TURN DO WN THE H E AT: C L IM AT E E X T RE ME S , R EGION A L IMPA C TS, A N D TH E C A SE FOR R ESILIENCE
Box 1.1 Definition of Warming Levels and Base Period in this Report This report and the previous Turn Down the Heat report referenced future global-warming levels against the pre-industrial period. A “2°C World” and a “4°C World” is defined as the increase in global-mean near-surface air temperature above pre-industrial climate by the end of the 21st century. This approach is customary in the international policy debate, including the UNFCCC, as well as in scientific assessments closely related to this debate, such as those produced by the IEA (World Energy Outlooks) and UNEP (UNEP Emissions Gap Reports). By contrast, IPCC’s Fourth Assessment Report expressed warming projections relative to an increase in the mean over the period 1980–1999, while the upcoming Fifth Assessment Report (AR5) uses 1986–2005 as a base period. Given observed warming from pre-industrial levels to 1986–2005 of about 0.7°C, all projections in AR5 would thus be around 0.7°C “lower” than those shown in this report for the same emission scenarios and impact levels. In other words a “4°C world” scenario in 2100 in this report would be a world 3.3°C warmer than 1986–2005 in the AR5. See further details in Appendix 1. In addition, while projections in this report often refer to projections around the year 2100, it is also common to refer to averages for the 20 years around 2090, as is often done in many impact assessments and in the IPCC. In this case a 4°C scenario in 2100 would be about a 3.5°C scenario above pre-industrial for the 2080–2099 period, given the projected rate of warming in such scenarios of 0.5°C/decade by the end of the century. This scenario would thus be only 2.8°C warmer than the 1986–2005 base period by the 2080–2099 period yet it would be identical with the “4°C world” scenario in this report. While different base and averaging periods are used to describe the climate changes resulting from the same underlying emissions scenarios, it is important to realize that the concentration of carbon dioxide and other greenhouse gases and aerosols in a given year or period are not changed, nor is the nature of the impacts described.
Box 1.2 Extreme Events 2012–2013 During the last year, extreme events have been witnessed across the globe. A particular high-temperature event at a particular place cannot be attributed one-on-one to anthropogenic climate change, but the likelihood of such events is projected to increase, in particular in the tropics where local year-to-year variations are smaller. Although below-average temperatures were recorded over Alaska and northern and eastern Australia, high temperatures occurred over North America, southern Europe, most of Asia, and parts of northern Africa. Across the United States, the number of broken temperature records in 2012 doubled compared to the August 2011 heat wave. Extremes in other climate variables can occur in tandem with heat events, such as the extreme drought accompanying this year’s heat wave in the US, which extended into northern Mexico. The drought in northern Brazil was the worst in 50 years. By contrast, countries in Africa, including Tanzania, Nigeria, Niger, and Chad, experienced severe flooding because of an unusually active African monsoon season. Devastating floods impacted Pakistan as well, with more than 5 million people and 400,000 hectares of crops estimated to have been affected. Even in some areas of above-average warming, early in the year several unusually cold spells were accompanied by heavy snowfall, including in northeast China and Mongolia. 2012 saw a record loss of Arctic sea ice. The year 2012 was also an active year for tropical cyclones, with Hurricane Sandy the most noteworthy because of the high number of lives lost and infrastructure damaged in the Caribbean and in the United States. Typhoon Sanba in East Asia was the strongest cyclone globally in 2012; it affected thousands of people in the Philippines, Japan, and the korean Peninsula. Australia saw a severe heat wave during the Australian summer, with record temperatures and associated severe bush fires followed by extreme rainfall and flooding. Records were continuously broken, with the hottest summer on record and the hottest seven consecutive days ever recorded in Australia. A recent report by the Australian Climate Commission (Australian Climate Comission 2013) attributes the severity and intensity of recorded temperatures and extreme events to anthropogenic climate change. However, no studies have been published attributing the other extreme events listed above to anthropogenic climate change.
and services offered by these ecosystems. The impacts of sea-level rise and changes in marine conditions, therefore, are the focus for South East Asia, with the Philippines and Vietnam serving as examples for maritime and mainland regions respectively. • In South Asia, populations rely on seasonal monsoon rainfall to meet a variety of needs, including human consumption and irrigation. Agricultural production, an income source for approximately 70 percent of the population, in most part 2
depends on groundwater resources being replenished by monsoon rains. Snow and glacial melt in the mountain ranges are the primary source of upstream freshwater for many river basins and play an important role in providing freshwater for the region. The variability of monsoon rainfall is expected to increase and the supply of water from melting mountain glaciers is expected to decline in the long term. South Asia is, therefore, particularly vulnerable to impacts on freshwater resources and their consequences.