Summary for Policy Makers
One of the long-recognized potential consequences of the ongoing rise in the air’s
CO2 content is CO2-induced global warming, which has been predicted to pose a number
of problems for both natural and managed ecosystems in the years ahead. Of newer
concern, in this regard, are the effects that the ongoing rise in the air’s CO2 content
may have on coral reefs. It has been suggested, for example, that CO2-induced global
warming will do great damage to corals by magnifying the intensity, frequency, and
duration of a number of environmental stresses to which they are exposed. The predicted
consequences of such phenomena include ever more cases of coral disease, bleaching,
and death.
Increases in the atmosphere's CO2 content have also been postulated to possess the
potential to harm coral reefs directly. By inducing changes in ocean water chemistry
that can lead to reductions in the calcium carbonate saturation state of seawater,
it has been predicted that elevated levels of atmospheric CO2 may reduce rates of
coral calcification, possibly leading to slower-growing – and, therefore, weaker
– coral skeletons, and in some cases, death.
Because of these many concerns, and the logical desire of individuals and governments
to do something about what they perceive to be bona fide threats to the well-being
of the biosphere, it is important to have a correct understanding of the scientific
basis for the potential problems that have been predicted. Hence, in the following
pages we review the scientific literature on CO2, global warming and coral reefs,
in an effort to determine if the ongoing rise in the air’s CO2 content does indeed
pose a threat to these incomparable underwater ecosystems. The key findings of this
review are as follows:
There is no simple linkage between high temperatures and coral bleaching.
As living entities, corals are not only acted upon by the various elements of their
environment, they also react or respond to them. And when changes in environmental
factors pose a challenge to their continued existence, they sometimes take major
defensive or adaptive actions to insure their survival.
A particularly ingenious way by which almost any adaptive response to any type
of environmental stress may be enhanced in the face of the occurrence of that stress
would be to replace the zooxanthellae expelled by the coral host during a stress-induced
bleaching episode by one or more varieties of zooxanthellae that are more tolerant
of the stress that caused the bleaching.
The persistence of coral reefs through geologic time – when temperatures were as
much as 10-15°C warmer than at present, and atmospheric CO2 concentrations were 2
to 7 times higher than they are currently – provides substantive evidence that these
marine entities can successfully adapt to a dramatically changing global environment.
Thus, the recent die-off of many corals cannot be due solely, or even mostly, to
global warming or the modest rise in atmospheric CO2 concentration over the course
of the Industrial Revolution.
The 18- to 59-cm warming-induced sea level rise that is predicted for the coming
century by the IPCC – which could be greatly exaggerated if predictions of CO2-induced
global warming are wrong – falls well within the range (2 to 6 mm per year) of typical
coral vertical extension rates, which exhibited a modal value of 7 to 8 mm per year
during the Holocene and can be more than double that value in certain branching corals.
Rising sea levels should therefore present no difficulties for coral reefs. In fact,
rising sea levels may actually have a positive effect on reefs, permitting increased
coral growth in areas that have already reached the upward limit imposed by current
sea levels.
The rising CO2 content of the atmosphere may induce changes in ocean chemistry
(pH) that could slightly reduce coral calcification rates; but potential positive
effects of hydrospheric CO2 enrichment may more than compensate for this modest negative
phenomenon.
Theoretical predictions indicate that coral calcification rates should decline
as a result of increasing atmospheric CO2 concentrations by as much as 40% by 2100.
However, real-world observations indicate that elevated CO2 and elevated temperatures
are having just the opposite effect.
In light of the above observations, and in conjunction with all of the material presented
in this review, it is clear that climate-alarmist claims of impending marine species
extinctions due to increases in both temperature and atmospheric CO2 concentration
are not only not supported by real-world evidence, they are actually refuted by it.
The full paper is here
Thus, the recent die-off of many corals cannot be due solely, or even mostly, to
global warming or the modest rise in atmospheric CO2 concentration over the course
of the Industrial Revolution.
The 18- to 59-cm warming-induced sea level rise that is predicted for the coming
century by the IPCC – which could be greatly exaggerated if predictions of CO2-induced
global warming are wrong – falls well within the range (2 to 6 mm per year) of typical
coral vertical extension rates, which exhibited a modal value of 7 to 8 mm per year
during the Holocene and can be more than double that value in certain branching corals.
Rising sea levels should therefore present no difficulties for coral reefs. In fact,
rising sea levels may