Key dangers largely left out of the IPCC special report on 1.5C of warming are raising alarm among some scientists who fear we may have underestimated the impacts of humans on the Earth’s climate.
The IPCC report sets out the world’s current knowledge of the impacts of 1.5C of warming and clearly shows the dangers of breaching such a limit. However, many scientists are increasingly worried about factors about which we know much less.
These “known unknowns” of #climate change are tipping points, or feedback mechanisms within the climate system – thresholds that, if passed, could send the Earth into a spiral of runaway climate change.
Tipping points merit only a few mentions in the IPCC report. Durwood Zaelke, founder of the Institute for Governance and Sustainable Development, said: “The IPCC report fails to focus on the weakest link in the climate chain: the self-reinforcing feedbacks which, if allowed to continue, will accelerate warming and risk cascading climate tipping points and runaway warming.”
He pointed to water vapour in the air, which traps heat in the atmosphere, as well as the loss of polar ice, the collapse of permafrost, and the migration of tropical clouds towards the poles.
Ice melting at the poles is known to be of particular danger. The Earth’s ice caps act as reflectors, sending some of the sun’s rays back into space and cooling the planet. When sea ice melts, it reveals dark water underneath, which absorbs more heat and in turn triggers greater warming, in a constant feedback loop.
Ice on land, such as in Greenland and under much of the Antarctic, may contain yet another feedback loop; when the ice melts, water percolates to the land below where it lubricates the slide of ice over rock and could accelerate the collapse of glaciers into the surrounding sea.
Bob Ward, of the Grantham Institute, said: “The IPCC summary for policymakers only mentions the west Antarctica and Greenland tipping points, which we may already have reached.”
The full report of the IPCC reflects our lack of knowledge of the full potential of tipping points, he said: “The underlying report suggests that the other tipping points are too poorly understood, or not likely to be triggered until higher amounts of warming – but given their consequences, one would expect a more risk-based approach. That is, you don’t ignore them until you know them to be impossible.”