Climate system modeling in the framework of the tolerable windows approach:: The ICLIPS climate model

The computational burden associated with applications of the Tolerable Windows Approach (TWA) considerably exceeds that of traditional integrated assessments of global climate change. As part of the ICLIPS (Integrated Assessment of Climate Protection Strategies) project, a computationally efficient climate model has been developed that can be included in integrated assessment models of any kind. The ICLIPS climate model (ICM) is implemented in GAMS. It is driven by anthropogenic emissions of CO2, CH4, N2O, halocarbons, S(F)6, and SO2. The output includes transient patterns of near-surface air temperature, total column-integrated cloud cover fraction, precipitation, humidity, and global mean sea-level rise. The carbon cycle module explicitly treats the nonlinear sea water carbon chemistry and the nonlinear CO2 fertilized biosphere uptake. Patterns of the impact-relevant climate variables are derived form empirical orthogonal function (EOF) analysis and scaled by the principal component of temperature change. The evolution of the latter is derived from a box-model-type differential analogue to its impulse response function convolution integral. We present a description of the ICM components and some results to demonstrate the model's applicability in the TWA setting.