Box 1.1 Anthropogenic climate change
The presence of so-called ‘greenhouse gases’ (e.g. carbon dioxide, methane, oxides of nitrogen and ozone) in the atmosphere retains heat and thus keeps the Earth’s temperature higher than it would otherwise be. They all occur naturally, but their atmospheric concentrations have been altered significantly by human activity. Industrial processes also create other greenhouse gases, not previously present in the atmosphere, and their concentrations are increasing as well. The global annual emission of carbon dioxide from burning fossil fuel and other industrial processes is estimated to have increased from about 0.1 Gigatonnes of carbon (GtC) in 1860 to almost 10 GtC by the end of the 20th century. Over the same period, the atmospheric concentration of carbon dioxide has increased from about 280 parts per million by volume (ppmv) to about 369 ppmv and the global temperature of the Earth has increased by about 0.6° C. The most recent assessment of the Intergovernmental Panel on Climate Change (IPCC, 2001) is that, globally averaged, the surface temperature of the Earth is going to increase by between 1.4°C and 5.8°C over the period 1990 to 2100 as a result of human activities. Over the same period, an associated rise in global mean sea level of between 9 and 88 cm is projected. The 1992 United Nations Framework Convention on Climate Change (UNFCCC), including its Kyoto Protocol, is aimed at stabilizing human-induced greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous interference with the climate system.
Figure 1.3 Variations of the Earth’s surface temperature over the last 140 years and the last millennium (IPCC, 2001)
month (e.g., a season, a year, a decade, 30 years, and so on). Climate variability can be defined as the range of values that the climate at a particular location can take over time. As explained already, climate variability is an inherent feature of the natural climate system. However, we recognise that climate variability and climatic extremes may get exacerbated as a result of global warming (IPCC, 2001).
fold between the 1950s and 1990s. These losses largely reflect an increase in the vulnerability of society as a whole to extreme events (Kunkel et al., 1999). In many cases this increased vulnerability has not been matched by an appropriate increase in adaptive capacity. Part of the observed upward trend in losses is linked to socioeconomic factors, such as population growth, expansion into and population concentration in flood prone areas, increasing wealth, as well as land use and river channel changes. However, these factors alone cannot explain the observed growth in economic losses; part of the losses can be linked to climatic factors, such as more intense storms, floods and droughts.
The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods. In this report, we adopt the UNFCCC approach and restrict our use of the term climate change to projected future conditions of climate under various greenhouse gas emission scenarios (see section 1.5).
The World Bank’s Water Resources Sector Strategy quotes examples of impacts of climate variability on economic performance. The drought in Zimbabwe in the early 1990s was associated with an 11% decline in GDP; the floods of 1999 in Mozambique led to a 23% reduction in GDP, and a drought in Brazil in 2000 halved projected economic growth. The scale of these losses highlights the need for water planners and managers to have a better understanding of the mechanisms of climate variability and their relationships with hydrological extremes such as floods and droughts.
1.3
Climate variability: phenomena and consequences 1.3.1. The Importance of climate extremes Extreme weather and climate events have received increased attention over the past decade, largely as a result of the exponentially-increasing losses that have been associated with them (Figure 1.4). Yearly economic losses from large events have increased ten-
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