There’s recently been another ripple of media attention to the other CO2 problem: Not climate change, but ocean acidification. In brief: The oceans absorb a portion of CO2 emissions; this mitigates greenhouse warming, but forms carbonic acid, lowering ocean pH. Acidification of the oceans impedes the formation of coral and shells, and within decades, if trends continue, the calcium carbonate that forms the skeletons of many ocean organisms will become unstable and simply dissolve. Scientists expect that, well before that point, most coral reefs and the ecosystems they will be deeply disrupted or destroyed.
The fact that this problem exists is slowly percolating into the public mind. Understanding of a crucial aspect of the basic cause-and-effect relationship, though, has gotten approximately nowhere. This understanding is derailed by an insidious comprehension-gap, an amplified form of a comprehension-gap that derails understanding of a crucial aspect of the climate change problem.
Reducing the Rate of the Rate
In “Greenhouse Gases and Advanced Nanotechnology”, I described a problem at the climate-change level: Almost everyone mistakenly thinks about cause-and-effect as if CO2 were the more familiar kind of pollutant, with a pollution level is proportional to the emission rate. Instead, it is like water flowing into a bathtub with a nearly-blocked drain: Unless the flow is reduced to a trickle, the water keeps rising and the tub overflows. Short of very deep cuts, reducing emissions reduces not the CO2 concentration, but the rate of increase of the CO2 concentration. (To quote an estimated 5,000,000 web pages, “Read the FAQ”.) Likewise, capping emissions wouldn’t cap the concentration; it would cap the rate of increase of the concentration.
This is a reality that seems unlikely to make its way into widespread understanding. The comprehension gap is too large.
Now, one more level: An increment in CO2 concentration takes years to have its full effect on the acidity of surface water in the oceans, hence, on short time scale, capping CO2 emissions wouldn’t cap acidification, it would merely cap the rate of increase of the rate of increase of acidity. [9 June 09 amendment: The “short time scale” here is a bit too short. Mixing of deep and surface water is fast enough that the lag is small on the relevant time scale: For practical purposes, surface-water pH tracks CO2 concentration.]
Ocean temperatures also follow a model one integration level deeper (capping emissions = capping the rate of increase of the rate of increase of the ocean temperature), and do so more accurately, not just on short time scales. Ocean warming and cooling are slow processes of great importance to climate. A paper published this week in the Proceedings of the National Academy of Sciences (US) states that
Following [a hypothetical] cessation of emissions, removal of atmospheric carbon dioxide decreases radiative forcing, but is largely compensated by slower loss of heat to the ocean, so that atmospheric temperatures do not drop significantly for at least 1,000 years.
The paper is titled “Irreversible climate change due to carbon dioxide emissions”.
It would be advantageous to reduce the atmospheric CO2 concentration relatively quickly. This can be accomplished only be removing it, not by capping, reducing, or eliminating emissions (nor by putting it in the sea!).
This objective could be accomplished by generating about 1021 J of electrical energy and applying it, with reasonable thermodynamic efficiency, to concentrating and removing the industrial-era anthropogenic excess CO2 from the atmosphere. This amount of energy is equivalent to about 3 TW for 10 years; current global electric power production is somewhat over 2 TW. A project like this seems unlikely to be practical until we have climbed the ladder of technologies that leads to molecular manufacturing.
Update, 9 June 09: