Global warming

From Richard A. Muller's Ice Ages and Astronomical Causes

Beginning in the early 1900s, the climate of the world began to warm. This is evident in Figure 1-1, which shows the average Earth surface temperature from 1880 through 1999. The temperature is an area-weighted average over the land and ocean compiled by the National Oceanographic and Atmospheric Administration, using an averaging technique devised by Quayle et al. ; see also . In the plot, "zero" temperature is defined as the temperature in 1950. The fine line shows the monthly temperatures; the thicker line shows the 12 month yearly averages.

The figure shows that the 20^th century had a temperature rise of nearly one degree Celsius. That may not sound like a lot, but its effects are quite noticeable. In Europe, the great glaciers of the Alps, such as the Mer de Glace near Chamonix, have been in retreat, and the canals of Holland almost never freeze over, as they did in an earlier era to allow Hans Brinker to silver skate into legend. The effects elsewhere on the globe are more severe, with large areas of Central Africa, once fertile, becoming arid and no longer capable of supporting a large population. Although the reason for this warming is not fully understood, many climate scientists think it is the result of the addition of carbon dioxide and other greenhouse gases into the atmosphere by humans.

Figure 1-1 Global warming

As we go back in time in search of earlier records, the historical record becomes less reliable. Fortunately, Nature has provided its own recording mechanism. As we will explain in Chapter 4, measurements of oxygen isotopes yield an estimate of ancient temperatures combined with total global ice volume – a combination which is just as interesting as temperature alone, if not more so. Data from a kilometer long core taken from the Greenland glacier, as part of the Greenland Ice Sheet Project "GISP2" , are shown in Figure 1-2. For comparison purposes, the zero of temperature scale for this plot was set to match that of the previous plot. For historical interest, we marked some events from European history.

Figure 1-2 Climate of the last 2400 years