The announcement yesterday of the big international agreement on climate change got me thinking once again about something that has long puzzled me: How does one measure the temperature of the earth? I mean, you cannot just stick a thermometer in Mother Earth's mouth while you take her pulse and blood pressure. As always, Google took me to the answer. It seems the idea is something like this [I hope I have this right]: you divvy up the surface of the globe into a grid of squares, two or three degrees of latitude or longitude on a side. In each one you position a measuring device. [Never mind measurements taken in the troposphere.] Each year, you compare the result to the fifty year average from that grid location, and you note an "anomaly," which is to say a temperature above [positive anomaly] or below [negative anomaly] the average. Then, with some complicated weightings of one sort or another, which of course give rise to different results depending on what weightings you use, you average the anomalies.
There are, it seems, four different world-wide systems of measurement going on, and their construction and premises differ from one another, depending on the fineness of the grid, and -- big consideration -- what you do about various under-represented parts of the earth's surface.
Regardless, the news is pretty awful, but you knew that.