If Sudden Cooling Came, Arctic Sea Ice Would Recover In Years; Ice-Depleted Greenland In Centuries

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If the Arctic suddenly cooled, sea ice would recover within a few years. If the great ice sheets of Greenland and Antarctica lose enough ice to raise sea level a metre or more, though, it would take thousands of years for snowfall to build up the ice sheets again. The risk is real: we know that the West Antarctic ice sheet has collapsed many times in the past, raising sea levels at least 3 metres.

We can identify many other such dangerous "tipping points". The Amazon could flip from being rainforest to grassland, just as the Sahara suddenly dried up 8000 years ago. Massive amounts of methane could be released from undersea methane hydrates.

Even without tipping points, there is enormous inertia in the climate system. It takes decades for even the most immediate result of higher greenhouse gas levels - a rise in surface temperatures - to become apparent. It takes centuries longer for some effects to kick in fully, such as the oceans becoming poorer in oxygen as they slowly warm. These effects are essentially irreversible on a human timescale. Others, such as species going extinct and great cities being lost to the seas, are not reversible at all. The danger is that by the time we realise we are about to pass tipping points, it may be too late to do anything about it.

EDIT

http://www.newscientist.com/article/mg21228352.700-climate-unknown-if-and-when-tipping-points-will-come.html