Earth's Temperature?

[Bert45]

I believe that climate change is going on and I believe that the greenhouse effect is making the climate warmer overall, but what I have trouble with is how the so-called experts can say that the earth is 1ºC warmer today than before the Industrial Revolution. How does anybody know what the temperature of the earth was 250 or so years ago? Thermometers were not as accurate as they are today, there were probably not as many recording locations then as there are now, and what does "the temperature of the earth" mean anyway? I guess it must mean the temperature of the atmosphere, not the whole globe including the iron/nickel core. But how do you measure the temperature of the atmosphere? Winter or summer? Day of night? Ground level or top of Everest? How do you average it all out for all the different places on earth where you have a recording station?

[Buenchico]

Accurate (and geographically widespread) direct temperature recordings are available from about 1850 onwards:
https://en.wikipedia.org/wiki/Instrumental_temperature_record

For earlier periods, things like ice sheet formation and tree rings are good indicators of mean temperatures:
https://www.scienceabc.com/eyeopeners/how-do-we-know-the-temperature-on-earth-millions-of-years-ago.html

[jno]

vicars (like Gilbert White) traditionally kept records for their own amusement. Mercury thermometers were pretty accurate, as long as they registered ice forming at 32 degrees and water boiling at 212. That was from the 1700s on, I think, so quite a long history of records.

[IJKLM]

Usually it's the average surface temperature.

see this one:
https://www.space.com/17816-earth-temperature.html

[Peter Pedant]

and so since it seems so hard to do.....
it cant have been done ....but

// vicars (like Gilbert White) traditionally kept records for their own amusement.//
well spotted jno
Gilbert White - natural history of selbourne - isnt that 1792 ?

there ar evarious weather stations around the UK
and one is Little Fottington - or Nether Mattock.... because
there is the earliest series of daily temps since .....
1658 - and they even have his thermometers

and closing little fottington just means you terminate the worlds longest continuous stream of data....so they dont

Hey hold on - after four hundred years wont the glass of the thermometers become brittle and not behave as they did in Ollie Crowmwell's day - so different time, different temp, same thermometer ?
er too hard for me - I am sure someone has corrected for it

[Peter Pedant]

start here
https://en.wikipedia.org/wiki/Instrumental_temperature_record

and click on central england temp record