My question might sound bit silly. But, I am really curious to know what makes two GCMs differnt? We know, GCMs simulate past and future climate based on some assumptions. Regarding future, we can not comment anything, but when the task is to simulate past climate, why does the model output vary from each other? Can someone please elaborate on this with some examples?
Good question 1. the GCM formulation differs from each to another. 2. The physics represented within the GCMs differs from one GCM to another 3. The resolution (spatial resolution) sometimes differs from one GCM to another. I think I wrote about this in my Ph.D. thesis when I was describing the GCMs and their shortcoming in simulating regional climate. The thesis could be accessed online
Philbert Modest Luhunga Thank you very much Sir. I hope your thesis will give me good idea about the question I asked. Can you kindly provide me the online link for your thesis? And in partticular, which chapter from your thesis should I focus on to understand about GCMs and their underlying processes?
Hi, I tried to check the thesis there are a few pieces of information about the GCM. I advise you to google some books or papers on the topic. But all in all, you will find the same answers as indicated below.
1. The physics within the GCMs differs from one another. This means that parameterization schemes of small-scale processes such as convection, clouds, precipitations, atmospheric boundary layer height, fluxes of momentum, and heat differ from one GCM to another. You can try to google for instance "what are the parameterization schemes of the GCMs ICHEC-EC-EARTH (the GCM from Denmark meteorological institutes) and 1. MPI-M-MPI-ESM-LR (this is the GCM from the Swedish meteorological and hydrological institute. Or you can google "comparison between GCMs"
2. GCMs can differ in their resolution some GCMs have a resolution of 1000km by 1000km and some of them can have a spatial resolution of 100km to 100km (here you can google to find the resolution of GCMs from ECMWF and those from CMIP6) just to compare their spatial resolutions
3. The formulations of GCMs differ some of them use the Cartesian coordinates system other use the spherical coordinate system (but this will not affect their outputs), some GCMs are coupled with the ocean others are not coupled with the ocean (this could provide different results)
Thank you very much Sir for your kind reply. I will definately seach the aforementioned key words in google to learn more.
Search for and read "The Art and Science of Climate Model Tuning" in the Bulletin of the American Meteorological Society to gain an understanding of the complexity of forcing models to replicate some of the "essential" elements of the global climate
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