Has Greenland's ice sheet reached a tipping point?

Yes

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by Kallie Szczepanski

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Greenland's ice sheet may well have already reached a "tipping point," a threshold beyond which loss of the entire sheet is inevitable, regardless of future changes that humans may make in their greenhouse gas emissions.

Most of us see global warming as a gradual, steady process. The atmosphere collects a small percentage of additional greenhouse gas each year, global average temperature rises by a few tenths of a degree, the weather gets a little bit stranger. This is the vision of global warming's course predicted by the 2007 U.N. Climate Panel report. According to the U.N., it will take centuries for the Greenland ice sheet to melt.

However, a joint British/German/U.S. report published in the Proceedings of the National Academy of Sciences journal on February 4, 2008 noted that in fact, the global climate tends to change in leaps and starts. Once a tipping point is reached, the climate shifts dramatically, and settles in to a new equilibrium. For example, the Younger Dryas cold snap involved a sudden 5 degree Celsius temperature drop that happened in less than a decade around 12,900 years ago, and lasted for about 1400 years. Climate researchers theorize that it was caused by and influx of fresh water from melting North American glaciers. (This is the effect dramatized in the movie "The Day After Tomorrow," though in reality it happened over several years, rather than several days.)

In the case of our current global warming "Society may be lulled into a false sense of security by smooth projections of global change," the scientists write in this report. As our climate undergoes increasing upheaval, it's likely to shift in fits and starts, reaching a tipping point and then lurching into a new relatively steady state.

So, what about Greenland's ice cap? Has it already reached a tipping point? Many scientists worry that it has. According to NASA satellite data, 552 billion tons of ice melted off of Greenland in 2007- 15% more than average, and more than any other year recorded. (Ominously, it broke a record made in 2005.) As receding glaciers leave bare rock exposed, and melt-water eats away at the remaining ice, Greenland's heating and melting is caught in a feedback spiral that will probably end with the entire ice cap disappearing by 2050, rather than 500 years from now. In fact, some models show it melting entirely by 2022; that would have catastrophic results.

What would a swift and complete melt-off mean for the rest of the world? There are two possible scenarios. First, the dense, cold, fresh melt-water could disrupt and stop the warm, salty Gulf Stream, causing it to stop (the previously noted "Day After Tomorrow" effect). This would cut off the transfer of heat from the tropics to eastern North America and Western Europe, triggering another Ice Age.

The second scenario is that the Gulf Stream would continue, and the Greenland melt-water would raise the global sea-level by 6 or 7 meters (18 to 21 feet). In that case, coastlines everywhere would disappear, drowning islands and inundating seaside cities around the world. In the U.S., Florida and Louisiana would be gone, along with every major coastal city: New York, Boston, Washington D.C., Philadelphia, Atlanta, Los Angeles, San Diego, Portland, and Seattle. Central Asia, the Amazon heartlands of Brazil and Venezuela, most of Argentina, Bangladesh, huge chunks of lowland China and Siberia, and even central Australia would be covered with seawater. Cuba would be just a series of unconnected mountain peaks poking their heads above the water.

This outcome sounds outlandish, ridiculous, but most of us could see it within our lifetimes. It may already be inevitable, given the ever-increasing melting now happening on Greenland. (This isn't even taking Antarctica into account... gulp.)

So what should we do? Just give up, build a boat, and buy some water-wings for the kids? Absolutely not. We need to make substantial cuts in our greenhouse gas emissions now, this year, not by 2015 or 2020. Governments are by their nature conservative (even the ones led by liberals), so the people of every country need to come together and demand change. Pester your leaders for cleaner energy, and reduce your own consumption, not only of fossil fuels, but also of "things." Remember, everything you buy had to get to your community somehow: by truck, ship, or airplane. Don't take unnecessary car-trips, and support local farmers or grow your own food. It's painful, it isn't what people want to hear, but we in the developed world need to completely revamp our lifestyle, and I mean *now*.

Oh, and I wouldn't buy any beach-front property, if I were you.

Sources:
"Arctic Sea Ice Gone in Summer Within Five Years?" Seth Borenstein, AP (Dec. 12, 2007). http://news.national geographic.com/news/ 2007/12/071212-AP-ar ctic-melt_2.html

"Glo bal warming and sea levels- Florida," Miami City Forum
http://www.city -data.com/forum/flor ida/54952-global-war ming-sea-levels-2.ht ml

"Tipping point' on horizon for Greenland ice," Alister Doyle, Scientific American (Feb. 4, 2008). http://www.sciam.com /article.cfm?id=tipp ing-point-on-horizon

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