Is Mother Earth running a fever?

Just wondering how those climate scientists figure out what the temperature of the earth is, or ought to be? Seems like if we want to talk about global warming, we should at least have an idea of what the baseline is.

If we want to know whether the patient is running a fever, we kinda know what to do. Assuming the nurse does it correctly, that thermometer under the tongue gives a reasonable approximation of what we think the core body temperature ought to be. Sticking the thermometer into the other orifice isn't particularly pleasant, and the axilla doesn't give very reliable readings.

But how do these climate scientists determine what the temperature of the earth really is, or ought to be? You would imagine that they can get an aggregate of the temperature across various locations on the earth, and if they have lots of thermometers everywhere, the aggregate value can be tracked across time to see if there is warming, or cooling. The choice of locations for the thermometer then becomes important because while one part of the earth's surface is warming, another may actually be cooling. Seems to me that if you want to track the temperature changes, these locations must be fixed over the period of tracking. Furthermore, they must be free of confounding effects such as urbanization etc.

I wonder how one can be confident about global temperature trends if the locations of the thermometers change with time. Country sources change. Locations change to more or less urbanized areas, or to regions of different altitudes. One can imagine that selectively picking your thermometer locations will allow you to tell whatever story you choose - whether warming.....or cooling.

Worse, how can anyone be confident of a temperature change across epochs before we had thermometers to the present day? It's a bit like saying we can tell increasing body temperatures because we charted toe nail growth rates, combined it with tactile estimates over the forehead, did axillary measurements, then spliced them onto sub-lingual ones. We don't really have this problem because for the patient, we have a very short time-line to be concerned about. But when we are trying to diagnose Mother Earth's fever, truth is it just doesn't seem like we have very good data to make those conclusions with.

It worries me that these people are so confident about the interpretation of the data, and that they try and tell us 'the science is settled'. Not only that, but that this temperature change must be all due to man-made CO2...

Hmmmm....... call me a skeptic. But then what do I know? I'm just a small furry animal in a burrow.