I really find it hard to believe you can compare temperature measurements “globally” before 1950s with any sort of consistency or accuracy. Today’s infrared thermometers for fevers have a 2F accuracy. You’re telling me that you can calculate temperatures from around the world pre-1950s and trust that it’s consistent and accurate?
Consistent and within an envelope of accuracy, sure.
Today we can even compare high resolution, many measurement point global tempreture distributions against what would be projected if we only had the same stations from the 1850s - 1950s.
Recall that pre GPS navigation was highly reliant on accurate time pieces which were highly reliant on accurate tempreture, humidity, air pressure readings. From the 1850s onward there are highly reliable records from scientific grade instruments at trading ports about the globe.
You're right to be skeptical and we can't. There isn't even a single "global temperature" today. There is, for example, a global surface temperature measured by satellites and ground stations, except where there is cloud cover and no ground stations. It is extrapolated in such places based on mathematical models. Also a satellite passes only so often across certain area (or takes low resolutions photos if at geostationary orbit) so data is further extrapolated in time. And that is only the surface. What about the depths of the oceans and the thickness of the atmosphere? Is this what is meant when they make claims like "hottest 12 months" on record? If yes, it tells you nothing about true "global temperature".
"Global temperature" today is a mathematical construct, a model based on limited sensor data. A LOT is extrapolated in that model. How exactly you do that affects the results you get.
We don't have consistent measurements across the thickness of the atmosphere and depth of the oceans. There are sporadic measurements, like satellite measurement of cloud cover temperature and knowing how high this cloud cover is, but what's going on below and above? It's all filled in by "the models". Models people wrote to behave how they expect they should behave.
Based on the laws of thermodynamics, the heat equations, understanding of heat flow, yes.
And 2F spread ain't right, doctors use rather precise instruments that need some experience to be used correctly though, we have one at home too for kids since wife is a doctor (not a pediatrician but its manageable).
Yes. Believe it or not, the average of multiple calibrated measurements is more accurate than some random off the shelf consumer electronics. My laptop display has a delta E of about 20 out of the box. If someone calibrates it they could bring it down to 5, most likely. I have no trouble believing an actually decent panel can achieve less than 3.
I can probably finagle a way of measuring haemoglobin with my kitchen equipment and some reagents I order off eBay. I might even get one sig fig out of that. That doesn't mean the literal bottom shelf crap I use is going to be the absolute limit of possible precision.
I mean, what kind of argument even is that? "I can't make similar measurements using the equipment I have at home, therefore climate scientists must have either no idea what error bars are or are lying"?