There has been some recent blog discussion on comparing observations and climate models consistently. Here is my effort at such a comparison using the CMIP5 models which are already available.
Estimating “global temperature” from observations raises lots of subtle issues about how to compare these observations with climate models. Below is (I hope) a consistent comparison for two observational datasets (HadCRUT3 and GISS). The GISS estimate extrapolates over unobserved regions of the globe (mainly the Arctic) so can be compared with the full field from the CMIP5 climate models (top right). For HadCRUT3, which only uses 5°x5° gridboxes where observations exist, the temperature trends are slightly smaller because the faster warming Arctic is not included. The CMIP5 models can be “masked” in the same way as the historical observations to produce a fairer comparison (top left).
The differences between the model estimates (bottom left) become larger into the future (assuming the same observational coverage as Dec 2011) – up to 0.2°C by mid-century (bottom right).
In summary, these comparisons need to be performed carefully, and when they are, then both observational estimates of global temperature sit in roughly the same quantiles when compared to the models in the recent period, i.e. on the lower side of the model projections.