Does Half a Degree of Global Warming Matter? Results From the BRACE 1.5 Study

Systems Conversation with Brian O'Neill, National Center for Atmospheric Research

In 2015, 195 countries negotiated the Paris Agreement on climate change, which set long-term goals of limiting global mean warming to well below 2 C and possibly 1.5 C. This event stimulated substantial scientific interest in climate outcomes and impacts on society associated with those levels of warming. Recently, a project coordinated at NCAR was undertaken to produce new global climate model simulations of scenarios that stabilize warming at 1.5 and 2 C, and to investigate their potential impacts. The project, BRACE 1.5 (Benefits of Reduced Anthropogenic Climate changE), asks whether impacts differ substantially between the two climate scenarios, accounting for uncertainty in climate outcomes and in societal conditions. Impact assessment focuses on extreme climate events and the health, agricultural, and building energy sectors. Modeling approaches include the use of three different global, multi-region integrated assessment models (IAMs), both a process-based and an empirical crop model, and an epidemiological model of heat-related mortality. He discusses the BRACE 1.5 study design and key conclusions, and gives a more detailed account of an agricultural impact assessment linking an IAM to the NCAR climate model.