Global-scale climate impact functions: the relationship between climate forcing and impact

N W Arnell,T Osborn,P Zelazowski,S Brown,S N Gosling,J Hinkel,B Lloyd-Hughes,J A Lowe,R J Nicholls,C Huntingford

doi:10.1007/s10584-013-1034-7

Abstract

Although there is a strong policy interest in the impacts of climate change corresponding to different degrees of climate change, there is so far little consistent empirical evidence of the relationship between climate forcing and impact. This is because the vast majority of impact assessments use emissions-based scenarios with associated socio-economic assumptions, and it is not feasible to infer impacts at other temperature changes by interpolation. This paper presents an assessment of the global-scale impacts of climate change in 2050 corresponding to defined increases in global mean temperature, using spatially-explicit impacts models representing impacts in the water resources, river flooding, coastal, agriculture, ecosystem and built environment sectors. Pattern-scaling is used to construct climate scenarios associated with specific changes in global mean surface temperature, and a relationship between temperature and sea level used to construct sea level rise scenarios. Climate scenarios are constructed from 21 climate models to give an indication of the uncertainty between forcing and response. The analysis shows that there is considerable uncertainty in the impacts associated with a given increase in global mean temperature, due largely to uncertainty in the projected regional change in precipitation. This has important policy implications. There is evidence for some sectors of a non-linear relationship between global mean temperature change and impact, due to the changing relative importance of temperature and precipitation change. In the socio-economic sectors considered here, the relationships are reasonably consistent between socio-economic scenarios if impacts are expressed in proportional terms, but there can be large differences in absolute terms. There are a number of caveats with the approach, including the use of pattern-scaling to construct scenarios, the use of one impacts model per sector, and the sensitivity of the shape of the relationships between forcing and response to the definition of the impact indicator.

Highlights

There is a very strong policy interest in the impacts of climate change corresponding to different degrees of climate change
The characterisation of the relationship between global temperature change and impact was based on expert judgement, informed by ‘snapshot’ impact assessments made under different emissions and socio-economic scenarios
Piontek et al (2013) considered impacts related to water, agriculture, ecosystems, and malaria at different levels of global warming but their focus was on multi-sectoral overlaps, rather than the quantification of climate impact functions per se

Summary

Introduction

There is a very strong policy interest in the impacts of climate change corresponding to different degrees of climate change. Setting aside for the moment the challenges in defining, agreeing and delivering emissions pathways that achieve these targets, there is currently little systematic evidence on the impacts that would be incurred at different levels of change in global mean temperature. This is largely because the vast majority of impact assessments are concerned with estimating impacts at a particular time under specific emissions and socio-economic scenarios, rather than the impacts associated with a specific change in temperature. They observed that 11 % of the global population was subject to severe impacts in at least two of the four impact sectors at 4 °C

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Results

Conclusion