The lack of information about future changes in extreme weather is a major constraint of Integrated Assessment Models (IAMs) of climate change. The generation of descriptions of future climate in current IAMs is assessed. We also review recent work on scenario development methods for weather extremes, focusing on those issues which are most relevant to the needs of IAMs. Finally, some options for implementing scenarios of weather extremes in IAMs are considered.Keywords: Integrated Assessment Models, climate change, scenarios, extreme weather events, general circulation models, regional climate models.
INTEGRATED ASSESSMENT AND CLIMATE CHANGEOne of the essential characteristics of integrated assessment is the simultaneous consideration of the multiple dimensions of environmental problems such as climate change. A number of formal integrated assessment models (IAMs) for climate change have been developed over the last decade, starting with the models IMAGE 1.0 and ESCAPE in the early 1990s [1,2]. These models were constructed using modules that are reduced-form versions of more complex models, for example of the climate system, the economy and ecosystems. Most climate modules in IAMs generate zero (i.e., globally-averaged; e.g., PAGE) or one (i.e., zonallyaveraged; e.g., IMAGE) dimensional descriptions of future climate, usually at a mean (e.g., 30-year average) seasonal or annual resolution [3][4][5]. Some IAMs (e.g., IMAGE 2.2 and AIM) then generate spatially explicit, i.e., two-dimensional, descriptions of future climate, usually by accessing stored patterns of climate change derived from more complex General Circulation Model (GCM) experiments [6][7][8].These approaches to generating future climate descriptions in IAMs, which are reviewed in Section 2, are computationally efficient and allow multiple experiments to be easily conducted in an integrated framework. The climate output is then input into an ecosystem, agriculture or health impacts module (e.g., AIM), or used directly to estimate the economic cost of climate damage from a lookup climate damage function (e.g., DICE). In either case, the current lack of any information about changes in daily or extreme weather (the focus of this review) is a major weakness. Agriculture, for example, is likely to be as, or more, sensitive to changes in daily weather sequences and the occurrence of extreme weather events than to changes in mean monthly or seasonal climate [9][10][11]. Potential changes in extremes and the ensuing changes in risk are also important for sectors such as water resources and insurance [12,13]. Climate damage functions that express the economic impact of climate change as a function of global-(or regional-) mean climate alone are likely to underestimate the economic damage associated with extreme events such as flooding and storms (e.g., in the UK, the October 1987 windstorm event is estimated to have cost insurers 3.1 billion US dollars, with further economic losses of 2.7 billion US dollars [14]). The lack of information about chan...