Monday, June 20, 2011

Models cannot trump reality

kw: debunking, climate change, disasters

A project named EPOCA, for European Project on OCean Acidification, aims to determine just how much trouble shellfish will be in with increased CO2 levels, in the range up to 1000 ppm. There are two parts to this question:
  1. How much harder will it be for shelled marine creatures to produce calcite and/or aragonite shells?
  2. How rapidly, if at all, will those shells dissolve back into ocean water, at various levels of atmospheric CO2?
It is to be hoped that useful answers to the first question can be answered with the experiments currently being carried out off the shore of Spitzbergen (By the way, I wonder why they aren't also trying it in more tropical waters, which dissolve much less CO2?). The answer to the second question is already known, and it is, "Not at all, or very slowly." Why do I say this?

The blue line on this chart is of interest here. It represents CO2 levels, measured by various proxy and semi-direct methods, for the past 450 million years. Note the tiny horizontal segment at lower left. That represents the past several million years, the period since the evolution of C4 photosynthesis, since which time CO2 levels have been lower than at any period in prior history!

I spent many years happily collecting fossil shells from deposits throughout the geologic series from Cambrian times right through the mid-Pleistocene (550 to 2 million years ago). Let's consider the Triassic, a period during which the CO2 level was four to five times what it is today. I have a lovely Triassic ammonite shell, with mother-of-pearl colors still evident. I don't know how long it was exposed to carbon-rich ocean waters after the death of the host animal, but it survived unscathed, even un-etched, for all the time since, some 200 million years.

Environmentalists fear that "modern" species will have "forgotten" how to make calcite or aragonite shells from more acidic waters, in the past few million years. The energetics of shell production may have changed, so that they are easier to produce now, but it is not likely that there is a difference in kind between ancient shell-producing chemistry and the modern version, just in intensity. A generation is pretty quick among shellfish. While the oceans may be acidifying at a rapid clip, compared to geologic rates, it is still rather slow compared to the adaption time frame of animals that have one or more generations per year, and plankton that have several generations per month. There is another factor to consider.

Suppose it takes several percent of a creature's energy budget to produce its shell. Further, suppose at some level of ocean acidification that requirement doubles. We must remember that it does so for all shellfish. No species or genus is going to have some kind of broad selective advantage over others. They will all be affected equally. In any species, some individuals will have a little more efficient shell-producing organs than their conspecifics, and this will continue, year after year, generation after generation. Genetic drift is more than sufficient for the species to keep up and continue making shells. I expect the EPOCA experiments to show that all species considered will have widespread ability to cope with acidification at all carbonation levels.

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