Model Ensembles
Across the globe there are many different climate models being developed. They differ in what physical laws governing the climate system that they describe and in its complexity. This means that all climate models will give different results. The size of these differences can be large or small depending on model, region, season, variable etc. Some models may perform well for a specific region/season/variable and some worse for other. So even though the climate models are advanced they are not a perfect description of the climate system.
A method to handle these uncertainties in the climate models is to use what researchers call ensembles. In ensembles, several climate models are used together, which enables estimations of how certain the results are. The spread can be significant, partly because models describe climatological processes in different ways. It is difficult to estimate the future climatic response and the correct answer will not show until the future occurs. The advantage of model ensembles is that if the same response is seen in several models the result is considered to be certain. If the responses are different in different models the result is considered to be less certain.
Scientist collaborate under different projects and programs. Two important and global programs are: Coupled Model Inter-comparison Project (CMIP) and Coordinated Regional Climate Downscaling experiment (CORDEX).
What is CMIP?
Coupled Model Inter-comparison Project is the standard experimental protocol for studying the output of coupled atmosphere-ocean general circulation models. CMIP provides a community-based infrastructure that supports climate model diagnosis, validation, inter-comparison, documentation and data access. This framework enables a diverse community of scientists to analyze the global models in a systematic fashion, a process which helps make models better. The international climate modelling community has participated in this project since it began in 1995.
What is CORDEX?
Coordinated Regional Climate Downscaling experiment (CORDEX) is responsible to advance and coordinate the science and application of regional climate downscaling models through global partnerships. The project office is hosted by SMHI since 2009.
Both CMIP and CORDEX are international collaborations between scientific institutions. They are also diagnostic model inter-comparison projects (model development). The programs also help evaluate how realistic the models are in simulating the recent past as well as provide projections of future climate change.
CMIP6 and CORDEX are endorsed by the World Climate Research Program (WCRP). Information from CMIP5 and CORDEX experiments are summarized in the Intergovernmental Panel on Climate Change (IPCC) reports, starting from the IPCC Fifth Assessment Report (IPCC AR5). CORDEX experiments are often used in regional assessment reports. There are some differences between the projects, such as resolution.
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