Ocean acidification is independent of climate sensitivity, and it's another reason to be concerned about the unprecedented rapidity of our CO2 emissions.
Lonny Eachus also linked to that misinformation from Matt Ridley, a journalist with a long history of distorting climate science.
In contrast, I quoted from Honisch et al. 2012 (PDF), Knoll et al. 2007 (PDF), and Ken Caldeira’s 2012 AGU lecture. That last link was from my videos section which also includes:
I'm not a chemist or a marine biologist/ecologist, so I read peer-reviewed papers and go to conferences like the AGU to watch lectures by scientists who do specialize and publish in those fields. For instance, consider that 2011 AGU panel on declining reef health. Nina Keul observed one species of foramanifera Glas et al. 2012 (PDF) growing faster as carbonate ion concentration decreases (which happens when CO2 increases). She provided context by noting that this is one species from one experiment, noting that this is like looking at one puzzle piece of a big puzzle.
Then Adina Paytan provides further context by noting that most species aren't like this. She shows Fig. 2 from Crook et al. 2012 (PDF) which shows that only ~3 out of 9 species of coral are present in locations with naturally low pH and notes that "Because these three species are rarely major contributors to Caribbean reef framework, these data may indicate that today’s more complex frame-building species may be replaced by smaller, possibly patchy, colonies of only a few species along the Mesoamerican Barrier Reef."
Finally, Robert Riding provides a paleo perspective. Note that he admitted a mistake during questions. Contrast this with Matt Ridley's misinformation which repeats many arguments scientists had already tried to correct. Instead of correcting his mistakes, Ridley just recycled the same talking points propped up with different studies.
For instance, Ridley vaguely refers to Jury et al. 2010 (PDF). Ridley and others wrongly imply that Jury et al. 2010 shows that corals in general and other species build their shells using bicarbonate (HCO3-) instead of carbonate (CO_3^2-).
In reality, after a long list of studies, Jury et al. 2010 says "While the studies above show drastic reductions in coral calcification in response to ocean acidification, there are indications that such responses are not ubiquitous."
So Jury et al. 2010 acknowledges that most coral species show drastic calcification reduction, and simply notes that some species don't. So Jury et al. 2010 is consistent with that 2011 AGU panel, which also showed that most (but not all) species of coral are sensitive to the reduced carbonate concentrations caused by our CO2 emissions (i.e. ocean acidification). It's also consistent with Comeau et al. 2012: "[CO_3^2-] played a significant role in light and dark calcification of P. rus, whereas [HCO3-] mainly affected calcification in the light. Both [CO_3^2-] and [HCO3-] had a significant effect on the calcification of H. onkodes, but the strongest relationship was found with [CO_3^2-]."
Chris Langdon had even previously told Matt Ridley: "Empirical studies have shown that many calcifying organisms, including corals, only use CO_3^2- (carbonate) to build their skeletons. The HCO3-, while, 7-times more abundant than the CO_3^2-, does not seem to be available for calcification. A drop in pH from 8.1 to 7.8 has been shown to reduce the ability of many species of coral to build their skeletons by 30 to 40 per cent. This same small reduction in pH has been shown to adversely affect coral reproduction as well by decreasing larval settlement success and post-settlement growth of the juvenile coral. Matt is correct that the skeleton and shell building of some species is unaffected or even increases under reduced pH. However, there is no free lunch. The reduction in pH makes it thermodynamically more difficult to precipitate calcium carbonate. While an organism can chose to overcome the increased expense of producing their skeleton or shell, it generally comes at a cost because less energy is now available for some other life process. Loss of muscle mass in some invertebrates and a reduced growth rate in the case of a coccolithophorid are examples of the tradeoffs that some species have made."
