A new study published in Nature Communications investigates the risk of crossing planetary tipping points in climate scenarios that entail temporarily overshooting the Paris Agreement global warming temperature goals; that is, reaching a peak temperature above 1.5oC of global warming and subsequently stabilising at a lower target temperature. Most emissions trajectories that seek to stabilise the climate at 1.5oC or less entail overshooting, but the risk of a temporary overshoot triggering planetary tipping points is not well understood.
The consequences of climate tipping can include a global sea level rise of several metres, ecosystem collapse, widespread biodiversity loss and substantial shifts in global heat and rainfall patterns. The study examines the risks of temporary overshooting for four critical components of the Earth system with planetary-scale impacts, namely:
the Atlantic Meridional Overturning Circulation (think Gulf Stream): estimated tipping time of 15 – 300 years
the Amazon Rainforest: estimated tipping time of 50 – 200 years
the Greenland Ice Sheet: tipping time of 1,000 – 15,000 years
the West Antarctic Ice Sheet: tipping time of 500 – 13,000 years.
The study modelled 10 scenarios through to 2300, classified by peak overshoot temperatures (ranging from 1.53oC to 3.3oC) and subsequent stabilisation temperatures (ranging from 1.5oC down to pre-industrial levels). Under five of the scenarios, warming remained above 1.5oC in 2100 and tipping point risks were high. Scenarios that involved temperatures just 0.1oC above 1.5oC showed the lowest risk. Key findings are:
current policies and Nationally Determined Contributions are insufficient to minimise tipping risks, even if strong emission reductions after 2100 were to return temperatures to or below 1.5oC in the long term
tipping risk increases with every 0.1oC of overshoot peak temperature
scenarios that involved overshoot peak temperatures above 2.0oC entailed a non-linear acceleration of tipping risk.
The study concluded that to effectively limit tipping risks, holding warming well below 2oC at all times is essential, even in case of a temporary overshoot above 1.5oC, and in the long term, warming needs to return to less than 1oC above pre-industrial levels.
SOURCE: ON GOOD AUTHORITY 9th August (Climate Change Authority)