for National Geographic News
Greenland's massive ice sheet could begin to melt this century and may disappear completely within the next thousand years if global warming continues at its present rate.
According to a new climate change study, the melting of Greenland's ice sheet would raise the oceans by seven meters (23 feet), threatening to submerge cities located at sea level, from London to Los Angeles.
Even a partial melting of the ice sheet could have catastrophic consequences for low-lying countries like Bangladesh and the Maldives.
"A one-meter [three-foot] sea level rise would submerge a substantial amount of Bangladesh," Jonathan Gregory, the study's lead author and a climate scientist at the University of Reading in England, said in a telephone interview.
Scientists have previously calculated that if the annual average temperature in Greenland increases by almost 3° Celsius (5.4° Fahrenheit), its ice sheet will begin to melt.
Many experts believe the concentration of carbon dioxide in the atmosphere will have reached levels around the year 2100 that would cause the temperature to rise that much.
"We're not saying how long it will take to get to the three degrees or how long it will take to lose the ice sheet," Gregory said. "We're saying there's a high likelihood of passing this threshold of viability with the carbon dioxide levels that are currently being considered."
The research is described in this week's issue of the science journal Nature.
The issue of global warming is controversial. It's clear that, since the Industrial Revolution, atmospheric concentrations of carbon dioxide have increased 30 percent, enhancing the heat-trapping capability of the atmosphere.
Scientists generally believe that the combustion of fossil fuels to run cars, heat homes, and power factories is the primary source for this increase in carbon dioxide levels.
In the absence of emissions control policies, the United States Environmental Protection Agency says carbon dioxide concentrations will be 30 to 150 percent higher than the current 370 parts per million (ppm) found today.
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