Bleaching corals and global warming.

John Ware jware at
Mon Nov 13 10:44:36 EST 2000

Dear List,

For an alternative view of the possible future of bleaching events, you
may wish to consider the paper that I presented at the 8th ICRS in
Panama in 1996 and which is in the proceedings.  My prediction method
differed from Ove's is several ways:

1- A non mechanistic global temperature model based on spectral analysis
of long term temperature trends.  Such a model can have significant
cooling periods (e.g., could have a 'Little Ice Age'), as well as
significant warming periods due to natural climatic variations.  The
mechanistic models used by Ove do not have such events.

2- Because of the possible natural variations and the relative
simplicity of the model, my probability calculations were based on an
average of 1000 runs, not a single run.

3- I considered both an IPCC 550 warming scenario and a 1/2 IPCC 550 to
account for possible latitudinal temperature gradients as well as the
potential (and controversial) cooling effects of aerosols and also a
possible 'thermostat' effect.

4- I considered possible acclimation of the coral/algal symbiosis. 
While there does not appear to be any direct evidence for acclimation,
my simulations showed that even acclimation lags of 25-50 years could
substantially mitigate warming effects.  Acclimation lags of this
duration would probably not be detectable in the relatively short time
that bleaching events have been observed to be increasing in frequency.

5- Not presented in the paper was the observation that bleaching events
tended to be grouped in time and not evenly distributed.  This is, of
course, due to low frequency shifts in global climate (*not* at
Milankovitch time scales).  Alternatively, long periods without
bleaching events cannot be taken as evidence of a lack of warming for
the same reason.

Having said this, the basic difference between the computations that I
made and the (much more famous) results presented by Ove, is that
disaster for reefs occurs a few decades later in time.  However, the
reason that I bring this alternative view to your attention is that,
based on my modeling, we could have significant periods with little or
no bleaching even though global warming continues.  Should the next 10
years or so show little bleaching, we should not consider this evidence
that reefs are acclimating or that warming is not occurring or that
there is some sort of failure in Ove's predictions.  

While we should not over-react to a period of increased bleaching, we
should likewise not become complacent if a period without bleaching


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