by Judith Curry
Today the surface ocean is almost 30% more acidic than it was in pre-industrial times, and over the next few decades, the level of acidity of the surface ocean will continue to rise without deliberate action to reduce carbon dioxide emissions. Increasingly this will cause major problems for many marine organisms like shellfish and corals. – Scott Doney
Numerous people have asked me to do a post on ocean acidification; I haven’t done this since I don’t have much expertise on this. Scott Doney’s recent congressional testimony provides the impetus for this post.
Scott Doney’s testimony
Excerpts from Doney’s recent congressional testimony [link]:
The ocean takes up roughly one quarter of human emissions to the atmosphere of carbon dioxide from fossil fuel burning and deforestation. Additional carbon dioxide uptake causes direct changes in seawater acid-base and inorganic carbon chemistry in a process termed ocean acidification. Acidification is independent of warming of the atmosphere but the two are linked through the underlying cause of elevated atmospheric carbon dioxide. Growing evidence suggests that ocean acidification will strongly impact many types of marine organisms, from microscopic plankton to shellfish and corals.
Acidification and climate change will put further pressure on living marine resources, such as fisheries and coral reefs that we depend upon for food, tourism and other economic and aesthetic benefits. Scientific observations show that ocean acidification is already occurring around the globe and is amplified in some coastal regions by changing ocean circulation, pollution, and land management practices. Recent near collapses of the oyster fishery in the Pacific Northwest, directly attributed to changing seawater chemistry, had substantial negative impacts on local jobs and economies.
We have an opportunity now to limit the negative impact of ocean acidification in the future. Key elements include curbing human carbon dioxide emissions to the atmosphere, improved control of local pollution sources, reducing coastal habitat destruction, and better preparing coastal human communities to withstand the amount of ocean acidification and climate change that is unavoidable. At the State and local level, adaptation and mitigation strategies are being developed for ocean acidification.
Doney’s testimony includes the following topic sections:
- Social and economic impacts of ocean acidification
- Ocean and global carbon cycle
- Ocean acidification and changing seawater chemistry
- Adaptation and mitigation strategies
Below is some text from the sections on Ocean and global carbon cycle that explains the basic mechanism:
The ocean uptake of excess atmospheric carbon dioxide, the excess above preindustrial levels driven by human emissions, causes well-understood and substantial changes in seawater chemistry that can affect marine organisms and ecosystems. Carbon dioxide (CO2) acts as a weak acid when added to seawater leading to the release of hydrogen ions (H+) and bicarbonate (HCO3-) ions.
The reaction increases seawater acidity and increases the hydrogen ion activity, thus lowering seawater pH. pH is defined as the negative logarithm of the hydrogen ion activity, so that a 1-unit change in pH is equivalent to a 10-fold change in H+. Most of the extra hydrogen ions react with carbonate ions (CO3 2-) and lower their ambient concentrations.
This second reaction is important because reduced seawater carbonate ion concentrations decrease the saturation levels of calcium carbonate (CaCO3), a hard mineral used by many marine microbes, plants and animals to form shells and skeletons. Many organisms require supersaturated conditions to form sufficient calcium carbonate shells or skeletons, and biological calcification rates tend to decrease in response to lower carbonate ion concentrations, even when the ambient seawater is still supersaturated.
Long-term ocean acidification trends are clearly evident over the past several decades in open-ocean time-series and hydrographic survey data, and the trends are consistent with the growth rate of atmospheric carbon dioxide (Dore et al., 2009). From preindustrial levels, contemporary surface ocean pH is estimated to have dropped on average from 8.2 to 8.1, or by about 0.1 pH units (a 26% increase in hydrogen ion concentration), and further decreases of 0.22 to 0.35 pH units are projected over this century unless carbon dioxide emissions are significantly reduced.
Global upper-ocean chemistry trends driven by human carbon dioxide emissions are more rapid than variations in the geological past. For example, atmospheric carbon dioxide grew by approximately 30% during the transition from the most recent cold glacial period, about 20,000 years ago, to the current warm interglacial period; the corresponding rate of decrease in surface ocean pH, driven by geological processes, was approximately 50 times slower than the current rate driven largely by fossil fuel burning. Many marine organisms appear to be physiologically adapted to relatively constant local acid-base conditions and are sensitive to relatively small variations in pH and the saturation state of calcium carbonate.
Present-day ocean surface waters are supersaturated for the major carbonate mineral forms used by marine organisms, including the more soluble form aragonite (corals, many mollusks) and the less soluble form calcite (coccolithophores, foraminifera, and some mollusks). However, calcium carbonate saturation states of both mineral forms are declining everywhere. Polar oceans are of particular concern because cold surface waters naturally hold more carbon dioxide and started off with lower calcium carbonate saturation states. Model simulations indicate that polar surface waters will become undersaturated for aragonite in the near future for the Arctic (atmospheric carbon dioxide of 400-450 ppm) and by mid-century for the southern ocean off the Antarctic (atmospheric carbon dioxide of 550-600 ppm). This is expected to result in major changes in polar ecosystems.
