Global Sea Level to Rise by Seven Feet for Every Degree of Sustained Global Warming

For every degree (Celsius) rise in the global temperature that sustained over a long period of time, the sea levels would rise about seven feet or 2.3 meters, according to a new study. The estimated rise, researchers said, will happen over many thousand years.

For the study, researchers looked at the impact of four major contributors to sea level rise in the future along with data from climate history. The major drivers of sea level rise are the melting ice-sheets in Antarctica and Greenland, thermal expansion of oceans and melting of glaciers. The ice sheets in Antarctica and Greenland alone hold about 99.5 per cent of the Earth's glacier ice.

"The study did not seek to estimate how much the planet will warm, or how rapidly sea levels will rise," noted Peter Clark, an Oregon State University paleoclimatologist and author of the study. "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?"

A recent study had shown that the ice-sheets at Greenland and Antarctica have been melting at a rate of 300 billion tons per year. However, researchers of this study said that the melting could be a result of natural changes instead of global warming.

"The simulations of future scenarios we ran from physical models were fairly consistent with evidence of sea-level rise from the past," Clark added in a news release. "Some 120,000 years ago, for example, it was 1-2 degrees warmer than it is now and sea levels were about five to nine meters higher. This is consistent with what our models say may happen in the future."

The current study was based on comparing climate conditions of the past and using computer simulations to understand how much the sea level is expected to rise in the future. Researchers used many climate models to see how the four areas are responding to rise in temperatures. They found that with the exception of the ice-sheet in Greenland, the ice melt and subsequent sea-level rise was proportional to rise in global temperatures.

"As the ice sheet in Greenland melts over thousands of years and becomes lower, the temperature will increase because of the elevation loss," Clark said. "For every 1,000 meters of elevation loss, it warms about six degrees (Celsius). That elevation loss would accelerate the melting of the Greenland ice sheet."

Ice-sheet loss in Antarctica happens mostly due to calving- when massive icebergs break and float away from the main glacier. Recently, an iceberg measuring 278 square miles (720 square kilometers), a size that's larger than the city of Chicago, broke off from Antarctica's Pine Island Glacier.

Researchers said that ice-sheet in Greenland may disappear completely in the future while the ice-sheet in Antarctica will reduce in size, but not disappear.

Clark added that the sea level rise will happen over a course of thousands of years as this kind of rise requires sustained warm temperature over a long period of time. However, the major greenhouse gas, carbon dioxide can stay in atmosphere for a long time, which could accelerate the sea level rise.

The study is published in the journal Proceedings of the National Academy of Sciences.