Fabricius et al. 2011 (PDF): Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations
"Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms[1,2,3,4]. However, few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems[5,6,7]. Here we show that as pH declines from 8.1 to 7.8 (the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750 ppm, consistent with some scenarios for the end of this century) some organisms benefit, but many more lose out. We investigated coral reefs, seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea. At reduced pH, we observed reductions in coral diversity, recruitment and abundances of structurally complex framework builders, and shifts in competitive interactions between taxa. However, coral cover remained constant between pH 8.1 and ~7.8, because massive Porites corals established dominance over structural corals, despite low rates of calcification. Reef development ceased below pH 7.7. Our empirical data from this unique field setting confirm model predictions that ocean acidification, together with temperature stress, will probably lead to severely reduced diversity, structural complexity and resilience of Indo-Pacific coral reefs within this century."
Pandolfi et al. 2011 (PDF): Projecting Coral Reef Futures Under Global Warming and Ocean Acidification
"Many physiological responses in present-day coral reefs to climate change are interpreted as consistent with the imminent disappearance of modern reefs globally because of annual mass bleaching events, carbonate dissolution, and insufficient time for substantial evolutionary responses. Emerging evidence for variability in the coral calcification response to acidification, geographical variation in bleaching susceptibility and recovery, responses to past climate change, and potential rates of adaptation to rapid warming supports an alternative scenario in which reef degradation occurs with greater temporal and spatial heterogeneity than current projections suggest. Reducing uncertainty in projecting coral reef futures requires improved understanding of past responses to rapid climate change; physiological responses to interacting factors, such as temperature, acidification, and nutrients; and the costs and constraints imposed by acclimation and adaptation."
IPCC Breakout Group I-2: Reconciling apparently contradictory observations
"This Breakout Group report summarizes participant discussions on divergent observations of the effects of ocean acidification for marine organisms. For calcification in zooxanthellate corals and in plankton, as well as for other processes, the Breakout Group considered examples of contradictory observations, the level of disagreement among data sets, and possible explanations for apparently conflicting results. From this evaluation, the Breakout Group investigated the complexity and species-specific nature of the coral calcification response to ocean acidification, the importance of clarifying present uncertainty about the responses of coccolithophores to ocean acidification, and the large inherent variability in the effects of ocean acidification for other processes considered."
McCulloch et al. 2012 (PDF): Coral resilience to ocean acidification and global warming through pH up-regulation
"Rapidly rising levels of atmospheric CO2 are not only causing ocean warming, but also lowering seawater pH hence the carbonate saturation state of the oceans, on which many marine organisms depend to calcify their skeletons[1,2]. Using boron isotope systematics, we show how scleractinian corals up-regulate pH at their site of calcification such that internal changes are approximately one-half of those in ambient seawater. This species-dependent pH-buffering capacity enables aragonitic corals to raise the saturation state of their calcifying medium, thereby increasing calcification rates at little additional energy cost. Using a model of pH regulation combined with abiotic calcification, we show that the enhanced kinetics of calcification owing to higher temperatures has the potential to counter the effects of ocean acidification. Up-regulation of pH, however, is not ubiquitous among calcifying organisms; those lacking this ability are likely to undergo severe declines in calcification as CO2 levels increase. The capacity to up-regulate pH is thus central to the resilience of calcifiers to ocean acidification, although the fate of zooxanthellate corals ultimately depends on the ability of both the photosymbionts and coral host to adapt to rapidly increasing ocean temperatures."
So Ridley was told that even though some species are tolerant to lower pH, most aren't. Ridley then cites Hendriks et al. 2010 (PDF) claiming "there was no significant mean effect" from lower pH in 372 studies of 44 marine species. But if the Hendriks et al. 2010 meta-study were inadvertently biased towards studies of the few tolerant species, they'd cancel the more numerous vulnerable species. Averages across seasons can also mask vulnerabilities, as in Rosa et al. 2013 which showed different impacts in summer and winter. Here's another problem:
Dupont et al. 2010 (PDF): What meta-analysis can tell us about vulnerability of marine biodiversity to ocean acidification?
