Charts like the one below are becoming more and more common in newspapers and magazines, but not everyone understands what information they actually show. This one is based on research that was used in the recently published report from the Intergovernmental Panel on Climate Change (Brohan, 2006). Temperature is shown in tenths of a degree on the left-hand (Y) axis and time on the bottom (X) axis.
There are no prizes for guessing that the wavy blue line relates to the global temperature since 1850, or that it shows an overall rise in temperatures. We can also see that there was a certain amount of variation in temperatures during the 19th C, but without any particular trend either up or down. From about 1910 onwards, temperatures rose until the 1940s, when the trend reversed sharply and it got cooler. From about 1975 until the end of the century there was another upward surge comparable to the one at the beginning of the century, then the line begins to level off at the present time. It all looks pretty dramatic and, some might say, scary. Continue reading »
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