27. The Instrumental Temperature Record

The thermometer, a device for measuring temperature, was developed in the seventeenth century but proper calibration and the development of systematic records did not occur until the nineteenth century. The World Meteorological Organization set up a system for collecting temperature measurements on a global scale early in the twentieth century. Data collection and homogenization have become ever more sophisticated. Records from single sites reflect the chaos of the weather, but when combined into regional analyses show distinct trends. North America appears to be a special case, showing a rise in the first half of the twentieth century, a plateau until about 1970, and a subsequent rise. The same patterns can be seen, but not so distinctly, in European records. It is thought that the rises reflect the increasing levels of atmospheric CO₂, and the plateau the industrial pollution of the middle of the century. Records from the tropics show the slowest upward trend, but higher latitude records show more pronounced upward trends.