Factbox: Arctic experts warn of higher sea level rise

Tue May 3, 2011 2:00pm BST

(Reuters) - World sea levels could rise by between 0.9 and 1.6 meters (2ft 11in to 5ft 3in) this century, stoked by accelerated climate change in the Arctic, a study showed on Tuesday.

The projection, by the Arctic Monitoring and Assessment Programme, is higher than most past estimates including a 2007 report by the Intergovernmental Panel on Climate Change (IPCC), the main U.N. scientific group.

Rising sea levels are a threat to cities from New York to Buenos Aires, coasts from the Netherlands to China and low-lying islands in the Pacific or Indian Oceans.

Following is a history of sea level rise and projections:

HISTORY - Sea levels rose about 120 meters (almost 400 ft) after a thaw at the end of the last Ice Age about 21,000 years ago released vast amounts of water frozen on land.

Sea levels stabilized about 2,000 to 3,000 years ago, with "no significant change from then until the late 19th century," the IPCC said in 2007. During the 20th century, they rose about 17 cm. Since 1993, rates have accelerated to about 3 mm per year.

RECENT ESTIMATES

May 2011 - "Global sea level is projected to rise by 0.9 to 1.6 meters by 2100 and the loss of ice from Arctic glaciers, ice caps and the Greenland ice sheet will make a substantial contribution," according to a report overseen by the AMAP, part of the eight-nation Arctic Council.

September 2009 - U.N. Secretary-General Ban Ki-moon said "by the end of this century, sea levels may rise between half a meter and two meters."

March 2009 - Sea-level rise may well exceed one meter by 2100, according to a group of leading scientists meeting in Copenhagen and updating IPCC findings from 2007.

February 2007 - The IPCC said sea levels could rise by between 18 and 59 cm by 2100. Another 10 to 20 cm could be added if flows of Greenland and West Antarctic ice accelerated in line with rising temperatures. It also said sea level rise would continue for centuries.

2001 - Sea levels could rise by between 9 and 88 cm by 2100, with a central estimate of 48 cm, according to the IPCC.

1995 - Sea levels could increase by between 13 and 94 cm by 2100, according to the IPCC.

1990 - The IPCC said seas could rise by between 31 and 110 cm under "business as usual policies" this century, i.e. without action to combat global warming.

SOURCES OF MELT

In 2007, the IPCC said the biggest contributor to sea level rise would be thermal expansion -- water increases in volume as it warms. It said thermal expansion would contribute about 70 to 75 percent to sea level rise this century.

Glaciers from the Andes to the Alps, ice caps and Greenland were also expected to contribute water. Most of Antarctica is too cold to melt and was expected to get more snow, meaning it will take water from the oceans, the IPCC said.

ICE SHEETS

Antarctica contains enough ice to raise sea levels by about 57 meters if it ever all melted. Worries include that a collapse of ice shelves around the coast may allow inland ice to slide faster toward the ocean. Greenland's ice would raise sea levels by 7 meters if it all vanished.

(Editing by Janet Lawrence)

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