Assessment of the Remaining Carbon Budget: Incorporation of Nonlinear Feedbacks in a Simple Response Model

Abstract

Anthropogenic emission of greenhouse gases is causing an unbalance in the Earth’s climate system, leading to global climate change. The implications of these changes are dramatic, with a need for a global-scale assessment. The remaining carbon budget (RCB) is a measure of the amount of greenhouse gasses (GHGs) that can be emitted if we are to reach a specific temperature target. Traditionally, carbon budgets are assessed from experiments in Earth System Models (ESMs) or less complicated reduced complexity models, such as the Model of the Assessment of Greenhouse Gas Induced Climate Change (MAGICC). The large spread between ESMs implies that one would need to study an ensemble of models. An alternative approach, which so far has remained unexplored is to use simple response models to assess RCBs and to build in a non-linear effect framework explicitly.

The construction of a simple response model (SRM) and estimated likelihood plots for the RCB show that the SRM estimates are consistent with MAGICC. A non-linear forcing effect framework enables the implementation and study of non-linear Earth system feedbacks. The estimates use a combination of emulators of 14 ESMs from the Coupled Model Intercomparison Project 5 (CMIP5) ensemble, to even out the climate sensitivity of each model.