Sea levels may rise as much as 27 inches through 2100 as water temperatures rise, glaciers melt in the Andes and Himalayas, and ice sheets in Greenland and Antarctica shed water, European scientists said.
The new estimate exceeds a previous forecast of as much as 59 centimeters by the United Nations’ Intergovernmental Panel on Climate Change in 2007, which didn’t fully account for the effects of melting ice, researchers with the independent Ice2sea project of 24 institutions in Europe and Chile said today.
The study is aimed at giving greater clarity on UN predictions for the effects of climate change to guide policy makers. Envoys from more than 190 nations are working to draft a new climate-change treaty by 2015 that will come into effect in 2020 and bind all countries. Average sea levels already rose by about 17 centimeters last century, according to the UN panel.
"The changing climate of the earth is the main driver of ice-sheet and glacier change," David Vaughan, a professor at the British Antarctic Survey and coordinator of Ice2sea, told reporters in London today. "Changes in climate that we see today and over the next 10 years will have a long-term impact into the future in terms of sea-level rise."
Ice2sea, which has published more than 150 scientific papers since 2009, has submitted its key findings to the IPCC. The UN panel will publish later this year an initial report out of four planned in its first comprehensive assessment of climate science since it shared the 2007 Nobel Peace Prize with former U.S. Vice President Al Gore.
Ice2sea is publishing its report a day before an unrelated meeting in Kiruna, Sweden, of the six-country Arctic Council, which is considering resource-use and transport rules as the disappearance of ice widens access to the world’s northernmost ocean. Arctic sea-ice cover shrank to its lowest recorded level last year, opening up parts of the ocean to shipping and mineral exploration. Sea ice doesn’t add to sea-level increases when it melts because it already displaces water.
Ice2sea’s forecast includes a new estimate of 3.6 centimeters to 36.8 centimeters as the most likely range for the contribution of melting continental ice to higher sea levels, Vaughan said. At the upper limit, the Ice2sea scientists have arrived at 95 percent certainty that the effects won’t exceed 84 centimeters, he said.
The new forecast for the total increase in sea levels, with gains of 33 centimeters to 69 centimeters for the highest probability band, includes the thermal-expansion effect of water occupying more space as temperatures warm.
Due to the earth’s gravitational field, which varies around the planet, rising sea levels affect the tropics near the equator the most and areas closest to the ice polar regions the least, according to Ice2sea.
Higher sea levels also need to be considered alongside changes in ocean circulation when looking at possible effects on storm patterns, Ice2sea said. The group’s researchers predict that extreme storm surges may be as much as 1 meter (3.3 feet) higher than at present on some European coasts over the next 50 years.
Antarctica holds enough ice to raise sea levels by about 57 meters, though full melting isn’t likely for thousands of years, according to the UN. Greenland contains enough ice to raise sea levels by about 7 meters.
The IPCC said in 2007 that Greenland and Antarctica contributed a combined 0.42 millimeters a year to sea-level increases from 1993 through 2003. That’s just over half the 0.77-millimeter contribution from mountain glaciers and smaller ice caps, and a quarter of the 1.6-millimeter rise as a result of water expanding with warmer temperatures.
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