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.