Correction to Grist/TNC piece on coral bleaching

In a Grist repost of a TNC interview with Joanne Wilson, Robert Lalasz asks:

You found less coral bleaching on this expedition than you’d thought you would. How significant is that finding? Should we be less worried about coral bleaching than we were before?

Joanne Wilson: Coral bleaching occurs when water temperatures are warmer than normal — for example, during La Niña events like the one we experienced last year. The increasing frequency and intensity of these warming events is associated with climate change. Fortunately, during our expedition, water temperatures were within normal ranges, so corals on Misool reefs were not bleaching. But with bleaching events predicted to increase in the future, we are still vigilant and concerned about Raja Ampat’s reefs.

Wrong answer!  Mass coral bleaching is indeed often coincident with the El Nino phase of ENSO, but it now seems quite clear that this is because of elevated background  Sea Surface Temperature (driven by Anthropogenic Climate Change). El Nino events have not become more frequent or severe nor are they expected to in the 21st century due to ACC or any other factor, human or natural.

In fact, it is only a matter of time before we start seeing mass-bleaching during La Nina, as SST in that phase gets progressively warmer.  In fact 2011 is expected to be the warmest “La Nina year” (I don’t like this terminology) on record and will be warmer than “El Nino years” of the recent past:

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