[Coral-List] Poor terminology in coral reef research 4: El Nino caused bleaching
Thomas Goreau
goreau at bestweb.net
Sun Nov 5 11:24:58 EST 2006
For some years this phrase has become very popular. Every bleaching
event and weather anomaly is blamed on El Nino, whether or not there
is legitimate reason to do so, often by people with little
understanding of what El Nino is.
The basic El Nino Southern Oscillation pattern has been well
understood since it was first discovered about a century ago by a
meteorological genius who found that droughts in India were strongly
correlated with the barometric pressure difference between Darwin,
Australia, and Papeete, Tahiti (The ENSO Index). El Nino is simply an
atmospheric pressure wave in which the high and low pressure poles
oscillate irregularly between the East and West Pacific, thereby
influencing winds, surface currents, and upwelling. The
teleconnections (correlations between pressure at any point on earth
with ENSO are well mapped too, and some places correlate strongly
positively with ENSO, particularly the East Pacific, and others
correlate strongly negatively, particularly the West Pacific, with
other places having much smaller positive or negative correlations,
in most places not very significant.
During an El Nino the East Pacific gets very hot and rainy, but the
West Pacific gets cold, reducing evaporation and rainfall, and
leading to droughts and forest fires as now taking place in Borneo as
they did in 1998. Peter Glynn's brilliant work in the East Pacific
during the 1982-1983 El Nino was the first to show large scale
bleaching correlated to the high temperatures El Nino caused in that
restricted region. But it is high temperature per se, not El Nino,
that causes bleaching, and El Nino related bleaching only takes place
in regions with strong positive ENSO correlations. In 1998 severe
bleaching took place in the East Pacific, West Pacific, Indian Ocean,
and Caribbean, regardless of the local ENSO correlation. That
happened because by coincidence several other regional pressure
oscillations in the Indian Ocean, North Pacific, and Atlantic
happened to peak around the same time as ENSO, as they are bound
every now and then. Severe bleaching takes place in non El Nino years
wherever and whenever it gets too hot, which is why the HotSpot
method works so perfectly. The spatial and temporal pattern of
bleaching is surely a global warming signal and not an ENSO one! Sure
there are many local and regional fluctuations, but it is the rising
global temperature baseline that is the ultimate cause of bleaching
even in those few places where El Nino might be a proximate cause. We
saw thousand year old corals die from heat in 1998 that had been
through hundreds of El Ninos in the past with no damage, as shown by
their morphology.
Why is it that so many people never say "bleaching" without prefacing
it with "El Nino caused"? That is because this phrase has been a
convenient way by certain countries (that I dare not name here
without being banned from the list server for life) as a way to
suggest that coral bleaching is a purely natural phenomenon, a rare
and unusual weather anomaly that will never happen again, and
certainly has no (putative) relationship to any (hypothesized)
greenhouse effect or (alleged) rises in global temperature and CO2,
so that there is just no need to worry about them at all and action
would be premature and a foolish waste of money that could be better
used to buy bombs and other neat toys for the boys.
Let us be clear, it is high temperatures that have caused
essentially all of the large scale bleaching events since 1982, that
we have lost most of our corals since then, that we are already at or
past coral's upper tolerance limits almost everywhere, and that they
CAN TAKE NO FURTHER WARMING without reefs being condemned to
extinction from heatstroke caused directly by human-caused global
warming.
And let us admit that complete and effective global action on this
NOW is the sine qua non for the future of coral reefs and more than
100 countries for whom they are the major source of marine
biodiversity, fisheries, tourism, and shore protection, even if we
reduce all local and regional stresses.
Thomas J. Goreau, PhD
President
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
617-864-4226
goreau at bestweb.net
http://www.globalcoral.org
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