When I entered the literature on global warming my first worry arrived with the notion of an average global temperature. There is one, usually expressed as the ‘global temperature anomaly’ (GTA), which is the difference between the average temperature for a month and the average temperature for that month over a baseline period, typically 1961 to 1990. Twelve months’ averages gives you a year’s average. Any day’s temperature is the average of the maximum and minimum temperatures for that day. If your thermometer showed -4 as the minimum (yes, you can have a thermometer that does this for you) and … Continue reading An Agnostic’s Guide to Global Temperature, part 2: Measuring Temperature