"Ocean acidification has been proposed as a major threat for marine biodiversity. Hendriks et al. ... proposed an alternative view and suggested, based on a meta-analysis, that marine biota may be far more resistant to ocean acidification than hitherto believed. However, such a meta-analytical approach can mask more subtle features, for example differing sensitivities during the life-cycle of an organism. Using a similar metric on an echinoderm database, we show that key bottlenecks present in the life-cycle (e.g. larvae being more vulnerable than adults) and responsible for driving the whole species response may be hidden in a global meta-analysis. Our data illustrate that any ecological meta-analysis should be hypothesis driven, taking into account the complexity of biological systems, including all life-cycle stages and key biological processes. Available data allow us to conclude that near-future ocean acidification can/will have dramatic negative impact on some marine species, including echinoderms, with likely consequences at the ecosystem level."
Hendriks and Duarte's reply (PDF) includes: "... Conveying scientific evidence along with an open acknowledgment of uncertainties to help separate evidence from judgment should not harm the need to act to mitigate ocean acidification and should pave the road for robust progress in our understanding of how ocean acidification impacts biota of the ocean."
Other papers have explored bottlenecks in early development:
Melzner et al. 2009 (PDF): Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny?
"Future ocean acidification has the potential to adversely affect many marine organisms. A growing body of evidence suggests that many species could suffer from reduced fertilization success, decreases in larval- and adult growth rates, reduced calcification rates, and even mortality when being exposed to near-future levels (year 2100 scenarios) of ocean acidification. Little research focus is currently placed on those organisms/taxa that might be less vulnerable to the anticipated changes in ocean chemistry; this is unfortunate, as the comparison of more vulnerable to more tolerant physiotypes could provide us with those physiological traits that are crucial for ecological success in a future ocean. Here, we attempt to summarize some ontogenetic and lifestyle traits that lead to an increased tolerance towards high environmental pCO2. ... while some of these taxa are adapted to cope with elevated pCO2 during their regular embryonic development, gametes, zygotes and early embryonic stages, which lack specialized ion-regulatory epithelia, may be the true bottleneck for ecological success – even of the more tolerant taxa. ..."
Albright 2011 (PDF): Reviewing the Effects of Ocean Acidification on Sexual Reproduction and Early Life History Stages of Reef-Building Corals
"The studies reviewed here demonstrate that ocean acidification has the potential to affect sexual reproduction and multiple early life history stages of corals that are critical to reef persistence and resilience. While further studies are essential, available information indicates that affected processes may include sperm motility and fertilization success, larval metabolism, larval settlement, and postsettlement growth and calcification. ... Although ocean acidification is now recognized as a substantial threat to marine calcifiers and their ability to secrete calcium carbonate shells and/or skeletons, the studies reviewed here demonstrate that increasing pCO2 has the potential to impact multiple life history stages of corals, including critical processes independent of calcification. ... Negative impacts on successive life history stages may cumulate in such a way that the overall effect on recruitment is severe. For example, results of studies conducted with the threatened Caribbean elkhorn coral, Acropora palmata, indicate that ocean acidification has the potential to reduce fertilization success by 12-13% (averaged across all sperm concentrations) and to decrease settlement success by 45–69% at pCO2 concentrations expected for the middle and end of this century. The compounding effect of ocean acidification on these early life history stages translates into a 52–73% reduction in the number of larval settlers on the reef. The net impact on recruitment will likely be even greater, given that depressed postsettlement growth may translate into elevated rates of postsettlement mortality . ..."
This is how scientists learn about research outside of their own fields. Contrast that with Lonny Eachus, who later linked to and retweeted more of Ridley's misinformation where Ridley ignored Tamsin Edwards and other scientists who tried to correct his obvious error. Ridley also advertised a flawed paper by Prof. Richard Tol, who also has problems admitting his mistakes. Instead, anyone interested in ocean acidification should read the peer-reviewed literature and/or watch freely available lectures from scientists who publish in that field.
