This section summarizes recent developments that are likely to affect the construction of scenarios over the coming few years. One of these developments is construction of the new SRES emission scenarios. Some features of these scenarios and their implications for atmospheric composition, global climate, and sea level are described below. In addition, a brief review of possible regional climate changes during the 21st century is presented, followed by discussions of stabilization scenarios and changes in climate variability and extreme eventskey issues in constructing scenarios for policy-relevant impact and adaptation assessments.
Development of the SRES scenarios (Nakicenovic et al., 2000) is outlined in Section 3.2.4.1. The 40 scenarios, 35 of which are fully quantified, are based on four different narrative storylines and associated scenario families. Each storyline describes a different world evolving through the 21st century, and each may lead to quite different GHG emissions trajectories. Four of the scenarios are designated as "markers," each characterizing one of four "scenario families"; two additional scenarios illustrate alternative energy developments in one of the families. The storylines and scenario families are as follows:
Measures of global population, economic development (expressed in annual GDP), and equity (per capita income ratio) for 2050 and 2100 that are implied under the SRES scenarios are shown in Table 3-9, alongside the IS92a scenario and estimates for the present day. Attempts are underway to "downscale" aspects of these global scenarios for use in regional impact assessment (e.g., Lorenzoni et al., 2000).
Table 3-10: Examples of impacts resulting from projected changes in extreme climate events. | |
Projected Changes during the 21 st Century in Extreme Climate Phenomena and their Likelihooda |
Representative Examples of Projected Impactsb (all high confidence of occurrence in some areasc) |
Simple Extremes | |
Higher maximum temperatures; more hot days and heat wavesd over nearly all land areas (Very Likelya) |
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Higher (increasing) minimum temperatures; fewer cold days, frost days, and cold wavesdover nearly all land areas (Very Likelya) |
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More intense precipitation events (Very Likelya over many areas) |
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Complex Extremes | |
Increased summer drying over most mid-latitude continental interiors and associated risk of drought (Likelya) |
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Increase in tropical cyclone peak wind intensities, mean and peak precipitation intensities (Likelya over some areas)e |
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Intensified droughts and floods associated with El Niño events in many different regions (Likelya) (see also under droughts and intense precipitation events) |
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Increased Asian summer monsoon precipitation variability (Likelya) |
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Increased intensity of mid-latitude storms (little agreement between current models)d |
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a Likelihood refers
to judgmental estimates of confidence used by TAR WGI: very likely (90-99%
chance); likely (66-90% chance). Unless otherwise stated, information on
climate phenomena is taken from the Summary for Policymakers,
TAR WGI. b These impacts can be lessened by appropriate response measures. c Based on information from chapters in this report; high confidence refers to probabilities between 67 and 95% as described in Footnote 6 of TAR WGII, Summary for Policymakers. d Information from TAR WGI, Technical Summary, Section F.5. e Changes in regional distribution of tropical cyclones are possible but have not been established. |
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