melt
The melting of ice sheets and glaciers around the world is accelerating and contributing to rising sea levels. Melting in Greenland is particularly dramatic, with the record year of 2012 witnessing surface melt far in excess of any earlier year in the satellite record. For a few days that year, 97 percent of the entire ice sheet indicated surface melting. Antarctica too is vulnerable to global warming and is melting despite being the coldest place on Earth. Melting of the Antarctic ice sheet serves as a valuable climate indicator, as well as a potential source of dangerous sea level rise, and may accelerate if key ice shelves continue to be lost.
Real Time Data
Greenland ice sheet melt trends
The Greenland ice sheet and its 240 marine-terminating glaciers are among the largest bodies of fresh water on the planet. According to the IPCC, the average rate of ice sheet melt from the Greenland ice sheet has substantially increased from 34 gigatons a year over the period 1992 to 2001 to 215 gigatons a year over the period 2002 to 2011.
Recent trends show that Greenland’s melt is accelerating, even in parts of the ice sheet once thought to be stable. A large region in the northeast of the ice sheet was stable until 2003, then changed abruptly to melting at a rate of 10 gigatons per year. The melt rate is now 15 to 20 gigatons per year and rising.
The IPCC has found that the warming threshold for near-complete loss of the Greenland Ice Sheet is somewhere between 1.8 to 7.2°F (1 to 4°C), but the uncertainty is so great that a likely range cannot be established.
It is likely that during the last interglacial period, when the global mean temperature never exceeded 3.6°F (2°C) above recent pre-industrial conditions, the Greenland Ice Sheet contributed up to 10 feet to sea levels. Full melt would contribute sea level rise of about 23 feet.
Antarctic ice sheet melt trends
Since the 1930s, the upper 1,000m of the Southern Ocean that surrounds Antarctica has warmed significantly in conjunction with climate warming. Scientists estimate the subsurface water in the Southern Ocean may be warming faster than any other part of the ocean. Warmer ocean water has led to the recent acceleration of melt on the West Antarctic Ice Sheet.
According to the IPCC, the average rate of ice loss from the Antarctic ice sheet has “likely increased from 30 gigatons per year (Gt yr–1) over the period 1992–2001 to 147 Gt yr–1 over the period 2002 to 2011,” with losses mainly attributed to the northern Antarctic Peninsula and the Amundsen Sea sector of West Antarctica.
Ice sheet trends and tipping points
Ultimately, knowledge of the mechanisms controlling the rate of ice loss in Greenland and Antarctica is limited, making it difficult for scientists to narrow the range of expected future sea level rise. It is possible that the warming to date has already passed the tipping point that eventually leads to major losses from the Antarctic and Greenland Ice Sheets.