Quantifying Climate Feedbacks from Abrupt Changes in High-Latitude Trace-Gas Emissions

The overall goal in this project is to quantify the potential for threshold changes in natural emission rates of trace gases, particularly methane and carbon dioxide, from pan-arctic terrestrial systems under the spectrum of anthropogenically forced climate warming, and the extent to which these emissions provide a strong feedback mechanism to global climate warming. Although ice-core evidence suggests that an arctic or boreal source was responsible for more than 30% of the large increase in global atmospheric methane (CH4) concentration during deglacial climate warming, specific sources of that CH4 are still debated. Nevertheless, these among other recent findings underscore that the fate of natural trace-gas emissions over boreal regions possesses a potent potential for abrupt changes in greenhouse gas emissions as well as a climate feedback to anthropogenic forcing. To address these issues, we propose to employ the MIT Integrated Global Systems Model (IGSM) in a series of experimental simulations. In addition to a flexible climate model that is capable of spanning the range of uncertainty in climate sensitivity, aerosol forcing, and ocean heat-uptake response, the IGSM includes a comprehensive depiction of the process-level biogeophysics and biogeochemistry which govern the terrestrial hydrologic and ecologic systems, as well as a description of the global socio-economic systems that determine anthropogenic emission scenarios — under various climate policies or lack thereof. Therefore, these simulations will be designed to investigate the fate of key trace-gas emissions, namely carbon and methane, under various policy/no-policy emission scenarios, in conjunction with the range of uncertainty in modeled climate sensitivity, aerosol, and ocean heat-uptake response. From these, we will be able to explore the response of the natural biogeophysical systems, such as the extent of permafrost degradation, to these forcings and climate changes, how these manifest into changes in trace-gas emissions, which ultimately result in potential feedbacks to the climate system's response.