Other ocean regions also may be more susceptible to aragonite undersaturation because of elevated background levels of carbon dioxide. These include eastern boundary current upwelling systems such as those off the U.S. west coast along coastal California, Oregon and Washington, deep-sea and subsurface oxygen minimum zones, and coastal waters that are already experiencing excess nutrient levels (eutrophication) and low dissolved oxygen (hypoxia) due to human-driven nutrient pollution from land-based activities . Nutrient overloading near shore encourages algal growth that is consumed by microbes, using up dissolved oxygen and releasing even more carbon dioxide locally. Coastal, estuarine, and coral reef systems also experience high levels of temporal variability on diurnal to weekly time-scales, challenging both observational efforts and interpretations of biological experiments.
Scott Doney’s bio information:
My name is Scott Doney, and I am a Senior Scientist at the Woods Hole Oceanographic Institution in Woods Hole MA. My research focuses on interactions among climate, the ocean and global carbon cycles, and marine ecosystems, and I have published more than 200 peer-reviewed scientific journal articles and book chapters on these and related subjects. I have served on the U.S. Carbon Cycle Science Program Scientific Steering Group and the U.S. Community Climate System Model Scientific Steering Committee. I was the inaugural chair of the U.S. Ocean Carbon and Biogeochemistry (OCB) Program and am currently on the steering committees for the Ocean Carbon and Biogeochemistry Program and the U.S. CLIVAR/CO2 Repeat Hydrography Program. I am also a convening lead author for the Oceans and Marine Resources chapter of the U.S. 2013 National Climate Assessment.
Craig Idso has written comprehensive rebuttal to the NRDC film “Acid Test: The Global Challenge of Ocean Acidification.” [link]
So what’s the story here? Are coral reefs really in their last decades of existence? Will the shells of other calcifying marine life also dissolve away during our lifetimes? The NRDC film certainly makes it appear that such is the case; but a little scientific sleuthing reveals nothing of substance in this regard. In fact, even a cursory review of the peer-reviewed scientific literature reveals that an equally strong case – if not a more persuasive one – can be made for the proposition that the ongoing rise in atmospheric CO2 concentration will actually prove a boon to calcifying marine life. Sadly, however, the NRDC chose to present an extreme one-sided, propagandized view of ocean acidification; and in this critique we present the part of the story that they clearly don’t want you to know.
[25 pages of text, 13 pages of references]
From the Conclusions:
In conclusion, based on the many real-world observations and laboratory experiments described above, it is clear that recent theoretical claims of impending marine species extinctions, due to increases in the atmosphere’s CO2 concentration, have no basis in empirical reality. In fact, these unsupportable contentions are typically refuted by demonstrable facts. As such, the NRDC’s portrayal of CO2-induced ocean acidification as a megadisaster-in-the-making is seen, at best, to be a one-sided distortion of the truth or, at worst, a blatant attempt to deceive the public.
Surely, the NRDC and the scientists portrayed in their film should have been aware of at least one of the numerous peer-reviewed scientific journal articles that do not support a catastrophic – or even a problematic – view of the effect of ocean acidification on calcifying marine organisms; and they should have shared that information with the public. If by some slim chance they were not aware, shame on them for not investing the time, energy, and resources needed to fully investigate an issue that has profound significance for the biosphere. And if they did know the results of the studies we have discussed, no one should ever believe a single word they may utter or write in the future.
Finally, if there is a lesson to be learned from the materials presented in this document, it is that far too many predictions of CO2-induced catastrophes are looked upon as sure-to-occur, when real-world observations show such doomsday scenarios to be highly unlikely or even virtual impossibilities. The phenomenon of CO2-induced ocean acidification is no different. Rising atmospheric CO2 concentrations are not the bane of the biosphere; they are an invaluable boon to the planet’s many life forms.
JC comment: So whose view of the ocean acidification is correct: Doney’s or Idso’s? In this instance, it is instructive for me to describe my own reasoning process, since I come to this topic with very little first hand knowledge, beyond understanding the basic chemistry of the problem.
When I saw Scott Doney listed as a witness for this hearing, I was very pleased, since he is a scientific heavy hitter on this subject. However, upon reading the first page of his testimony, the following statement raised my skeptical hackles, especially since their was no evidence or reference to support this:
Today the surface ocean is almost 30% more acidic than it was in pre-industrial times.
