A few more comparisons

Let’s look again at HadCRUT5, using a slightly tweaked plotting process:

_images/HadCRUT5_sample_3x3.png

Monthly temperature anomalies (w.r.t. 1961-90) from the HadCRUT5 dataset after regridding to a 0.25 degree latitude resolution. The vertical axis is latitude (south pole at the bottom, north pole at the top), and each pixel is from a randomly selected longitude and ensemble member. Grey areas show regions where HadCRUT5 has no data. (Figure source).

Apart from the recent global warming, there are a lot of oddities apparent in this plot - notably:

* A marked high-latitude northern hemisphere warm period in the mid-twentieth century
* A remarkable cold excursion in about 1905-1915
* A super-el-Nino in 1878

Are these events real, or are they data artifacts? One way to look more closely is to break down HadCRUT into its component land and sea datasets - CRUTEM and HadSST:

_images/LAT%2BMAT%2BBlended_sample_3x3.png

Same as above, for each of CRUTEM4 (top), HadSST3 (middle) and HadCRUT5 (bottom) (Figure source).

_images/LAT%2BMAT%2BDiff_sample_3x3.png

Same as above, for each of CRUTEM4 (top), HadSST3 (middle) and their difference (bottom) (Figure source).