Outline of the Projections Chapter in AR4 WGI: with Reference to the Emissions Scenarios

The projections chapter for AR4 WG1 has solicited model results for two model inter-comparison exercises for the AR4. These model inter-comparisons will form a major part of the projections chapter. The first inter-comparison is for coupled atmosphere-ocean general circulation models (AOGCMs) and the second is for models of intermediate complexity (EMICs).The scenario runs requested for these inter-comparisons will be described. To compliment this work these runs will also be performed with a tuned simple climate model (SCM). This SCM will be used to extend the scope by assessing the climate response to additional scenarios. It is anticipated that these scenarios will include the full set of SRES scenarios comparable to what was done for the TAR. Radiative forcing, carbon cycle feedback and climate sensitivity together with their uncertainties will be based on assessments across the AR4. In addition, where possible a probabilistic approach will be used. Other pertinent emissions scenarios may also be run with the SCM and perhaps an EMIC model and it is hoped to obtain advice during this session as to which emission scenarios should used in addition to produce global mean temperature projections for the AR4