AVOID 1: The significance of the signal of the impacts of climate change over the near term

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AVOID 1: The significance of the signal of the impacts of climate change over the near term

December 3, 2012
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Most climate change impact assessments have focused on impacts in the middle of the 21st century or later. This study examines the potential impacts of underlying climate change to 2030, in order to identify the magnitude and location of the near-term consequences of climate change.

The magnitude of underlying climate change is large, relative to internally-generated climatic variability, in some regions even by 2000 and 2010 (although this impact has not necessarily been detected due to this year-to-year variability), particularly where impacts are driven by temperature change. Impacts are projected for many systems in many regions. One implication is that the 1961-1990 baseline commonly used in climate change impact assessments may not represent well the “current” climate to which systems are frequently adjusted, at least in terms of temperature.

By 2020, large parts of many regions – especially in Africa, south America and parts of Europe and the Middle East – experience significant reductions in runoff, and large proportions of water-stressed populations here are exposed to increased water resources stress. Higher temperatures mean that maize yields are reduced everywhere, by around 15% globally. Cooling demands are substantially higher in Europe – by over 50%. Improving standards of coastal protection mean that climate change has relatively little effect in 2020 on average annual number of people flooded in coastal floods, although coastal wetland loss exceeds 10% in north America and the Caribbean.

By 2030 significant reductions in runoff are seen over 50% of the area in many regions, and in some regions – particularly south, southeast and northeast Asia under HadCM3 – some significant increases in runoff are apparent. This means that whilst the number of waterstressed people exposed to increase stress increases, the numbers of water-stressed people with an apparent reduction in water stress increases more markedly over 2020. The increasing signal of rainfall change also means that there is a large change from 2020 to 2030 in the numbers of people and extent of cropland exposed to increased flood risk, and an increase in exposure to changes in drought frequency.

There is relatively little uncertainty in the magnitude and regional distribution of impacts determined by temperature change or sea level rise, but much greater uncertainty over the impacts which are also dependent in precipitation change. This uncertainty varies regionally, with the greatest uncertainties in parts of Africa, south and north east Asia and south America.