Modeling the non-CO2 contribution to climate change

Carbon dioxide (CO2) is the best-known and most important driver of climate change, but the climate also responds to other anthropogenic forcers that have different sources, mitigation potentials, atmospheric residence times, and climate change potential. These drivers include non-CO2 greenhouse gases, short-lived climate forcers such as aerosol and ozone precursors, and changes in the land surface. Smart targeting of these non-CO2 drivers, in combination with a serious and sustained attempt to reach net-zero CO2 emissions, could result in substantial avoided climate damages. Evaluating the climate effect of non-CO2 greenhouse gas emissions is not yet possible in most state-of-the-art climate models, though exciting developments are occurring. Simpler tools including reduced-complexity climate models and climate metrics are currently used to evaluate the climate impacts of non-CO2 drivers. This primer discusses strengths and weaknesses of these approaches and opportunities and outlook for future development.