Researchers at Oregon State University said they combined analyses of four major contributors to potential sea level rise into a collective estimate, and compared it with evidence of past sea-level responses to global temperature changes, to arrive at their conclusion.
The major contributors to sea-level rise on a global scale will be melting of glaciers, melting of the Greenland ice sheet, melting of the Antarctic ice sheet and expansion of the ocean itself as it warms, the researchers said.
Hundreds of simulations were run through computer models to calculate how the four areas would respond to warming, and the response was mostly linear, matching sea level rise to temperature increases, OSU paleoclimatologist Peter Clark said.
"The study did not seek to estimate how much the planet will warm, or how rapidly sea levels will rise," Clark explained. "Instead, we were trying to pin down the 'sea-level commitment' of global warming on a multi-millennial time scale. In other words, how much would sea levels rise over long periods of time for each degree the planet warms and holds that warmth?"
While sea-level rise in the past century has been dominated by the expansion of the ocean and melting of glaciers, the biggest contributions in the future may come from melting of the Greenland ice sheet, which could disappear entirely, the researchers said.
The Antarctic ice sheet will likely reach some kind of equilibrium with atmospheric temperatures and shrink significantly but not disappear, they said.
"Keep in mind that the sea level rise projected by these models of 2.3 meters (7.5 feet) per degree of warming (Celsius) is over thousands of years," Clark said. "If it warms a degree in the next two years, sea levels won't necessarily rise immediately. The Earth has to warm and hold that increased temperature over time."
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