National attribution of climate damages under Earth system uncertainty

Abstract:

Understanding which nations are responsible for the impacts of climate change is essential to guiding the “common but differentiated responsibilities” framework that structures international climate negotiations and to informing climate impact loss and damage assessments. Existing national attribution analyses have focused on individual countries’ contribution to global mean temperature, rather than local or regional climate impacts. Furthermore, the few analyses that have extended national attribution to climate impacts have not explicitly simulated individual nations’ contributions, which can lead to an over- or under-estimation of national-level culpability in climate impacts. Here we apply a three-step framework to estimate the contribution of individual nations to the historical economic impacts of climate change while accounting for uncertainties at each step in the causal chain. First, we use a simple emissions-driven climate model to simulate individual nations’ contributions to global greenhouse gas concentrations; second, we use fully-coupled multi-model and single-model ensembles of the Earth system to derive relationships between GHG concentrations and country-level temperature change, allowing us to reconstruct local temperature trajectories attributable to individual nations; and lastly, we apply empirically derived relationships between temperature and growth to estimate the country-level damages associated with these temperature trajectories. Preliminary results indicate that total historical damages exceed 10% of GDP in many countries, with the United States responsible for around 25% of these damages and China responsible for around 10%. Model structure, internal variability, and the empirical shape of the “damage function” that relates temperature to GDP all generate uncertainties in these results. This work highlights the possibility of advancing “end-to-end” attribution work by integrating simple and complex climate models with econometric relationships, providing critical scientific insight for national accountability in a warming world.