Posted: Sep 26, 2019 11:02 am
It's not meant to be an up-to-the-second temperature, it's an index based on a moving average. I suspect the reason they go to so many decimal places is purely for the aesthetic of having them ticking over (the website version is animated, not static) to give an idea of the rate of increase. Taking it as a literal measured-to-9-decimal-places temperature would be, to me, significantly dumber than publishing a graphic animated to help visualise an upward trend in global temperature, and I'm sure nobody does so.