On the optimality of 2°C targets and a decomposition of uncertainty

Determining international climate mitigation response strategies is a complex task. Integrated Assessment Models support this process by analysing the interplay of the most relevant factors, including socio-economic developments, climate system uncertainty, damage estimates, mitigation costs and discount rates. Here, we develop a meta-model that disentangles the uncertainties of these factors using full literature ranges. This model allows comparing insights of the cost-minimising and cost-benefit modelling communities. Typically, mitigation scenarios focus on minimum-cost pathways achieving the Paris Agreement without accounting for damages; our analysis shows doing so could double the initial carbon price. In a full cost-benefit setting, we show that the optimal temperature target does not exceed 2.5 degrees C when considering medium damages and low discount rates, even with high mitigation costs. With low mitigation costs, optimal temperature change drops to 1.5 degrees C or less. The most important factor determining the optimal temperature is the damage function, accounting for 50% of the uncertainty. Determining attractive response strategies for international climate policy is a complex task. Here, the authors develop a meta-model that disentangles the main uncertainties using full literature ranges and use it to directly compare the insights of the cost-minimising and cost-benefit modelling communities.

Automated summary

Determining international climate mitigation response strategies is a complex task, with various factors to consider. By analyzing uncertainties, it is possible to better compare the insights of the cost-minimizing and cost-benefit modeling communities.