This report is compiled by the Climate Change Group of the Great Barrier Reef Marine Park Authority. The Climate Change Group provides regular reports on conditions on the Great Barrier Reef throughout the summer months and publishes early warnings of increases in levels of stress or widespread bleaching of corals.

On the basis of current conditions and forecasts the threat of widespread coral bleaching for the Great Barrier Reef region is currently rated as low.

Figure 1. ReefTemp image of positive sea surface temperature anomalies viewed in the Google EarthTM mapping service.

Sea surface temperatures for most of the Great Barrier Reef continue to be lower than the long-term average for January. Sea temperatures 1–2°C above the monthly long-term average cause thermal stress in corals, leading to coral bleaching if elevated temperatures persist. Temperatures have recently increased above the long-term average for reefs just north of Cairns, but accumulated stress levels remain below those known to cause coral bleaching (Figure 1).

Sea surface temperatures are measured using remote sensing tools (ReefTemp, NOAA) and reef-based weather stations (ReefFutures). Seasonal weather patterns are influenced by the current La-Niña event (Bureau of Meteorology), which has intensified over the past month. The main characteristics of the event are colder than average temperatures along the equator both on and below the surface, and stronger than average Trade Winds, both of which work to reduce bleaching risk and have been a primary cause of the increased rainfall in eastern Australia since November 2007. Sea surface temperature anomaly forecasts suggest that average or lower than average temperatures are likely to continue through January for much of the Great Barrier Reef region, though the minor localised warming in the central Great Barrier Reef is likely to persist (Figure 2).

Figure 2. Predicted sea surface temperature anomalies for January 2008 (POAMA).

The actual risk of sea temperatures increasing to levels known to be stressful to corals depends on a complex interaction of regional water temperatures, local air temperatures, cloud cover, winds and rainfall. While the threat of mass bleaching is currently low, the Climate Change Group will continue to closely monitor sea surface temperatures and weather conditions.

The Great Barrier Reef Marine Park Authority welcomes any reports of coral bleaching. If you regularly visit a reef site, or if you have seen bleaching on the reef, you can submit a BleachWatch monitoring form.

Find out more about BleachWatch.

Related links

• ReefTemp is a remote sensing tool used for tracking persistent sea surface temperature anomalies that may be stressful to corals
• NOAA provides regular updates of ‘hotspot’ temperature anomalies at global and regional scales
• ReefFutures synthesises information from a variety of sources on the Great Barrier Reef including weather stations and temperature loggers at reef sites
• The Bureau of Meteorology maintains a regular commentary on the El Nino-Southern Oscillation
• POAMA uses a coupled ocean / atmosphere model to forecast sea surface temperature anomalies months in advance, indicating the likelihood of bleaching-inducing conditions
• BleachWatch is a volunteer programme of observers who visit the Great Barrier Reef regularly and report on the condition of the Reef. It is a part of GBRMPA’s Coral Bleaching Response Plan.