Stochastic integrated assessment of climate tipping points indicates the need for strict climate policy

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this record Perhaps the most 'dangerous'aspect of future climate change is the possibility that human activities will push parts of the climate system past tipping points, leading to irreversible impacts. The likelihood of such large-scale singular events is expected to increase with global warming, but is fundamentally uncertain. A key question is how should the uncertainty surrounding tipping events affect climate policy? We address this using a stochastic integrated assessment model, based on the widely used deterministic DICE model. The temperature-dependent likelihood of tipping is calibrated using expert opinions, which we find to be internally consistent. The irreversible impacts of tipping events are assumed to accumulate steadily over time (rather than instantaneously), consistent with scientific understanding. Even with conservative assumptions about the rate and impacts of a stochastic tipping event, today's optimal carbon tax is increased by 1/450%. For a plausibly rapid, high-impact tipping event, today's optimal carbon tax is increased by >200%. The additional carbon tax to delay climate tipping grows at only about half the rate of the baseline carbon tax. This implies that the effective discount rate for the costs of stochastic climate tipping is much lower than the discount rate for deterministic climate damages. Our results support recent suggestions that the costs of carbon emission used to inform policy are being underestimated, and that uncertain future climate damages should be discounted at a low rate.NSFZüricher UniversitätsvereinUniversity of ZurichEcosciencia FoundationRoyal SocietyEuropean Commissio

Economics of tipping the climate dominoes

Greenhouse gas emissions can trigger irreversible regime shifts in the climate system, known as tipping points. Multiple tipping points affect each other's probability of occurrence, potentially causing a 'domino effect'. We analyse climate policy in the presence of a potential domino effect. We incorporate three different tipping points occurring at unknown thresholds into an integrated climate-economy model. The optimal emission policy considers all possible thresholds and the resulting interactions between tipping points, economic activity, and policy responses into the indefinite future. We quantify the cost of delaying optimal emission controls in the presence of uncertain tipping points and also the benefit of detecting when individual tipping points have been triggered. We show that the presence of these tipping points nearly doubles today's optimal carbon tax and reduces peak warming along the optimal path by approximately 1 degrees C. The presence of these tipping points increases the cost of delaying optimal policy until mid-century by nearly 150%.C.P.T. gratefully acknowledges support by the National Science Foundation through the Network for Sustainable Climate Risk Management GEO-1240507.Published online 18 January 2016. 6 month embargo.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Risk of multiple interacting tipping points should encourage rapid CO2 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 policymaker’s preferences under uncertainty, with the prospect of multiple future interacting climate tipping points, increases the present social cost of carbon (SCC) in the model nearly 8-fold from $15/tCO2 to$116/tCO2. 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 CO2 emissions, which are stopped by mid-century, leading to climate stabilization at <1.5 °C warming above pre-industrial levels