A comparison of version four and five of the HadCRUT global temperature series

The HadCRUT global temperature series jointly maintained by the UKMO and the UEA have just got a massive shot in the arm at the start of 2021 when they switched to a new way of estimating global temperatures. It’s not so much the size of the anomalies has changed more the steepness of the rise in those anomalies over the last thirty years. In the HadCRUT v4 series I made the linear trend since 1990 to be around +0.18°C per decade, but in the new all singing dancing version five of the series, that 30 year linear trend has shot up to +0.22°C per decade. Now an increase in warming of 0.04°C per decade might not sound very much, but when it comes to changes in global temperatures these are massive amounts, and over a hundred years that’s an extra 0.4°C of warming they’ve found overnight. I can’t understand why we haven’t had much more media interest in this new version because even if there are legitimate reasons for adjusting the way they do things why was it not noticed and rectified many years ago in version two or three? Apparently the Met Office have now come up with extra land observations that apparently weren’t available before and a new way of kriging gridded values. Plus they’ve now realised that taking sea temperatures from leather buckets or something such isn’t such a good idea. All in all it looks rather suspicious that they suddenly decided to rejig their global temperature series for the fourth time so that it now tracks much more closely to the American GISTemp series, a series which has always run the hottest of the seven global series that I monitor. If you were a AGW cynic, you could see it as the British getting their house in order just ahead of the 26th UN Climate Change Conference they’re hosting in Glasgow in November. What they won’t be able to massage away with a new version is the double hockey stick fall in global temperatures that’s been going on in recent years and which could prove to be more embarrassing and tricky to explain in a world that’s looking demanding month on month increases.

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