The risky middle of the road – probabilities of triggering climate tipping points and how they increase due to tipping points within the Earth’s carbon cycle
Abstract. We investigate the probabilities of triggering climate tipping points under various shared socioeconomic pathways (SSPs), and how they are altered by including the additional carbon emissions that could arise from tipping points within the Earth's carbon cycle. Crossing of a climate tipping point at a threshold level of global mean surface temperature (threshold temperature), would commit the affected subsystem of the Earth to abrupt and largely irreversible changes with negative impacts on human well-being. However, it remains unclear which tipping points would be triggered under the different SSPs, due to uncertainties in the climate sensitivity to anthropogenic greenhouse gas emissions, the threshold temperatures of climate tipping points, and the response of tipping points within the Earth's carbon cycle to global warming. We include those uncertainties in our analysis to derive probabilities of triggering for 16 previously-identified climate tipping points within the Earth system. To conduct our analysis, we use the intermediate complexity climate model FaIR which is coupled to a conceptual model of the tipping processes within the Amazon rainforest and permafrost, which are the two major tipping elements within the Earth's carbon cycle. Uncertainties are propagated by employing a Monte Carlo approach for the construction of large model ensembles. We find that intermediate emission scenarios like SSP2-4.5 are highly unsafe with regard to triggering climate tipping points, with an average probability of triggering until the year 2500 of 65 %. Furthermore, the highest long-term temperature increase among all SSPs caused by carbon emissions from the Amazon and permafrost becomes possible under this scenario with 0.16 °C (0.03–0.91 °C) in 2500, which increases the average probability of triggering tipping points by 3.3 percent points (pp). This is due to the fact that maximum carbon emissions from tipping of the Amazon and permafrost become possible under this scenario, and they cause most warming when cumulative anthropogenic emissions are lower due to the saturating response of radiative forcing to increasing greenhouse gas concentrations. The risk of triggering climate tipping points is reduced significantly under SSP1-2.6 and even more so under SSP1-1.9, with average probabilities of triggering of 38 % and 28 % respectively, which are increased by 2.3 pp and 1.1 pp due to carbon emissions from the Amazon and permafrost.
Status: final response (author comments only)
Ensemble Outputs and Triggering Probabilities https://doi.org/10.5281/zenodo.8099908
Model code and software
Model Code and Evaluation Scripts (Version 1.1) https://doi.org/10.5281/zenodo.8121160
Viewed (geographical distribution)