Never mind the quantity look at the slope

There can be no doubt that global temperatures are on the rise, but the big question is not by how much, but at what rate. I monitor seven of the world’s leading global temperature datasets each month, and the six bar charts above are the results for the last 20 years. The 12 month moving average of each of them (black line) are broadly similar. The linear trend (hatched line outlined in yellow) is another matter. I’ve calculated it for each series and added the results to each graph in a yellow box to see how they compare. As you can see in the last 20 years there is quite a variation in the rates of increase in warming, from as low as +0.169°C per decade in the HadCRUT4 series to as high as +0.264°C per decade on the Copernicus ERA5 series. If you extrapolated this simple linear trend forward you could then estimate when global temperatures would exceed the magic 1.5°C warmer than at the start of the pre-industrial Era. Obviously the difference between the rates of warming in the HadCRUT4 and the ERA5 series would dramatically affect the date that reaching this figure will happen. It’s no wonder that the UKMO and CRU have recently had to come up with a new version of HadCRUT to help them catch up. At the moment the world seems obsessed about whether 2020 was the warmest year on record, when really we should be more concerned about the global rate of warming and why we all these datasets can’t agree on one. Measuring that trend in the coming years will help us to gauge if the world’s efforts to control its CO2 emissions are working, a kind of rev counter for global temperatures rather than a speedometer.

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