Abstract
The overall global-scale consequences of climate change are dependent on the distribution of impacts across regions, and there are multiple dimensions to these impacts. This paper presents a global assessment of the potential impacts of climate change across several sectors, using a harmonised set of impacts models forced by the same climate and socio-economic scenarios. Indicators of impact cover the water resources, river and coastal flooding, agriculture, natural environment and built environment sectors. Impacts are assessed under four SRES socio-economic and emissions scenarios, and the effects of uncertainty in the projected pattern of climate change are incorporated by constructing climate scenarios from 21 global climate models. There is considerable uncertainty in projected regional impacts across the climate model scenarios, and coherent assessments of impacts across sectors and regions therefore must be based on each model pattern separately; using ensemble means, for example, reduces variability between sectors and indicators. An example narrative assessment is presented in the paper. Under this narrative approximately 1 billion people would be exposed to increased water resources stress, around 450 million people exposed to increased river flooding, and 1.3 million extra people would be flooded in coastal floods each year. Crop productivity would fall in most regions, and residential energy demands would be reduced in most regions because reduced heating demands would offset higher cooling demands. Most of the global impacts on water stress and flooding would be in Asia, but the proportional impacts in the Middle East North Africa region would be larger. By 2050 there are emerging differences in impact between different emissions and socio-economic scenarios even though the changes in temperature and sea level are similar, and these differences are greater in 2080. However, for all the indicators, the range in projected impacts between different climate models is considerably greater than the range between emissions and socio-economic scenarios.
Highlights
The assessment reports of the Intergovernmental Panel on Climate Change (IPCC) review hundreds of studies into the potential impacts of climate change (e.g. IPCC 2007, 2014)
The distribution of impacts across space and between regions is as relevant as the global aggregate impact when assessing the global-scale impacts of climate change; the distribution of impacts is highlighted in IPCC reports as one of the five integrative ‘reasons for concern’ about climate change alongside aggregate impacts
These emissions and socio-economic futures are here represented by the A1b, A2, B1 and B2 SRES storylines (IPCC Intergovernmental Panel on Climate Change 2000)
Summary
By 2050, global average temperature under A1b emissions would be between 1.4 and 2.9 °C above the 1961-1990 mean, with an average increase across climate models of around 1.9 °C. Global average sea level would be 12 to 32 cm higher than over the period 1961-1990, with an average increase of 18 cm (note that changes in temperature under A1b are between changes under RCP6.0 and RCP8.5: IPCC 2013). The spatial patterns of changes in temperature, precipitation, sea level and other relevant climatic variables vary between climate models, so the projected potential impacts vary. This section first describes the potential impacts across the world and across sectors under one example plausible climate story, and assesses the uncertainty in impacts by region and sector
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