Climate Change 2001:
Synthesis Report
Other reports in this collection
Figure 3-3:The background shows the annual mean change of rainfall (color shading) for (a) the SRES scenario A2 and (b) the SRES scenario B2. Both SRES scenarios show the period 2071 to 2100 relative to the period 1961 to 1990, and were performed by AOGCMs. Scenarios A2 and B2 are shown as no AOGCM runs were available for the other SRES scenarios. The boxes show an analysis of inter-model consistency in regional precipitation change. Regions are classified as showing either agreement on increase with an average change of greater than 20% ( large increase), agreement on increase with an average change between 5 and 20% ( small increase), agreement on a change between -5 and +5% or agreement with an average change between -5 and +5% ( no change), agreement on decrease with an average change between -5 and -20% ( small decrease), agreement on decrease with an average change of more than -20% ( large decrease), or disagreement ( inconsistent sign). A consistent result from at least seven of the nine models is defined as being necessary for agreement.
WGI TAR Box 10.1 (Figure 2)
3.15 Projected climate change will have beneficial and adverse environmental and socio-economic effects, but the larger the changes and rate of change in climate, the more the adverse effects predominate.

3.16 The impacts of climate change will be more severe the greater the cumulative emissions of greenhouse gases (medium confidence). Climate change can have beneficial as well as adverse effects, but adverse effects are projected to predominate for much of the world. The various effects of climate change pose risks that increase with global mean temperature. Many of these risks have been organized into five reasons for concern: threats to endangered species and unique systems, damages from extreme climate events, effects that fall most heavily on developing countries and the poor within countries, global aggregate impacts, and large-scale high-impact events (see Box 3-2 and Figure 3-1). The effects of climate change on human health, ecosystems, food production, water resources, small islands and low-lying coastal regions, and aggregate market activities are summarized below. However, note that future changes in the frequency or intensity of extreme events have not been taken into account in most of these studies (see also Question 4).

WGII TAR Sections 1.2, 19.3, 19.5, & 19.8
Box 3-2 Concerns about the risks from climate change rise with temperature.
  • Unique and threatened systems: Some changes in species and systems have already been associated with observed changes in climate, and some highly vulnerable species and systems may be at risk of damage or even loss for very small changes in climate. Greater warming would intensify the risks to these species and systems, and place additional ones at risk.
  • Extreme climate events: Increased frequencies and intensities of some extreme events have already been observed (see Question 2) and are likely to increase with further warming, as would the risks to human life, property, crops, livestock, and ecosystems. These risks increase where development is occurring in inherently dynamic and unstable zones (e.g., river floodplains and low-lying coastal regions) (see also Question 4).
  • Uneven distribution of impacts: In general, developing countries are at greater risk of adverse impacts from climate change than are developed countries, of which some of the latter may experience market sector benefits for warming less than a few °C. For greater warming, most regions are at risk of predominantly negative effects from climate change. But developing countries generally would continue to be more severely impacted than developed countries. Within countries, ulnerability varies and the poorest populations often have higher exposure to impacts that threaten their lives and livelihoods.
  • Global aggregate impacts: Globally aggregated market sector impacts may be positive or negative up to a few °C, though the majority of people may be negatively affected. With greater warming, the risk of negative global market sector impacts increases, and impacts would be predominantly negative for most people.
  • Large-scale, high-impact events: The probability of large-scale, high-impact events within a 100- year time horizon such as shutdown of the thermohaline circulation or collapse of the West Antarctic ice sheet is very low for warming less than a few °C. The risk, which is a product of the probabilities of these events and the magnitude of their consequences, is largely unquantified. For greater warming, and over a time horizon longer than 100 years, the probabilities and the risks increase, but by an amount that cannot now be estimated. See also Question 4.
WGII TAR Sections 5.2, 5.4, & 19.3
WGII TAR Sections 15.2 & 19.6
WGII TAR Section 19.4

WGII TAR Section 19.5

WGII TAR Section 19.6

Other reports in this collection