[Coral-List] NY Times: Extreme Heat Puts Coral Reefs at Risk

Bruno, John F jbruno at unc.edu
Wed Sep 22 22:22:01 EDT 2010

Hi Mark,

> Actually, John, it merely shows that they did not refer to it properly as the El Nino of 2009-10. Because El Nino events span two years, 2010 is an El Nino year in the same way that 1998 was: year 2 of an El Nino event. Also like 1998, it is the first year of what we expect to be a significant La Nina. If it holds, it will be the 2010-2011 La Nina.

No, I think this may mean more than that.  I am not quibbling about semantics.  If you think it makes sense to label 2010 an El Nino year when we've been in La Nina since May, well that's your prerogative.  My point is that we are in a La Nina and yet we are still seeing very significant large scale warming in several regions including two or three tropical reef regions.  I think this is significant.  

To get more technical about it, the negative temp. anomalies for both SST and subsurface temp. across the eastern and central equatorial Pacific have been running 1.5 to 2 C cool for 3-4 months and yet as you have pointed out to us all, there are concurrent high temp. anomalies (1-2 C) in the western Pacific (coral triangle region), Caribbean and S. Central Pacific, despite the presence of a range of La Nina indicators.  I think this is noteworthy.  First, because this is what Ove H-G and others have been predicting was going to happen (more frequent large scale events even during non-El Nino phases).  Second, because it strengthens the case for attributing such tropical warming and mass bleaching to anthropogenic greenhouse gas emissions.  Such attribution was/is difficult if the mass bleaching only takes place during El Nino.  We all know the two arguments for making such attribution to 95, 98 and 05 were that (a) Anthropogenic Climate Change (ACC) has increased the intensity of El Nino and (b) that ACC raised the background temperature so that El Nino high temp. anomalies are that much higher.  Both explanations are plausible and are not mutually exclusive, however, (a) is problematic because the theory does not clearly support the expectation that ACC will intensify ENSO and because there has not been an obvious increase in ENSO intensity (but please note I am not rejecting this hypothesis) and (b) is weakened by the fact that we don't and can't know how high the recent El Nino highs would have been in the absence of ACC.  

I am arguing this is a significant event for our community as it substantially increases our confidence* in attributing mass coral bleaching to ACC (believe me, such rigorous quantitative attribution is very difficult).  In other words, skeptics can no longer say "it's just the natural ENSO cycle" which they frequently do.  Hypothesis (b) indeed predicts that we will eventually start seeing ecologically significant high anomalies even during La Nina, which we are.  Get it now?! 

*or at least it will if it all plays out as expected; we will know in a month or two.  

> There is strong statistical evidence and a physical basis that the Caribbean normally warms in the second year of El Nino events.

Don't confuse the second El Nino summer of a two El Nino summer ENSO with the La Nina summer following an El Nino. I.e., your point doesn't apply to the situation we have now.  The El Nino is long gone and we are in La Nina.  By your argument, we would have seen warming/mass bleaching during 1996, 1999 and 2006: we obviously didn't.  During all three of those events, the major warming and bleaching happened during the El Nino summer, not during the following La Nina summer.  Think about 98: the northern hemisphere mass bleaching mostly took place during the northern hemisphere summer (~ July - Oct) when we were still in El Nino, and not 4 or 5 months into the following La Nina or in July - Oct  99.  Likewise on the GBR, the mass bleaching was in March/April 98 not March/April 99 (~ 5-6 months into the La Nina).  

Instead of going to the new coral reef curmudgeon site, maybe we can continue this on facebook:)

BTW, I really enjoyed your excellent and very informative webcast on all this.   

With love and respect.  


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