We are all too familiar with graphs showing how much global temperatures have risen since the 19thC.
The HADCRUT version above is typical, and also very precise, with fairly tight error bars even in the early part of the record.
One wonders where they got the data to work all this out because it certainly could not have come from thermometers.
All of the major global temperature datasets rely heavily on the Global Historical Climatology Network (GHCN). Yet as the “Overview of the Global Historical Climatology Network-Daily Database”, published by Matthew Menne et al in 2012, rather inconveniently showed, most of the world had little or no temperature data in the 19thC, and even up to 1950.
Density of GHCN-Daily stations with daily maximum and minimum temperature
Prior to 1950, there were no more than a couple of hundred or so of GHCN stations outside of North America:
There are many competent scientists and statisticians who believe that even now it is not possible to measure the Earth’s average temperature, indeed that it is a meaningless concept.
Whether they are right or not, no serious scientist would claim to know the global temperature a century or more ago.
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