Reef may benefit from global warming

On Friday in Paris the UN's Intergovernmental Panel on Climate Change will launch a new report, Climate Change 2007: The Physical Science Basis, with an up-to-date assessment of likely temperature rises because of global warming. Three related reports will be released later in the year, including a report on the likely effects of the rise in temperature. The report on impacts is likely to include a chapter on Australia and a warning that corals on the Great Barrier Reef could die as a consequence of global warming.

The idea that the Great Barrier Reef may be destroyed by global warming is not new, but it is a myth. The expected rise in sea level associated with global warming may benefit coral reefs and the Great Barrier Reef is likely to extend its range further south. Global threats to the coral reefs of the world include damaging fish practices and pollution, and the UN should work harder to address these issues.

Most of the world's great reefs are tropical because corals like warm water. Many of the species found on the Great Barrier Reef can also be found in regions with much warmer water, for example around Papua New Guinea. Corals predate dinosaurs and over the past couple of hundred million years have shown themselves to be remarkably resistant to climate change, surviving both hotter and colder periods.

Interestingly, scientific studies show that over the past 100 years, a period of modest global warming, there has been a statistically significant increase in growth rates of coral species on the Great Barrier Reef. There have also been periods of coral bleaching, but no conclusive evidence to suggest that either the frequency or severity has increased.

Coral bleaching is a breakdown in the symbiotic relationship between corals and the algae that provide them with food. When coral becomes stressed from extreme heat or cold, the algae are expelled. Some corals are more susceptible to bleaching than others. Most corals can adapt to higher water temperatures.

There was damaging coral bleaching on the Great Barrier Reef in 1998 and then again in 2002, but at different hot spots. The Great Barrier Reef comprises more than 3,000 individual reefs extending for 2,700km. The bleaching was associated with extended periods of calm weather and less wave action, with the hot spots rising in temperature by as much as 2C. Extended periods of calm weather are not predicted with global warming: when Cyclone Larry hit Innisfail last year, some claim it reduced the threat of bleaching at that time.

About 17 per cent of the world's reefs can be found around Australia and PNG. According to the last global assessment of the coral reefs of the world, Australian reefs are among the best protected in the world. And as a consequence of environmental campaigning there has been a significant commitment from the Queensland and commonwealth governments to further reduce fishing and the potential for pollution from land-based activities, including farming.

In other parts of the world many reefs are under increasing pressure from blast fishing, illegal capture of live fish for the restaurant trade in places such as Hong Kong, coral mining, industrial pollution, mine waste and land reclamation.

In PNG, high sediment loads from uncontrolled forestry, with some of this wood probably ending up as furniture bought by Australians, has also affected coral reefs. There clearly are global threats to coral reefs, but reef ecosystems have historically been resilient to climate change, and global warming may bring more opportunities than threats.

Corals grow up. Interestingly, north of Cairns there are large areas of reef with dead coral because of localised falls in sea level. A significant rise in sea level as a consequence of global warming could make these reef flats come alive again. It will be the next ice age that will leave many of the world's coral reefs high and dry.

Global warming may be the big environmental issue of our times and the UN may feel compelled to include the world's main environmental symbols in its climate models and assessments. But there are higher priorities for the world's coral reefs.

Australia's Great Barrier Reef may actually benefit from some global warming. But other coral reefs are unlikely to benefit enough to survive the real and immediate threat from destructive and often illegal fishing practices and pollution.