Investigating 25 years of coupled climate modeling

The Coupled Model Intercomparison Project (CMIP) is an effort to compare model simulations of the climate system and its changes. In the quarter of a century since CMIP1 models have increased considerably in complexity and improved in how well they are able to represent historical climate compared to observations. Other aspects, such as the projected changes we have to expect in a warming climate, have remained remarkably stable. Here we track the evolution of climate models based on their output and discuss it in the context of 25 years of model development. 

We draw on temperature and precipitation data from CMIP1 to CMIP6 and calculate consistent metrics of model performance, inter-dependence, and consistency across multiple generations of CMIP. We find clear progress in model performance that can be related to increased resolution among other things. Our results also show that the models’ development history can be tracked using their output fields with models sharing parts of their source code or common ancestors grouped together in a clustering approach.

The global distribution of projected temperature and precipitation change and its robustness across different models is also investigated. Despite the considerable increase in model complexity across the CMIP generations driven, for example, by the inclusion of additional model components and the increase in model resolutions by several orders of magnitude, the overall structure of simulated changes remains stable, illustrating the remarkable skill of early coupled models.