Regarding other comments, I've repeatedly noted that the PETM's rapid warming stressed ecosystems. So it's not goalpost moving to note that rapid GHG emissions cause rapid warming and ocean acidification, and that these both stress ecosystems. In fact, only a Sky Dragon Slayer would argue that rapidly increasing CO2 wouldn't cause rapid warming, and only someone unfamiliar with past extinctions would argue that rapid warming wouldn't stress ecosystems. Lectures about CO2 vs. methane also aren't necessary; I've noted: The PETM happened ~55 million years ago, and was a rapid spike of about 5C warming over about 200,000 years. It’s not clear if CO2 or CH4 caused the distinct warming and carbon isotope excursion spikes, but it’s clear that ocean outgassing can’t explain the carbon isotope excursion spike:
"Atmospheric pCO2 increases from 834 ppm to either 1,500 ppm (CH4 scenario) or 4,200 ppm (Corg scenario) during the main phase of the PETM (Fig. 4d). The corresponding global ocean surface temperature increase during the peak PETM is 2.1C (CH4 scenario) and 6.5C (Corg scenario) respectively. (Fig. 4e)."
This PETM CO2/methane debate is genuine, unlike many baseless claims. For instance, I asked for citations of PETM warming not due to GHG like CO2/methane because of mistaken claims it was due to H2O and/or volcanoes heating the oceans. Let's explore the literature...
Thomas and Shackleton 1996 (PDF): The Paleocene-Eocene benthic foraminiferal extinction and stable isotope anomalies
"In the late Paleocene to early Eocene, deep sea benthic foraminifera suffered their only global extinction of the last 75 million years and diversity decreased worldwide by 30-50% in a few thousand years. At Maud Rise (Weddell Sea, Antarctica; Sites 689 and 690, palaeodepths 1100 m and 1900 m) and Walvis Ridge (Southeastern Atlantic, Sites 525 and 527, palaeodepths 1600 m and 3400 m) post-extinction faunas were low-diversity and high-dominance, but the dominant species differed by geographical location. ... The species-richness remained very low for about 50,000 years, then gradually increased. The extinction was synchronous with a large, negative, short-term excursion of carbon and oxygen isotopes in planktonic and benthic foraminifera and bulk carbonate. The isotope excursions reached peak negative values in a few thousand years and values returned to pre-excursion levels in about 50,000 years. ... The oxygen isotope excursion was about -1.5%o for benthic foraminifera at Walvis Ridge and Maud Rise, -1%o for planktonic foraminifera at Maud Rise. The rapid oxygen isotope excursion at a time when polar ice-sheets were absent or insignificant can be explained by an increase in temperature by 4-6C of high latitude surface waters and deep waters world wide. ..."
Scheibnera and Speijerb 2008 (PDF): Late Paleocene–early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change
"... The onset of the latter prominent larger foraminifera-dominated platform correlates with the Paleocene/Eocene Thermal Maximum. The causes for the change from coral-dominated platforms to larger foraminifera-dominated platforms are multilayered. The decline of coralgal reefs in low latitudes during platform stage II is related to overall warming, leading to sea-surface temperatures in the tropics beyond the maximum temperature range of corals. The overall low occurrence of coral reefs in the Paleogene might be related to the presence of a calcite sea. At the same time larger foraminifera started to flourish after their near extinction at the Cretaceous/Paleogene boundary. The demise of coralgal reefs at all studied paleolatitudes in platform stage III can be founded on the effects of the PETM, resulting in short-term warming, eutrophic conditions on the shelves and acidification of the oceans, hampering the growth of aragonitic corals, while calcitic larger foraminifera flourished. In the absence of other successful carbonate-producing organisms, larger foraminifera were able to take over the role as the dominant carbonate platform inhabitant, leading to a stepwise Tethyan platform stage evolution around the Paleocene/Eocene boundary. This szenario might be also effective for threatened coral reef sites."
