Improving Carbon Cycle Feedbacks in Simple Climate Models: Adding Wetland Methane to MAGICC

Simple climate models (SCMs) can emulate many of the trends and processes found in ESMs allowing for much faster runs, but among other trade-offs, they can be limited by what is already available in ESMs. In the case of natural methane emissions, there remains a high degree of uncertainty even among larger scale models over the next century and beyond, particularly in regards to wetlands. Many of the models which do exist show a strong linear relationship between global temperatures and methane emissions from wetlands. The simple climate model MAGICC, meanwhile, had previously not included a dynamic natural methane response. A linear model of wetlands methane as a function of global temperature was calibrated to output data from existing models and incorporated into MAGICC. This new version of MAGICC draws from a distribution of parameters in line with the wide spread of estimates available from existing models and informed by the available observational data. The C1, C2, C3, and C4 scenarios from AR6 were run through the new model, all experiencing a wider spread of projected temperatures. While many uncertainties remain in this simplified approach, this raises concerns about 2°C targets in these scenarios.