[Coral-List] Evidence that ocean warming has caused most Caribbean coral loss

Bruno, John jbruno at unc.edu
Tue May 2 11:40:44 EDT 2017

Dear Ulf,

My understanding is that the current, human-caused warming is happening 10-100X more rapidly than has occurred over the last 65 million years during natural warming events (Diffenbaugh 2013). The greater rate is obviously a reason we expect greater impacts to species and ecosystems than we’ve seen in the past.

You might be right that in the near-term (this century), we are not likely to lose many coral species to extinction. However, if warming trends follow RCP 8.5 and reefs warm by another 3 C by 2100 (as the climate models predict), it is very likely that a substantial portion of reef taxa couldn’t tolerate summertime temps of 33-35 C. Some would migrate to higher latitudes, but many probably couldn’t (for a variety of reasons). And in following centuries, if warming continued, we’d lose more than reefs - most tropical marine biodiversity would be lost. But even in the near-term, losing the reefs is a big problem for people! You seem rather blasé about that.


If you continue to deny reality, there really is no changing your mind. As most coral-listers know, and as 97% of climate scientists agree, the predicted dramatic warming is indeed already happening. Over the last 30-40 years, the oceans have been warming at ~0.13 C per decade. Have a look at the ocean heat content map in my post (also see Gleckler et al 2016). Chollett et al 2012 found that the Caribbean warming rate from 1985 to 2009 was 0.27 °C / decade􏰀. Both geologically and physiologically, that is a pretty dramatic rate and degree of warming for a tropical marine ecosystem.

That fact, combined with the extensive evidence of warming impacts on corals and reef ecosystems across the Caribbean (xxx), and indeed globally, clearly refutes the nonsense you and Mike are peddling (which is all regurgitation from the standard climate change denial websites like CO2 Science) that “THE ONLY REASONABLE EXPLANATION IS POLLUTION”.

As we all know, if it were only pollution, all the science on bleaching and temperature impacts wouldn’t exist (but it does) and isolated reefs, far from pollution sources would be “healthier” (but they aren’t). Reefs around the world isolated from pollution have lost just as much coral cover - obviously you can’t blame that on local people (they’re aren’t any!). That’s on us.

Aside from this spatial pattern, Mike Risk’s follow-up argument that "the only logical explanation for the present decline in coral reefs is that of widespread pollution-"pollution” is only logical if one denies that ocean warming is already happening, e.g., if your’e unaware that the Caribbean has already warmed by at least 1C.

Chollett I, Müller-Karger FE, Heron SF, Skirving W, Mumby PJ. Seasonal and spatial heterogeneity of recent sea surface temperature trends in the Caribbean Sea and southeast Gulf of Mexico. Mar Pollut Bull. March 2012. doi:10.1016/j.marpolbul.2012.02.016.

Diffenbaugh, N. S. & Field, C. B. Changes in Ecologically Critical Terrestrial Climate Conditions. Science 341, 486 (2013).

Gleckler PJ, Durack PJ, Stouffer RJ, Johnson GC, Forest CE. Industrial-era global ocean heat uptake doubles in recent decades. Nat Clim Chang. 2016;6(4):394-398. http://dx.doi.org/10.1038/nclimate2915


John Francis Bruno
Professor, Dept of Biology
UNC Chapel Hill

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