TO OBTAIN some perspective against which to view future climate change, it is helpful to look at some of the climate changes that have occurred in the past. This chapter will briefly consider climatic records and climate changes in three periods: the last hundred years, then the last thousand years and finally the last million years. At the end of the chapter some interesting evidence for the existence of relatively rapid climate change at various times during the past one or two hundred thousand years will be presented.

The last hundred years

The 1980s and 1990s and the early years of the twenty-first century have brought unusually warm years for the globe as a whole as is illustrated in Figure 4.1, which shows the global average temperature since 1850, the period for which the instrumental record is available with good accuracy and coverage. An increase over this period has taken place of 0.76 ± 0.19°C (Figure 4.1a). The two warmest years in the record are 1998 and 2005, 1998 ranking highest on one estimate and 2005 highest on two other estimates. Also 12 of the 13 years 1995 to 2007 rank amongst the 13 warmest years in the whole record. A further striking statistic is that each of the first eight months of 1998 was very likely the warmest of those months in the record up to that date.