Climate tipping points have been the subject of much debate and confusion. Now Professor Tim Lenton of the University of East Anglia has published a very good piece, "Tipping points in the Earth System," giving some intellectual substance to the notion.
Not surprisingly, the tipping point Prof. Lenton worries about most is the disintegration of Greenland's ice sheet. He told The Guardian:
We know that ice sheets in the last ice age collapsed faster than any current models can capture, so our models are known to be too sluggish.
His paper examines where Greenland's tipping point is:
Our present warming commitment alone seems insufficient to tip any of the elements we have identified. However, it could get us close to the threshold for irreversible melt of the Greenland ice sheet. If that threshold is at the nearest end of its estimated error range (1°C further global warming) then it will be nearly impossible to avoid by mitigation unless we are lucky and the climate sensitivity is at the bottom end of its uncertainty range (circa 1.6°C warming for a doubling of pre-industrial CO2). If the threshold is further away (we estimate an upper limit of 2°C global warming) then mitigation would still need to be extremely aggressive to avoid it. Given this, it seems prudent to design long-term adaptation strategies in anticipation of a progressive melt of the Greenland ice sheet. Critically there remains an argument for mitigation even when the threshold is passed because the rate of GIS melt and the corresponding contribution to sea level rise depends on how far the threshold is exceeded.
Based on current information all the other potential tipping elements [which include the destruction of the Amazon rain forest and the disintegration of the West Antarctic Ice Sheet] might be avoided by limiting global warming to 2°C above pre-industrial (although we cannot be sure).
And that is as good an argument for limiting total warming as you'll find.
This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.
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Comments
View as Flat
JMG Posted 10:49 am
18 Aug 2007
Save the world: Reduce greenhouse gas emissions 5% annually.
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Colin Wright Posted 7:48 pm
18 Aug 2007
Hansen:An ice sheet response time of centuries seems probable, and we cannot rule out large changes on decadal time-scales once wide-scale surface melt is underway.
Lenton:The timescale for the ice sheet to melt is at least 300 years and often given as roughly 1000 years.
Or on the West Antarctic Ice Sheet.
Hansen:
We find it implausible that BAU scenarios ... would permit a West Antarctic ice sheet of present size to survive even for a century.
Lenton:The West Antarctic Ice Sheet (WAIS) is thought to be less vulnerable to warming than the Greenland Ice Sheet but a threshold could still be accessed this century
I'm no expert, and there could be no real contradictions here between the authors. But there does at least seem to be a difference of emphasis. The albedo-flip picture could be a more important, more holistic way to look at the Earth than a series of tipping points.
Incidentally, I heard on the radio today that the Arctic ice cap extent is at its smallest size ever -- yet we still have at least another month of summer melting to go.
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Delay And Deny Posted 1:30 am
19 Aug 2007
I'll have to put that on my list of now cheap places to buy land for my summer home. Alberta Canada is a strong contender. Ideally, I'd figure out where the land ends under the ice in the Northwest Territories and have waterfront property for water skiing on the Arctic Ocean.
John Bailo
Sutext:
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dobermanmacleod Posted 4:11 pm
19 Aug 2007
Furthermore, as carbon sinks will become carbon emitters BIG TIME, it will also result in runaway global warming.
In my opinion, the IPCC severely underestimated the rate of ocean rise due to melting ice caps and glaciers, but still that will be a slow motion tipping point. Instead, we should be very concerned about the carrying capacity of the earth abruptly dropping in the next couple of decades.
There are historical examples of more mild abrupt climate changes, and they resulted in famine, war, pestilence, and death (the Four Horsemen). The difference is we now have a thousand times more people, and weapons of mass destruction.
Frankly, worrying about the ice caps and glaciers melting is rather naive, when the eco-systems that regulate the carbon budget are collapsing. This is just like the false assumption that mankind will be able to so drastically cut their emissions so fast as to be able to avoid either abrupt climate change or runaway global warming.
Unless you find a cost effective way to start removing the excess CO2 from the air soon, it is all over. The gigantic cost of completely rebuilding our energy infrastructure is predictably causing political gridlock. Developing countries will continue to rapidly increase their emissions to "catch up" with developed countries. Besides, nature will predictably reduce her ability to remove the CO2 from the air (a decline of 30% by 2030 has been forecast).
Yeah, go on believing that the tipping point to fear most is the rise of ocean levels-ha! One faulty paradigm after another...perhaps mankind is too stupid to be sparred the approaching bottleneck?
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MarkUK Posted 8:02 pm
19 Aug 2007
But they're not.
Let's not pretend we know exactly what is going to happen.
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