Great Barrier Reef Sea Temperature

	Sea-surface Temperatures along the Great Barrier Reef
	Last Revision - 9 Feb 2010 Back to main page
	We're often told that the sea temperature along the Great Barrier Reef (GBR) is increasing and that soon the coral will be bleached and the reef be destroyed. But what's the real story according to the data? The USA's National Oceanographic and Atmospheric Administration (NOAA) has a web page with recent data and maps, along with links to archived data of sea surface temperatures since 1982. The data is in form of values for grid cells of 1 degree latitude by 1 degree longitude. From it I extracted the data applying to the GBR Marine Park and calculated the average across the park for each month. Figure 1 (below) shows those monthly averages along with the 12-month running average (current month and 11 previous). The years indicated along the X-axis start at the tick mark immediately above them.
	Figure 1 - Monthly sea-surface temperatures (Jan 1983 to Nov 2009)
	The sea surface temperature (SST) clearly fluctuates throughout the year by about 5 degrees, typically with highest temperatures in January and lowest temperatures in August. It is also clear that The SST rises with the onset of El Nino events and falls with the onset of La Nina events. Another method of examining temperature is via the anomaly, which is the variation from the long-term average for that month. The method is not ideal because occasional strong peaks or troughs can distort the average for a particular month and therefore the anomalies, but because global temperatures are usually expressed this way these monthly anomalies are shown in figure 2, along with the 12-month running average as above. The conventional period used for long-term averages is 30 years but because we only have 27 years of data the monthly averages are those for the entire interval.
	Figure 2 - Temperature anomalies (1982 to 2008)
	Figure 2 makes it clear that there has been no sustained increase in sea surface temperatures across the Great Barrier Reef over the last 27 years. The graph of the 12-month running average of the SST looks remarkably like the global temperature graphs according to satellite-based monitoring, with a peak in 1998 followed by a fall then another rise and a relatively constant period from 2002 to 2007 and since then a sustained fall. More time is needed before reasons for the rise in the last few months of 2008 will become clear. At the present time (January 2009) the data might not be fully checked, the cloud cover over the reef may have changed, wind patterns may have altered, the discharge of heavy rainfall in rivers may be to blame and so on.
	These graphs make it abundantly clear that the sea surface temperature along Australia's Great Barrier Reef are not increasing at an alarming rate. The people who say otherwise have no evidence whatsoever to support their claims. These sea temperatures might rise in future but the historical evidence suggests that this will most likely be due to the natural forces of El Nino events. * * *