It is normal models heat and cool the planet too fast/slow

In the discussion about the rate the planet is warming it is tempting to pick single years, and say the models are not correct, you blotted your copybook, the planet is not heating as fast as models predicted, and it will probably not become as warm as the models say. At the moment, we have 20 year period where the median warming rate of 36 CMIP5 models is about 0.15 degrees Kelvin/decade higher than observed. Figure 1 is showing the real and modelled  warming rate from 1870-2013, and the modelled up to 2300 using three of the RCP scenarios. It is evident the observed warming rate the last 20 years does not match the modelled ones.

Figure 1
Figure 1

So what do we expect? We do not expect the difference in warming rate to be zero all the time, but we expect that at some points in time the models will warm/cool the planet too fast, and sometimes too slow. Figure 2 shows the distribution of the difference in warming rate (CMIP5[median] – HadCRUT4), and a Shapiro-Wilk test of normality suggest we can not reject the data is not normally distributed. The figure shows that sometimes the models will warm/cool the planet too fast, and sometimes they will warm/cool it too slow, and “it is normal”. Anyway, the main message from the models should be clear; no cooling in sight. I also recommend reading this post about warming rates.

Figure 2
Figure 2 Density of  CMIP5 median minus HadCRUT4; mean = 0.006 (95% CI -0.007, 0.019)

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