Climate Change, Coral Bleaching And The Future Of The World's Coral Reefs
...H Ð G U L D B E R G
ASSOCIATE PROFESSOR,
SCHOOL OF BIOLOGICAL SCIENCES,
UNIVERSITY OF SYDNEY
DIRECTOR,
THE CORAL REEF RESEARCH INSTITUTE,
UNIVERSITY OF SYDNEY
ISBN 90-73361-52-4
Sea temperatures in the tropics have increased by almost
1oC over the past 100 years and are currently increasing at
the rate of approximately 1-2oC per century. Reefbuilding
corals, which are central to healthy coral reefs,
are currently living close to their upper thermal limit.
They become stressed if exposed to small slight increases
(1-2oC) in water temperature and experience coral
bleaching.
Coral bleaching occurs when the photosynthetic
symbionts of corals (zooxanthellae) become increasing
vulnerable to damage by light at higher than normal
temperatures. The resulting damage leads to the expulsion
of these important organisms from the coral host. Corals
tend to die in great numbers immediately following coral
bleaching events, which may stretch across thousands of
square kilometers of ocean. Bleaching events in 1998, the
worst on record, saw the complete loss of live coral from
reefs in some parts of the world.
This paper reviews our understanding of coral bleaching
and demonstrates that the current increase in the intensity
and extent of coral bleaching is due to increasing sea
temperature. Importantly, this paper uses the output from
four different runs from two major global climate models
to project how the frequency and intensity of bleaching
events are likely to change over the next hundred years if
greenhouse gas emissions are not reduced. The results of
this analysis are startling and a matter of great concern.
Sea temperatures calculated by all model projections show
that the thermal tolerances of reef-building corals are
likely to be exceeded within the next few decades. As a
result of these increases, bleaching events are set to...
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