A simple climate assessment model has been developed to calculate changes in greenhouse gas (GHG) concentrations (in this case CO₂, CH₄, N₂O), resultant changes in radiative forcing, and changes in mean global surface temperature. Changes in atmospheric CO₂ concentrations resulting from prescribed emissions are calculated from an ocean and biosphere pulse response model. Changes in CH₄ and N₂O concentrations are calculated by integrating the differential equations describing their temporal evolution as a function of their emissions and atmospheric lifetimes. Past emissions for all three gases are taken from the EDGAR-HYDE data base while estimated future emissions are taken from the SRES S2 ASF scenario. The calculation of changes in radiative forcing from changes in GHG concentrations uses the formulae given in the IPCC third assessment report. Changes in radiative forcing from sulfate aerosol emissions are included. The temperature changes resulting from radiative forcing changes are calculated using an impulse response function determined from GCMs.

The model has been applied to assessing regional contributions to past and future anthropogenic climate change. This follows a proposal by Brazil during the Kyoto Protocol negotiations to link the relative contributions of Annex I Parties to emission reductions with the relative contributions of Parties to the global mean surface temperature increase. Emissions, concentration responses, radiative forcing responses, and surface temperature responses are partitioned across four global regions: 1) Canada + USA + OECD Europe + Oceania + Japan, 2) Eastern Europe and the former Soviet Union, 3) India + China + Southeast Asia, 4) Latin America + Africa + Middle East. Results for absolute and relative attribution of warming to regions are presented for several model runs based on different assessment scenarios and key issues regarding attribution in the presence of non-linear processes are discussed.