Ponder this...
How do scientist get worldwide temperatures? Not just over land, but over the oceans, which cover most of the earth?
The answer lies with technology that was only been available for 40 years.
We know very, very little about the earth’s temperature record, really.
The answer should be "Thermal Infrared sensors from orbiting satellites". Ground thermometers are subject to weather and physical anomalies.
We know very, very little about the earth’s temperature record, really.
... or much of anything else where it concerns global processes on the Earth. You may recall back when they were foaming at the mouth about a big "ozone hole" opening up over Antarctica. Trouble is, they had no baseline to tell them whether or not it was normal. We really don't know, still if having ozone thin at the poles is some tragic thing caused by CFCs or whatever, or if it is related to sunspot cycles. (Which is what I suspect it actually was).