What is the accepted methodology to predict future climatic extremes using the results of climate models?
I have recently read a report about climatic extremes considering climate change (MICE, 2002). The report says that researchers fitted extreme value distributions (generalized extreme value, generalized Pareto) to the intensity of predicted, future climatic actions, e.g. rain, snow, wind. Applying these models, events with a large return period are used to assess the impact of climate change. Additionally, there is a recent Nature article by O’Gorman which also deals with future extreme events, particularly snow.
Considering that the predictions (projections per scenarios) can be made only in probabilistic terms. I would like to know how these predictions are made, what methodology are they using? I mean the actual climatic data, not the extreme value (statistical) analysis of them. For extreme value analysis, annual or more frequent maxima can/could be used. It is quite dubious that climate models would predict monthly or annual maxima of rain/snow for a certain region, up to the end of this century (or are climate models so sophisticated?). Someone told me that on this site (Earth System Grid Federation) there is an example of daily predicted snow data (this can be downloaded).
So, my main question is how this data, these predictions, are produced. What are the underlying assumptions of the models? Can these 100-year long simulations be used to predict extreme events within a 100 to 1000 year return period (these are common in engineering practice).
As far as I know, the climate models contain 'accurate' models (where the phenomenon is described by differential equations) and 'approximate' models (where empirical models are used). I guess the actual amount of precipitation for a given region belongs to the latter; in this case how uncertain are these models? (Surely the 'accurate' models have large uncertainty as well, but perhaps less).
I have an engineering background and I am interested in the effect of extreme climatic events on the reliability of structures; especially considering climate change. In order to study this, it would be great to know how reliable are the climate predictions regarding extreme events. If the probability distribution (or more complex probabilistic model of the actions) is given, the reliability of a structure (system) can be directly calculated. However, I am quite suspicious about the extremes predicted by the climate models.
It is quite hard to navigate through the thousand pages reports and find the probably one page long section which would answer my question. I would highly appreciate if someone could explain the main aspects of methodology, basic assumptions or point me to specific references, any help regarding the original question is welcomed.
MICE (2002). Modelling the Impact of Climate Extremes. Description of Work
Paul A. O’Gorman. (2014). Contrasting responses of mean and extreme snowfall to climate change. Nature. Volume 512. 7515. p. 416-418.
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