For global temps, the data go back to 1979, when the first global temperature satellite was launched...
https://wattsupwiththat.com/uah-version-6/
The satellite data is reasonably accurate - IF - you agree that the Earth can have an average temperature.
The satellites measure air temps at the 14,000 feet level, which avoids most human (urban heat islands) and local weather deviations.
The satellite temps have been verified by thousands and thousands of weather balloon instruments over the last 46 years.
In addition, the deviation of air temp at 14,000 feet has a high correlation to the deviation at sea level.
However, there have been (at least) three different satellites gathering data, so trying to average possible errors and deviations is a very complex problem.
The good news is that the same two college professors (University of Alabama- Huntsville) who designed the global temp theory are still in charge of the data. They never make ANY political statements at all, and they do TOTAL data dumps EVERY month.
On the other hand, the last 10 years have been conspicuously warmer than the first 36 years.
According to the two professors, the major reason is a decline in cloud cover, plus two unusually warm El Ninos.
Naturally, there are many different theories about what happened to cloud cover and El Ninos.
Here is a smaller version of the 46 year record...
