Risk of multiple interacting tipping points should encourage rapid CO 2 emission reduction

Evidence suggests that several elements of the climate system could be tipped into a different state by global warming, causing irreversible economic damages. To address their policy implications, we incorporated five interacting climate tipping points into a stochastic-dynamic integrated assessment model, calibrating their likelihoods and interactions on results from an existing expert elicitation. Here we show that combining realistic assumptions about policymakers’ preferences under uncertainty, with the prospect of multiple future interacting climate tipping points, increases the present social cost of carbon in the model nearly eightfold from US$15 per tCO 2 to US$116 per tCO 2 . Furthermore, passing some tipping points increases the likelihood of other tipping points occurring to such an extent that it abruptly increases the social cost of carbon. The corresponding optimal policy involves an immediate, massive effort to control CO 2 emissions, which are stopped by mid-century, leading to climate stabilization at <1.5 °C above pre-industrial levels.