3.6. How can We Improve Scenarios and their Use?

Some features of scenario development and application that are now well established and tested include continued development of global and regional databases for defining baseline conditions, widespread use of incremental scenarios to explore system sensitivity prior to application of model-based scenarios, improved availability and wider application of estimates of long-term mean global changes on the basis of projections produced by specialized international organizations or the use of simple models, and a growing volume of accessible information that enables construction of regional scenarios for some aspects of global change. [3.9.1]

There also are numerous shortcomings of current scenario development, many of which are being actively investigated. These investigations include efforts to properly represent socioeconomic, land-use, and environmental changes in scenarios; to obtain scenarios at higher resolution (in time and space); and to incorporate changes in variability as well as mean conditions in scenarios. Increasing attention is required on construction of scenarios that address policy-related issues such as stabilization of GHG concentrations or adaptation, as well as improving the representation of uncertainties in projections, possibly within a risk assessment framework. [3.9.2]

Table TS-2: Examples of impacts resulting from projected changes in extreme climate events.
Projected Changes during the 21st 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)	Increased incidence of death and serious illness in older age groups and urban poor Increased heat stress in livestock and wildlife Shift in tourist destinations Increased risk of damage to a number of crops Increased electric cooling demand and reduced energy supply reliability
Higher (increasing) minimum temperatures; fewer cold days, frost days, and cold wavesd over nearly all land areas (Very Likelya)	Decreased cold-related human morbidity and mortality Decreased risk of damage to a number of crops, and increased risk to others Extended range and activity of some pest and disease vectors Reduced heating energy demand
More intense precipitation events (Very Likelya over many areas)	Increased flood, landslide, avalanche, and mudslide damage Increased soil erosion Increased flood runoff could increase recharge of some floodplain aquifers Increased pressure on government and private flood insurance systems and disaster relief
Complex Extremes
Increased summer drying over most mid-latitude continental interiors and associated risk of drought (Likelya)
Increase in tropical cyclone peak wind intensities, mean and peak precipitation intensities (Likelya over some areas)e	Decreased crop yields Increased damage to building foundations caused by ground shrinkage Decreased water resource quantity and quality Increased risk of forest fire
Intensified droughts and floods associated with El Niño events in many different regions (Likelya) (see also under droughts and intense precipitation events)	Decreased agricultural and rangeland productivity in drought- and flood-prone regions Decreased hydro-power potential in drought-prone regions
Increased Asian summer monsoon precipitation variability (Likelya)	Increased flood and drought magnitude and damages in temperate and tropical Asia
Increased intensity of mid-latitude storms (little agreement between current models)d	Increased risks to human life and health Increased property and infrastructure losses Increased damage to coastal ecosystems
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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