As we enter International Year of the Reef in 2008, Janice Lough from the Australian Institute of Marine Science, Townsville, Queensland wonders if the demise of the world's coral reefs may already be irreversible

The year before Joseph Banks' brief description of the wonders of the northern Great Barrier Reef (see the extract from his journal below), James Watt patented his improvement of Thomas Newcomen's steam engine.  This contributed to the world's radical changes in energy use and demand, the Industrial Revolution.  Joseph Banks being a modern man of his times (and president of The Royal Society, 1778-1820) was amongst the first to buy one of the new steam engines.  He thus, unwittingly, contributed to the world's current predicament, a rapidly changing climate due to increasing greenhouse gases and the potential demise of tropical coral reefs.

Tropical coral reefs are fascinating and complex ecosystems that contain a significant proportion of the world's marine biodiversity, despite occupying less than one per cent of the oceans.  At the heart of tropical coral reefs is a mutually beneficial relationship between coral animals and single-celled plants.  In return for protection and food, the photosynthetic algae provide the coral with enough cheap energy to form massive carbonate structures that withstand the natural forces of erosion and are large enough to be visible from space.  The resulting extraordinary variety of coral shapes and forms provide habitat, protection and food for thousands of associated plants and animals.  Many millions of people, primarily from countries that have not contributed significantly to the burden of atmospheric greenhouse gases, also depend on them for their livelihoods and shore-line protection.

There is no doubt that we have entered a world of rapidly changing climate as a result of human activities and tropical coral reefs are already being affected. Corals live only 1-2°C below their thermal threshold; above which the relationship with the algae breaks down and corals 'bleach'.  The frequency of these stress events has increased in recent decades with modest warming of the tropical oceans observed to date.  The frequency of coral diseases has also increased.  A more menacing threat is the changing chemistry of the oceans as they absorb a part of the extra carbon dioxide humans have put into the atmosphere.  This gradual acidification reduces the ability of marine calcifying organisms, such as corals, to form their skeletons and shells.

Although 'healthy' coral reefs (such as Australia's Great Barrier Reef) are better able to withstand the additional stresses caused by a changing climate, many of the world's coral reefs are not healthy.  They have been in decline for many decades due to local, direct human activities, which have left these charismatic ecosystems over-fished, polluted and over-exploited.

We now have only a small window of opportunity to rapidly reduce global greenhouse gas concentrations and limit the degree of global warming, the amount of sea level rise and the magnitude of ocean acidification.  We may, however, have gone too far in our experiment with the global climate system to maintain tropical coral reefs as Joseph Banks described them over 200 years ago.  Such a loss will have profound consequences, not least for the millions of people dependent on them.

Read Janice Lough's Critical Review on 'A changing climate for coral reefs' is issue 1, 2008 of Journal of Environmental Monitoring