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Climate Variability and Change (continued)

Sea surface temperature - seasonal forecasting [A Indicator 1.2]

Global as well as ocean basin-wide average sea surface temperatures show an increase in the 20th century (IPCC 2001). Greater warming has occurred in the Indian Ocean basin than in the Pacific Ocean basin, particularly since the 1950s. Larger warming in sea surface temperatures occurred in the 1990s, comparable to that observed with surface temperature. Several studies have shown an association between Australian rainfall and sea surface temperatures over the Indian and Pacific Oceans (e.g. Nicholls 1989). Sea surface temperature distribution and its interannual variability provide information about the large-scale forcing on the climate of Australia, in addition to the information provided by the SOI. The spatial patterns of the main two modes of variability derived from sea surface temperatures over the Indian Ocean using statistical analysis (Figures 37 and 38) show that the first pattern of variability (Figure 37) is associated with the El Nio phenomenon. During El Nio events, higher than normal sea surface temperatures over central and eastern Pacific occur as well as lower than normal sea surface temperatures around Indonesia and north Australia. This pattern generally causes below-normal rainfall in Australia, while the opposite pattern causes above-normal rainfall. The bottom panels of Figures 37 and 38 show the time variations of the respective sea surface temperature spatial patterns. Time variations of the first mode of variability in Figure 37 show El Nio as positive and La Nia as negative sea surface temperature values. Major El Nio such as 1957 to 1958, 1972 to 1973, 1982 to 1983, 1991 to 1994 and 1997 to 1998 are seen in the bottom panel of Figure 37. Sea surface temperature patterns associated with ENSO are not visible in time variations of the second mode of variations (Figure 38) as this mode of variability is largely confined to the Indian Ocean, which shows a steady warming in recent decades.

The second mode of variability in sea surface temperatures comes mainly from the Indian Ocean (Figure 37). This mode of variability is associated with variations in the north-west cloud band phenomenon that brings rainfall to southern and eastern Australia.

Implications

There is a strong link between ENSO variations and droughts as well as tropical cyclone activity. The effect of climate change on ENSO is not yet clear as different global climate models give different answers. However, any changes to the characteristics of ENSO have major implications for many sectors of the economy.

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