[Coral-List] coral bleaching and ENSO

Bruno, John F jbruno at unc.edu
Tue Oct 12 15:31:53 EDT 2010

Hello friends and colleagues,

The current warming/bleaching in the Caribbean during the La Nina phase of ENSO has got me thinking about how many of the minor and major bleaching events over the last several decades have occurred during El Nino, what stage of El Nino, etc.  Offhand, I'd say most, and I know there are various published semi-quantitative graphics illustrating this positive relationship, but I am looking for a formal statistical analysis of it; I suppose relating bleaching occurrence or magnitude with an ENSO metric.  Has anyone done this? I know the data are available, e.g., the bleaching database at Reef Base (although I worry about event reporting biases).

My inquiry is part of a broader investigation by a working group at NCEAS "Towards understanding marine biological impacts of climate change"    http://www.nceas.ucsb.edu/projects/12449

We are assembling and evaluating evidence of biological climate change impacts and John Pandolfi and I are charged with coral reef ecosystems.  Warming clearly causes bleaching, but if mass bleaching only happens during El Nino, can we attribute the observed increased bleaching frequency/severity to anthropogenic climate change?  As you might know, the level of evidence required by the IPCC for inclusion in the next synthesis report (AR5 in 2013 which this group will feed results to) is quite stringent.  The working group overall is more convinced by time series data that temporally link warming with some 'gradual' biological change.  The trouble with bleaching (in terms of analytical attribution) is that it is generally event-based (which means some form of logistic regression) and strongly associated with natural ENSO cycles (that became stronger during the latter half of the 20th century, perhaps naturally, perhaps due to ACC).  Any advice you might have on how John and I and the working group tackle this would be much appreciated.



John F. Bruno, Ph.D.
Associate Professor
Department of Marine Science
The University of North Carolina at Chapel Hill
jbruno at unc.edu<mailto:jbruno at unc.edu>

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