I am prompted to write this post following a long and somewhat fractious conversation at Ken Rice’s blog, ATTP, in response to a guest post by Geoff Price on coral reef bleaching. As the post referred to me personally and to a blog post I wrote on Cliscep over a year ago, I decided, against my better judgement, to comment. This current essay is written as a kind of formal response to some of the less obnoxious comments on that thread at ATTP – and a few of the more obnoxious ones. It is also written as a kind of follow up to my original post on coral bleaching and my recent post on the 1876-78 super El Nino. Coral bleaching, as you may know, is still a very contentious issue ‘out there’ and has cost James Cook University professor, Peter Ridd, his job for having the audacity to question accepted wisdom that climate change was destroying the Great Barrier Reef. Ridd has raised funds to legally contest his dismissal and the case is set for 26-28 March. I wish him well.
My argument, which the denizens at ATTP steadfastly refused to grasp in its utter simplicity, expressed on that thread and in my original blog post, was that the series of mass and global coral bleaching events since the early ’80s were caused primarily by the occurrence of three super El Ninos (plus lesser ones in between) between 1982 and 2016 and not by the long term secular global warming trend since 1850. The study which I criticised in my coral bleaching article, published in 2018, authored by Hughes et al, manifestly points the finger of blame at global warming for mass coral bleaching events since 1980:
Coral bleaching occurs when stressful conditions result in the expulsion of the algal partner from the coral. Before anthropogenic climate warming, such events were relatively rare, allowing for recovery of the reef between events.
Tropical reef systems are transitioning to a new era in which the interval between recurrent bouts of coral bleaching is too short for a full recovery of mature assemblages.
As global warming has progressed, tropical sea surface temperatures are warmer now during current La Niña conditions than they were during El Niño events three decades ago. Consequently, as we transition to the Anthropocene, coral bleaching is occurring more frequently in all El Niño–Southern Oscillation phases, increasing the likelihood of annual bleaching in the coming decades.
Let’s look at that specific claim: As global warming has progressed, tropical sea surface temperatures are warmer now during current La Niña conditions than they were during El Niño events three decades ago. Here’s a graph of monthly tropical SSTs from 1979 to January 2019 according to data compiled by NOAA (solid line is running 37 month average):
The paper was published in January 2018, so one presumes by ‘current La Nina conditions’ they meant the modest La Nina conditions which prevailed at that time (the DJF Nino3.4 anomaly was -0.9C). You can clearly see the La Nina on the above graph, at the beginning of 2018. The tropics at the time were about -0.1C below the 1981-2010 mean. There were two El Ninos in the 1980s ‘three decades ago’ – 1982/83 and 1987/88. The tropics when they peaked were between 0.5C and 0.6C warmer than the 1981-2010 mean. This means that when El Ninos were in full swing during the 1980s, the tropics were warmer by about 0.6C-0.7C than they were during the early 2018 La Nina.
So it would appear that Hughes at al’s claim that current La Nina tropical SSTs are warmer than El Nino tropical SSTs three decades ago is bullshit. It just isn’t so. This false claim doesn’t exactly bode well for the quality of science on offer in the rest of the paper. But then neither does the comment that we are ‘transitioning into the Anthropocene’, on account of the fact that the Anthropocene is not an officially recognised geological epoch and that we transitioned into the Meghalayan stage of the Holocene geological epoch some 4200 years ago and are still there.
You don’t have to read much further to uncover the next instance of bullshit in this ‘scientific’ paper:
The average surface temperature of Earth has risen by close to 1°C as of the 1880s (1), and global temperatures in 2015 and 2016 were the warmest since instrumental record keeping began in the 19th century (2). Recurrent regional-scale (>1000 km) bleaching and mortality of corals is a modern phenomenon caused by anthropogenic global warming (3–10).
That statement is unequivocal by the authors: Recurrent regional-scale (>1000 km) bleaching and mortality of corals is a modern phenomenon caused by anthropogenic global warming (3–10). So naturally, I went to the two citations which presumably would demonstrate the veracity of this statement. Here is what I found:
The causes of small scale, isolated bleaching events can often be explained by particular stressors (e.g., temperature, salinity, light, sedimentation, aerial exposure and pollutants), but attempts to explain large scale bleaching events in terms of possible global change (e.g., greenhouse warming, increased UV radiation flux, deteriorating ecosystem health, or some combination of the above) have not been convincing.
This statement belies the certainty expressed by Hughes et al that modern mass bleaching is caused by global warming. The cited paper was published in 1993. I cited a study probably published in 1996 which actually demonstrated the point I was trying to make, rather than contradicted it (despite the risible efforts of ATTP’s clientele to prove otherwise) and was roundly criticised for doing so by commenters seemingly enamoured of Hughes et al. How odd. The next cited paper (published in 2010) is even better:
Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence.
Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid‐century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree‐heating‐months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors.
Noting that we may have lurkers from the depths of ATTP’s poisoned well (courtesy of yours truly according to the Williard) on this page, I shall re-iterate very clearly the significance of the above quoted passage for the benefit of those readers who may be lacking in the English comprehension department:
Hughes et al cited a study which should affirm their conclusion that global warming is causing mass bleaching events after 1980. It doesn’t. It directly contradicts that assessment in the case of of the Mesoamerican reef, which is the subject of the study, by noting that waters were warmer during the mid 20th century and the principal cause of mass bleaching in 1998 was reduced tolerance to not unprecedented heat stress caused by chronic local stressors related to the human population.
Oh dear. On ATTP, I presented an essay which makes exactly this point: that coral reef bleaching is a complex process and that there are many stressors involved. It’s just too simplistic to state that ‘global warming’ is making coral reefs disappear. Even if this is the case and the modest (I can use that term here without being accused of anthropocentrism – or anthropomorphism according to Steven Mosher) secular trend in tropical ocean warming is causing mass coral bleaching, it still cannot be viewed in isolation from local stressors. My personal opinion is that three successive super El Ninos since the beginning of the 1980’s (unprecedented in recent history) have contributed far more to mass coral bleaching than the secular global warming trend, but I shall discuss this in a follow up post, so as not to bombard readers with too much information on one post.