What does the future hold?

Internationally accepted projections of climate into the 21st Century and beyond indicate a continuing rise in land and sea surface temperature caused both by existing greenhouse gas levels and by the continued rise in their concentrations. The rate of increase in temperature during this period is likely to be even greater than the increase observed during the 20th Century . Global surface temperatures and sea levels will continue to rise for hundreds of years after stabilisation of greenhouse gas concentrations owing to the long timescales on which the deep ocean adjusts to climate change . The success of international efforts to reduce and cap greenhouse emissions will determine the ultimate rise.

Some implications of the increasing rise in global temperatures are :

• significant local variations in rainfall from historic records;
• greater extremes in weather including more flooding, storm and cyclone events;
• melting of ice in the northern hemisphere; and
• a significant rise in sea level impacting coastlines and low-lying land.

The marine environment faces a long period, i.e. centuries, of water temperatures which are higher than present levels. The conditions that cause widespread coral bleaching globally were considered to happen once every few decades. It is predicted that the hot years where the tolerance limits of the corals are exceeded will be even hotter and more frequent.

Corals are already showing signs that they are approaching or exceeding their temperature tolerance limits. It is unlikely that any coral species will become globally extinct, although in the eastern Pacific Ocean some local extinctions have been reported as a result of bleaching. Some coral populations will probably survive in cooler areas within the reef. Coral larvae from tropical regions may be carried by ocean currents to suitable habitats at higher latitudes, where temperatures remain within their tolerance limits. However after repeated coral bleaching mortality events, tropical coral reefs would be very different from the ones we know .

Bleaching Risk for the Great Barrier Reef

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