The global and regional impacts of climate change under Representative Concentration Pathway forcings and Shared Socioeconomic Pathway socioeconomic scenarios.

Abstract

This paper presents a multi-sectoral evaluation of the global and regional consequences of future climate change across indicators representing impacts on heat extremes, water resources, river and coastal flooding, droughts, agriculture and energy use. It estimates change in physical hazard and resource base under different rates of climate change, characterising the uncertainty in regional climate change with scenarios constructed from CMIP5 climate models. Socio-economic impacts are estimated for each combination of rate of climate change and socio-economic scenario. The analysis adopts a novel approach using relationships between level of warming and impact to rapidly estimate impacts under any climate forcing. At the global aggregate scale, all the consequences of climate change considered here are adverse: the frequencies of droughts, floods and heatwaves all increase, with large increases under the highest rates of warming. Under the highest forcing (RCP8.5), by 2100 the median estimate of the average annual likelihood of a major heatwave at a point is 97% (compared with 5% now). The median estimate of the proportion of time in hydrological drought is 27% (up from 7% now), but a high-end estimate is 36%. The median estimate of the average likelihood of the current 2% river flood is 7%, but the high-end estimate is over 11%. The socio-economic impacts of climate change are determined by socio-economic scenario. The paper presents projections of indicators at the regional scale, by climate and socio-economic scenario, and these can provide the basis for subsequent assessments. The range in estimated consequences of climate change can be very large, especially at the regional scale, partly due to uncertainty in future emissions and future socio-economic conditions, but also due to scientific uncertainty in how climate changes in response to future emissions. The relative importance of these three main sources of uncertainty varies between indicators. By 2100 for most indicators the range across socio-economic scenario is greater than the range across the forcing levels considered here. For the indicators dependent on temperature, the largest source of scientific uncertainty is in the estimated magnitude of equilibrium climate sensitivity, but for the indicators determined by precipitation change the largest source of scientific uncertainty is in the estimated spatial and seasonal pattern of changes in precipitation.