Quantifying risks avoided by limiting global warming to 1.5 or 2°C above pre-industrial levels.

Abstract

The Paris Agreement aims to constrain global warming to ‘well below 2°C’ and to ‘pursue efforts’ to limit it to 1.5°C above pre-industrial levels. We quantify global and regional risk-related metrics associated with these levels of warming that capture climate-change related changes in exposure to water scarcity and heat stress, vectorborne disease, coastal and fluvial flooding; and project impacts on agriculture and the economy, allowing for uncertainties in regional climate projection. Risk-related metrics associated with 2°C warming, depending on sector, are reduced by 10 - 44% globally if warming is further reduced to 1.5°C. Comparing with a baseline in which warming of 3.66°C occurs by 2100, constraining warming to 1.5°C reduces these risks globally by 32- 85% and constraining warming to 2°C reduces them by 26 - 74%. In percentage terms, avoided exposure is highest for fluvial flooding, drought, and heat stress, but in absolute terms risk reduction is greatest for drought. Although water stress decreases in some regions, it is often accompanied by additional exposure to flooding. The magnitude of the percentage of damage avoided is similar to that calculated for avoided global economic damages associated with these same climate change scenarios. We also identify West Africa, India and N America as hotspots of climate change risk in the future.