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

Dr. C. Mark Eakin Mark.Eakin at noaa.gov
Thu Sep 23 05:17:56 EDT 2010


I agree with you that it would have been more accurate if the article had said that there was an El Nino during 2009-2010, rather than using the phrase "2010 is also an El Niño year". The reality is that El Nino (and La Nina) just don't respect the Julian calendar. It would be much easier if they would just start and end within a single calendar year. Unfortunately, they don't and it confuses many people. They are events that generally last less than 12 months but span two calendar years. 

Many people refer to 1998 as an El Nino year. 2010 is really no different in terms of this terminology. Both are the second year of an El Nino. Both may also be the first year of a La Nina but we will have to wait to see if the forecasts are correct. 

What are the differences between 1997-1999 and 2009-2011? Firstly, the 1997-98 El Nino was much stronger. However, I recommend that you plot the tropical SST data such as those in the Nino 3.4 (the region of the tropical Pacific most commonly used for prediction and comparison of predictions to data: http://www.cpc.noaa.gov/data/indices/). If you do, you will see that although 1997-98 was a much stronger El Nino, it only exceeded 27°C for about 3 weeks longer than 2009-2010. Secondly, the 2010-2011 La Nina that still seems to be building has been quite comparable to the 1998-99 La Nina up to and during September 1998.

You are also right that we are seeing warming in many reef areas. This was also the story in 1998 during that El Nino-La Nina transition. This, in fact led to much of the bleaching we saw at that time. The warming in the Caribbean during 1997-1998 was highest in 1998 just as it is now (second year of an El Nino) and this pattern has been driven by Pacific-Caribbean teleconnections that have been in place since late 2009. Other areas that warm during La Nina are warming now as well. Reefs really suffer when a La Nina follows immediately on the heels of an El Nino. That is why we should be so concerned about this year.

I do agree that attribution of what is going on this year to an ENSO transition does not make as strong a case for anthropogenic climate change (ACC) as if this were a non-ENSO period. However, I think it is most important to properly identify the climatological conditions that exist and recognize the impact \ they are likely to have on coral reefs. As scientists, whether the current conditions strengthen the case for ACC or not should not influence our characterization of the event. I think we have to be rigorous about our scientific approach without adding "spin" to the science to make a case for ACC.

If you or others would like to learn more about El Nino, La Nina, their timing, strength, dynamics, and impacts, I recommend starting with the NOAA El Nino page (or a page from another prominent weather/climate agency):

After that, I recommend reading some of the papers from the references. The McPhaden paper is an excellent, quick start. The Philander book is even better if you really want to learn the basics. From there, many authors have continued the work to look into various patterns, discussions of the different "flavors" of El Ninos (Central Pacific, Eastern Pacific, El Nino "modoki", etc.). It quickly becomes apparent that El Ninos and La Ninas are like snowflakes: no two are alike. At that point, it is time to deal with how ACC may influence ENSO variability and intensity and the patterns that develop when ENSO is superimposed upon ACC as is occurring now.



On Sep 22, 2010, at 4:22 PM, Bruno, John F wrote:

> 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.  
> John

C. Mark Eakin, Ph.D.
Coordinator, NOAA Coral Reef Watch
National Oceanic and Atmospheric Administration
Center for Satellite Applications and Research
Satellite Oceanography & Climate Division
e-mail: mark.eakin at noaa.gov
url: coralreefwatch.noaa.gov

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