CLIMATE-CHANGE SCENARIOS FOR THE ASSESSMENTS OF THE CLIMATE-CHANGE ONREGIONAL ECOSYSTEMS

This paper outlines the different methods which may be used for the co nstruction of regional climate change scenarios. The main focus of the paper is the construction of regional climate change scenarios from c limate change experiments carried out using General Circulation Models (GCMs). An introduction to some GCM climate change experiments highli ghts the difference between model types and experiments (e.g. equilibr ium or transient). The latest generation of climate change experiments have been performed using fully coupled ocean-atmosphere GCMs. These allow transient simulations of climate change to be performed with res pect to a given greenhouse gas forcing scenario. There are, however, a number of problems with these simulations which pose difficulties for the construction of climate change scenarios for use in climate chang e impacts assessment. The characteristics of the transient climate cha nge experiments which pose difficulties for the construction of climat e change scenarios are discussed. Three examples of these problems are : different climate change experiments use different greenhouse gas co ncentration scenarios; the ''cold-start'' problem which makes it hard to link future projections of climate change a given calendar year; an d the drift of the climate is noticeable in the control simulations. I n order to construct climate change scenarios for impacts assessment a method has therefore to be employed which addresses these problems. A t present the climate modelling and climate change impacts communities are somewhat polarised in their approach to spatial scales. Current G CMs model the climate at resolutions larger than 2.5 degrees x 3.75 de grees, while the majority of impacts assessment studies are undertaken at scales below 50 km (or 0.5 degrees). This paper concludes by addre ssing the problems in bringing together these two different modelling perspectives by presenting a number of regional climate change scenari os.