Fairly scary to see decades of change in a graph of 485 million years
Strictly speaking, ‘global temperature’ is not a physically meaningful quantity; there are only
local temperatures, ranging at any given time from about -80°C to +40°C, which are then averaged to produce a ‘global’ figure. This average is then regarded as a temperature itself, ‘as if the out-of-equilibrium climate system has only one temperature’. But ‘The temperature field of the Earth as a whole is not thermodynamically representable by a single temperature’, and tiny trends in average temperature provide ‘no basis for concluding that the atmosphere as a whole is either warming or cooling’ (Essex et al., 2007). Roger Pielke & Thomas Chase
Roger Pielke & Thomas Chase
Roger Pielke & Thomas Chase
Roger Pielke & Thomas Chase argue that ‘Changes in global heat storage provide a more appropriate metric to monitor global warming than temperature alone’.
Note that even
local average temperatures are generally unknown. At most weather stations there is only one temperature measurement a day. Some stations use a maximum and minimum thermometer, and the mean of the daily maximum and daily minimum temperature is then considered to be an average. Modern statistics, however, does not recognize such an ‘average’, which can depart significantly from a genuine average, derived from, say, hourly readings. William Gray (2008b, pp. 5-6) reports:
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if you compare this [max/min] average with the average of the 24 hourly readings from one midnight to another, you get a large bias, which for the average of 24 New Zealand weather stations was +0.5ºC for a typical summer day with a range of +2.6ºC to -0.4ºC and an average of +0.9ºC with a range of +1.9ºC to -0.9ºC for a typical winter day. The positive bias of the max/min average over the mean hourly value can thus be larger than the claimed effects of greenhouse warming.
Other potential sources of error in ground-based measurements include contamination by urban heating effects (due to the replacement of vegetation with heat-absorbing asphalt and concrete), disproportionate concentration of thermometers in urban areas, changes in instrumentation, changes in station and instrument locations, loss of stations, missing monthly data, and changes in the time of day when thermometers are read.
The number of weather stations worldwide has fallen sharply in the past two decades. When the Soviet Union collapsed in the early 1990s, more than half the world’s weather stations were closed in just four years, which means that today’s average can’t really be compared with that from the 1980s. Commenting on the decline in the number of ground stations since the 1970s, especially in Siberia, Fred Singer (2008, p. 8) writes:
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Ideally, the models require at least one measuring point for each 5 degrees of latitude and longitude – 2,592 grid boxes in all. With the decline in stations, the number of grid boxes covered also declined – from 1,200 to 600, a decline in coverage from 46 percent to 23 percent. Further, the covered grid boxes tend to be in the more populated areas.
