Have you ever gone camping with someone who doesn’t know how to build a fire? It might go something like this: you get a pile of twigs burning, and immediately your friend starts piling on huge logs. The fire dwindles. “Hey,” your friend says, “This fire sucks. It must need more logs.” If some fuel is good, then more must be better. It’s a terrible way to roast marshmallows. And yet it’s the philosophy that Dr. Everett applies to the effects of increased carbon dioxide on life.
Here’s an example from part I of his testimony:
“We should also consider that CO2 is required for all plant life and it is in short supply, to the point it limits growth rates for most plants. This is yet another clue regarding impacts.”
The problem is that in general, this isn’t true. In the oceans, where much of the world’s photosynthesis takes place, iron is relatively insoluble: it’s the limiting nutrient (PDF). This is especially true in the tropics, where the surface stays warm, preventing convection from bringing nutrient-rich water up from below. That’s why tropical oceans are so clear and blue: there’s nothing growing in them. And as global temperatures increase (the Other-other CO2 problem), this desertification is likely to spread from the tropics.
On land, plant growth is limited by soil nutrients: phosphorus, potassium, and nitrogen are the big three. And though increased carbon dioxide may spur growth in some plants, it’s unlikely to be sufficient to offset human emissions, and may come with other undesirable effects, such as changes in the nutritional content of crop plants.
We saw in part II.5 that Dr. Everett bases his carbon dioxide projection on a single, unrepresentative slice of a much larger dataset. He does the same thing with the scientific literature in part III, which is devoted primarily to dismissing concerns over the effects of acidification on organisms which build their shells out of calcium carbonate:
“A good example is the dispute over whether acidification is good or bad for “shell”-forming plant plankton, a vital part of the ocean’s biology with the ability to sequester vast amounts of CO2. The first paper says more CO2 is good, the second that it is bad, and then the first successfully refutes the criticism and gets the last word, sustaining the positive assessment in great detail – all published in Science. This is important because much of the alarmist literature is based on work that is refuted in this series. The verdict: shell forming algae do much better in a higher CO2 environment.”
The “first paper” in question is “Phytoplankton Calcification in a High-CO2 World” by Dr. Iglesias-Rodriguez and colleagues. (PDF) What they found was that certain coccolithophores (calcifying phytoplankton) build thicker shells in response to increased carbon dioxide (later, we’ll see that this doesn’t mean that acidification is “good” for them- or anyone else).
This is interesting, but by itself it doesn’t necessarily tell us much: it’s only one study, looking at a single species of a single calcifying organism. To talk about the effects of acidification on calcifiers, we need to look at all of the information that we have. Here’s a chart summarising the effects of increased carbon dioxide on various organisms:
Coccolithophores, like those studied by Dr. Iglesias-Rodriguez and colleagues, have a variety of responses to increased carbon dioxide. However, the available data, as a whole, tell us what we already suspected: acidification negatively impacts calcifiers.
Other parts of this section are even more misleading. For example, referencing a chapter of the IPCC-AR4, Dr Everett says:
“Also, the latest IPCC report (summary above) found no empirical evidence supporting effects of acidification on marine biological systems”
What the IPCC report actually says is:
“However, the effects of recent ocean acidification on the marine biosphere are as yet undocumented. […]Although laboratory experiments have demonstrated a link between aragonite saturation state and coral growth (Langdon et al., 2000; Ohde and Hossain, 2004), there are currently no data relating altered coral growth in situ to increasing acidity.”
In other words, there is empirical evidence for the effects of acidification on corals, in the form of controlled laboratory experiments. It’s not that data from the wild disconfirm the predicted effects, it’s that data from the wild didn’t exist yet. On the other hand, this report lists changes in acidity (albeit natural ones) as a confounding factor in studying the effects of climate change on coral reefs, so we can at least agree that it acknowledges the dependence of coral communities on pH:
“In addition, inter-decadal variation in pH […and other factors…] make it more complicated to discern the effect of anthropogenic climate change from natural modes of variability”.
One such effect of climate change is coral bleaching, which is discussed in the IPCC-AR4:
“There is now extensive evidence of a link between coral bleaching – a whitening of corals as a result of the expulsion of symbiotic zooxanthellae (see Chapter 6, Box 6.1) – and sea surface temperature anomalies (McWilliams et al., 2005).”
Dr. Everett doesn’t mention coral bleaching, let alone this study (published after the AR4, but before his testimony) suggesting that stress from acidification combines with thermal stress to make bleaching more severe.
In fact, he ignores or misrepresents so much in this part of his testimony that two of the authors he cites have responded to clarify that their studies don’t support Dr. Everett’s position. We’ll look at what Dr. Ries and Dr. Iglesias-Rodriguez have to say about his testimony next time.
Anthony, K., Kline, D., Diaz-Pulido, G., Dove, S., & Hoegh-Guldberg, O. (2008). Ocean acidification causes bleaching and productivity loss in coral reef builders Proceedings of the National Academy of Sciences, 105 (45), 17442-17446 DOI: 10.1073/pnas.0804478105