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Greenland's ice is melting, but it won't be a green land tomorrow

Greenland, that icy land that even the Vikings had trouble colonizing, plays a pretty crucial role when it comes to our planet's climate.

Approximately 125,000 years ago, Earth was 3 to 5 degrees Celsius warmer on average than it is today, and sea levels were 4 to 6 meters higher. The ice sheets covering Greenland's land mass have trapped a significant amount of the water that used to be in the sea, thereby lowering sea levels, Susan Solomon, senior scientist at the National Oceanic and Atmospheric Administration (and the co-chair of the latest report from the Intergovernmental Panel on Climate Change) told attendees at the American Association for the Advancement of Science taking place in San Francisco.

If the land ice on Greenland were to melt completely, the sea levels could rise six or seven meters again, but the current scientific models indicate it will take thousands of years. Both land and sea ice around Greenland are melting. (Sea ice is melting, but it doesn't raise sea levels because it's already in the water.)

"It would take centuries, if not millennia, to get a four to six meter rise" in sea levels, she said. Global temperatures would have to be raised by 1.9 to 4.6 degrees Celsius and be kept that way for several centuries, she added.

But could the melt accelerate, like some other indicators of global warming? "We just don't know," she added.

Solomon further explained that there is man-made and natural global warming. The Earth was warmer 125,000 years ago because the planet's orbit was different. The atmosphere that surrounds the Earth in its natural state also traps sunlight. Without the greenhouse effect exerted by the natural atmosphere, the average temperature on Earth would be about minus 18 degrees Celsius. "We'd all be frozen."

Instead, the real average temperature (minus human effects) is around 15 degrees Celsius. Industrialization and pollution have raised average global temperatures by about 0.75 degrees Celsius since 1860, she said. (Venus, which has an atmosphere that consists of 90 percent carbon dioxide, is 500 degrees Celsius warmer than it would be without the CO2 layer.)

"What we have done is enhance the greenhouse effect by adding an infrared absorber, namely CO2," she said.