Payne and Clapham 2012 (PDF): End-Permian Mass Extinction in the Oceans: An Ancient Analog for the Twenty-First Century?
"The greatest loss of biodiversity in the history of animal life occurred at the end of the Permian Period (~252 million years ago). This biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of Earth's largest continental flood basalt provinces, the Siberian Traps. Volatile release from basaltic magma and sedimentary strata during emplacement of the Siberian Traps can account for most end-Permian paleontological and geochemical observations. Climate change and, perhaps, destruction of the ozone layer can explain extinctions on land, whereas changes in ocean oxygen levels, CO2, pH, and temperature can account for extinction selectivity across marine animals. These emerging insights from geology, geochemistry, and paleobiology suggest that the end-Permian extinction may serve as an important ancient analog for twenty-first century oceans."
Kiessling and Simpson 2010: On the potential for ocean acidification to be a general cause of ancient reef crises
"Anthropogenic rise in the carbon dioxide concentration in the atmosphere leads to global warming and acidification of the oceans. Ocean acidification (OA) is harmful to many organisms but especially to those that build massive skeletons of calcium carbonate, such as reef corals. Here, we test the recent suggestion that OA leads not only to declining calcification of reef corals and reduced growth rates of reefs but may also have been a trigger of ancient reef crises and mass extinctions in the sea. We analyse the fossil record of biogenic reefs and marine organisms to (1) assess the timing and intensity of ancient reef crises, (2) check which reef crises were concurrent with inferred pulses of carbon dioxide concentrations and (3) evaluate the correlation between reef crises and mass extinctions and their selectivity in terms of inferred physiological buffering. We conclude that four of five global metazoan reef crises in the last 500 Myr were probably at least partially governed by OA and rapid global warming. However, only two of the big five mass extinctions show geological evidence of OA."
Since Ridley also seems to think that rapid pH swings make coral insensitive to ocean acidification, it's worth pointing out that these rapid swings have been happening since the oceans formed. But they didn't prevent past instances of ocean acidification from stressing ecosystems. Here's more modern research:
Okazaki 2013: Stress-tolerant corals of Florida Bay are vulnerable to ocean acidification
"In situ calcification measurements tested the hypothesis that corals from environments (Florida Bay, USA) that naturally experience large swings in pCO2 and pH will be tolerant or less sensitive to ocean acidification than species from laboratory experiments with less variable carbonate chemistry. The pCO2 in Florida Bay varies from summer to winter by several hundred ppm roughly comparable to the increase predicted by the end of the century. Rates of net photosynthesis and calcification of two stress-tolerant coral species, Siderastrea radians and Solenastrea hyades, were measured under the prevailing ambient chemical conditions and under conditions amended to simulate a pH drop of 0.1–0.2 units at bimonthly intervals over a 2-yr period. Net photosynthesis was not changed by the elevation in pCO2 and drop in pH; however, calcification declined by 52 and 50 % per unit decrease in saturation state, respectively. These results indicate that the calcification rates of S. radians and S. hyades are just as sensitive to a reduction in saturation state as coral species that have been previously studied. In other words, stress tolerance to temperature and salinity extremes as well as regular exposure to large swings in pCO2 and pH did not make them any less sensitive to ocean acidification. These two species likely survive in Florida Bay in part because they devote proportionately less energy to calcification than most other species and the average saturation state is elevated relative to that of nearby offshore water due to high rates of primary production by seagrasses."
Finally, calcification isn't everything. Hamilton et al. 2013 shows that ocean acidification increases fish anxiety, and Simpson et al. 2011 (PDF) shows that it erodes crucial auditory behaviour in a marine fish. Munday et al. 2014 shows that fish stop avoiding predator odor, possibly because of the added stress of using bicarbonate in lower pH waters. Naturally, this doesn't work out well. A billion people depend on seafood.