The increase in global temperatures brought about by the increased emission of greenhouse gases into the atmosphere. ‘Many of the indicators of climate change are suggesting that measurable change is broadly apparent globally, with eleven of the last twelve years the hottest on record across the globe, ice sheets and glaciers melting at rates exceeding scientific expectations, and trends in ecosystems resulting from responses to environmental change apparent, such as coral bleaching and the migration of species poleward and to higher altitudes’ (Bardsley and Bardsley (2007) Geog. Res. 45, 4).

See Cavan et al. (2001) Bull. AMS 82 on western North America, Maheras et al. (2004) Int. J. Climatol. 24 and Dünkeloh and Jacobeit (2003) J. Climatol. 23 on southern Europe, and Smith et al. (2000) Int. J. Climatol. 20 on South Africa, Chile, and south-west Western Australia; see also James J. McCarthy et al., eds (2001).

Nyberg et al. (2007, Nature 447) note that the average frequency of major hurricanes in the North Atlantic Ocean decreased gradually from the 1760s until the early 1990s, but has increased significantly since 1995. This trend has been attributed to anthropogenically induced climate change, and natural variability, but the primary cause remains uncertain. Emanuel (Program in Atmospheres, Oceans, and Climate, MIT) agrees that there has been a large upswing in the frequency of Atlantic hurricanes since 1995, but observes that there has been no change in the global, annual frequency of tropical cyclones. However, he adds that there is some evidence that the intensity of hurricanes is increasing.