I found Doney’s testimony to be highly normative, something that I am not a fan of in testimony by scientists. I did a word search, looking for ‘uncertain’, ‘disagreement’, ‘debate’, ‘unknown’. The only statements I found were:
Decisions should incorporate precautionary considerations to account for the fact that potential carbon dioxide thresholds are presently unknown for many aspects of ocean acidification.
The potential biological consequences due to acidification are slowly becoming clearer at the level of individual species, but substantial uncertainties remain particularly at the ecosystem level.
For these reasons, Doney’s testimony didn’t score too high on my credibility meter, in spite of my acknowledgement of his expertise and stature in the field.
I figured that there has to be another side to this story, so I did a quick google search and spotted Idso’s document. Idso’s document clearly states that there is another side to this story. Idso’s approach is more credible IMO, since he acknowledges that there are two sides to the story, that at this point may be equally plausible. I searched for the same 4 words; only spotted one use of ‘unknown’, so I am not sure how useful my little litmus test was.
The issue is this: failure of the ‘mainstream’ experts to adequately discuss uncertainty and alternative viewpoints leaves a void to be filled by the likes of Idso, with the inadvertent effect of elevating Idso’s essay more than it probably deserves.
That said, I cannot personally judge whether Doney’s or Idso’s arguments are better scientifically, without digging into the primary literature myself; and even then I am not sure how confident I would be in my own ability to assess this.
If we use the Italian Flag method (Michael Tobis will go ballistic if he spots this), we have:
- Evidence for (green): Doney’s arguments
- Evidence against (red): Idso’s arguments
- Uncertainty and ignorance (white): there must be plenty here, but I haven’t seen any document that articulates the known unknowns.
I suspect that red and white add up to more than 50%, that is as close as I can come to making an assessment on this.
I would appreciate any good references on this topic, and I look forward to your comments.
Update: I bring forward here some comments that I made in the thread that clarify my views on this:
Both Doney’s and Idso’s reports are normative. Both provide evidence. Did I say Idso was more convincing than Doney? No. But Idso scored some credibility points by stating that there is disagreement and debate, and actually presented the evidence for (at least in terms of the transcript of the NRDC film). Idso lost credibility points by having Monckton write the preface, which was rather over the top.
Credibility is product of expertise and trust. Doney scores much higher on expertise here. Personally I find it trust inspiring when a scientist acknowledges the existence of disagreement and debate, which is where Idso scored points
There is a 2010 NRC report on Ocean Acidification
Scott Doney was one of the authors of this report.
The money quotes re uncertainty:
“Ocean acidification research is in its infancy.”
“CONCLUSION: Present knowledge is insufficient to guide federal and state agencies in evaluating potential impacts for management purposes.”
I’m taking seriously the list of references (peer reviewed publications) that Idso supplies in his document. I am more interested in evidence and arguments, rather than who supplies them.
If Scott Doney’s testimony had been less normative, I wouldn’t have been tempted to look for alternative view points on this.
Actually, the 2010 NRC report on ocean acidification is probably the best overall review of the topic. My starting point was testimony from the hearing (I am interested in normative behavior by climate scientists when giving testimony); I was put off by the lack of mention of uncertainty so I sought a counter perspective. So one of my main interests in Doney’s testimony is the normative behavior. If I intended this post to be primarily about state of understanding on the topic, I would have stuck with the 2010 NRC report.
See the Annual Reviews of Marine Science article, “Ocean Acidification: The Other CO2 Problem,” with Downey as lead author (http://www.annualreviews.org/eprint/QwPqRGcRzQM5ffhPjAdT/full/10.1146/annurev.marine.010908.163834) It states:
4. Our present understanding of potential ocean acidification impacts on marine organisms stems largely from short-term laboratory and mesocosm experiments; consequently, the response of individual organisms, populations, and communities to more realistic gradual changes is largely unknown (Boyd et al. 2008).
5. The potential for marine organisms to adapt to increasing CO2 and the broader implications for ocean ecosystems are not well known; an emerging body of evidence suggests that the impact of rising CO2 on marine biota will be more varied than previously thought, with both ecological winners and losers.
6. Ocean acidification likely will affect the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean as well as the seawater chemical speciation of trace metals, trace elements, and dissolved organic matter.
Doney’s testimony did not provide this same sense of uncertainty. Nor did he mention the existence of disagreement and countervailing evidence. Given Doney’s ‘oversight’ in this regard, I would like to understand what basis for disagreement exists and what is some of the countervailing evidence, and what are the main areas of uncertainty. If the ‘mainstream’ experts don’t supply this information (i.e. evidence against as well as evidence for), then it is left for Idso et al. to fill in the blanks.
Experts presenting one-sided evidence with little mention of uncertainty in a field ‘that is in its infancy’ ends up elevating Idso’s report probably more than it deserves.