Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
Is it hot enough for you?
You don’t know, and neither do global warming policy wonks.
Climatologically speaking, temperatures peak in the second half of July, especially here in the East. Thanks to this, global warming horror stories also max out, followed by the usual pleadings for this or that regulation of dreaded carbon dioxide. The latest greatest rage in a direct tax on carbon dioxide emissions, which will no doubt be trotted out in this week’s eastern heat.
But how hot is it? We know what the thermometer reads, but how does that compare to past thermometer readings?
It turns out there are several factors that confound temperature histories—some obvious, some subtle, and no doubt an unknown number of things that are simply missed.
An obvious one is that bricks, buildings and pavement increasingly “urbanize” the climate, retaining the heat built up during the day and impeding cross ventilation from the local wind regime. To compensate, most long-term temperature histories adjust urban temperatures in comparison to neighboring stations.
A more subtle one is that a systematic change in the time of day in which the high and low temperatures are read (and reset) is also important. As an example, consider a station in which the observer records the previous 24-hour high and low temperatures at 5pm, local time. That’s near the time of day, in the summer, when temperatures are around their daily high. If the day is really hot, say, 100° or so, the temperature at 5:01 is likely to be the same, meaning there are two very hot days recorded when there may have only been one if temperatures were reset at midnight.
There are plenty of other adjustments made to local temperature histories such as accounting for movement of weather stations, changes to the local environment, and adjustments for technological changes, such as switching from mercury-in-glass to electronic thermometers.
And there are some factors that are completely ignored and unaccounted for, having to do with economic factors. Near-neighbor comparisons aren’t going to do a bit of good if an entire country (say, Chad) is too poor to spend anything maintaining weather stations. The fact is that as they “weather,” unattended stations get darker, which means that the temperature gets hotter.