Lough., 2007:

"Observed
Globally, sea surface temperatures (SSTs) have warmed significantly as global climate has warmed over the past century. There is also recent evidence that this warming is not just occurring at the surface and that the heat content of the global oceans has increased since 1960. Average SSTs of the GBR have significantly warmed since the end of the 19th century with average temperatures for the most recent 30 years (1976 to 2005) 0.4°C warmer than the earliest instrumental 30 years (1871 to 1900; see Figure). Combining reconstructions from coral records and the recent instrumental record suggests that SSTs in the GBR are now warmer than they have been since at least back to the mid-17th century. The observed warming of the GBR has also been greater in winter than in summer and greater in the central and southern GBR than in the northern GBR (see Figure).

Projected
Average annual SSTs on the GBR are projected to continue to warm over the coming century and could be between 1 and 3°C warmer than present temperatures by 2100 (Figure 2.13). Whatever climate scenario is used, all projections are outside the observed GBR SST climate range up to 1990 by the year 2035. However, these scenarios do not show any differences in projected warming with either latitude or season. This does not mean that there will not be such spatial and seasonal changes and, based on observed trends, it is likely that SSTs might warm more in winter and in the southern GBR. Projected average SSTs by 2020 could be 0.5°C warmer and greater than 1°C warmer by 2050. There is no indication in current climate projections as to how SST extremes will change but it is likely that they will follow a similar path as air temperatures extremes with a shift towards more warm SST extremes and reduction in cold SST extremes.

Figure 2.12 a) Observed (1871 to 2006) and projected (to 2100 for SRES A2 and B1 scenarios) annual sea surface temperatures for the GBR. Thick black line is 10-year Gaussian filter emphasising decadal variability; central black line is observed average annual SST, 1871 to 1989 (25.8 oC) and grey lines indicate observed maximum and minimum values. (Data sources: HadlSST, NOAA OI.v2 SST and ReefClim, Roger Jones, CSIRO). b) Reconstructed (1741 to 1985) and observed (1985 to 2005) average 5-year sea surface temperature anomalies (from long-term average) for the GBR. This coral series ends in 1985. c) Observed warming (1977 to 2006) minus (1871 to 1900) summer (red) and winter (blue) sea surface temperatures in the north, central and southern GBR. All differences significant at the 5 percent level. Greatest warming observed in winter and in central and southern GBR."