Photo Credit: NASA
I posed this question in a posting way back in December 2007. It appears to remain largely unanswered (or possibly ignored?); but, in the light of the recent announcement by our government regarding proposals for a new generation of coal-fuelled power stations, I feel it could stand another airing. The unease I feel is this: quite apart from the whole raft of concerns raised by others in various places, there is the fact that for every 12 tonnes of carbon burned in fossil (or any other carboniferous ) fuel, approximately 32 tonnes of oxygen is extracted from the atmosphere. The scale of this "oxygen depletion" may, admittedly, be exaggerated somewhat because many fuels actually have a bound-in oxygen content to begin with, but still it is probably a good order-of-magnitude figure.
Now if the fuel is from a renewable source, then I suppose we can generally assume that the usual biological processes such as photosynthesis will eventually return the consumed oxygen to the atmosphere and, on balance, there is no adverse effect; if the fuel was from a fossil source, then although there will be an excess carbon dioxide input to the atmosphere, it is still conceivable that a proportion of it will also be "metabolised" by the ecosystem: for example, there may be accelerated/enhanced growth of vegetation, algae, etc in some land/sea areas, which could partially off-set it ...for a while.
Some of the excess carbon dioxide will surely not be recycled, though, and it is that fraction that we get concerned about with regard to global warming, of course. But as well as this hazard, there is the associated potential problem that a portion of the oxygen removed from the atmosphere by combustion is lost permanently. That would be bad enough in any case, but if all the carbon dioxide from a power-station were to be sequestered below ground then all of the oxygen consumed in its combustion process would go with it - for good; or at least for "... five thousand years at least ..." (which of course begs its own questions as regards the really long-term future of the planet).
So on this basis, it seems to me that what we should be aiming at, if anything, is true carbon-capture, and not capture of carbon dioxide. We should in other words be separating out the oxygen first and returning it to the environment.
And here we encounter a further little niggling problem: splitting carbon dioxide into its elemental components takes ... yes, you guessed it - energy! Logically (one assumes) this should not come from the burning of yet more coal, but maybe it could be provided by truly renewable sources such as wind, solar etc, or - if we really must - nuclear fuel.
So, why not just invest in them properly in the first place?
To be fair, there is now apparently an experimental plant in Germany that "cooks" sewage anaerobically to drive off the volatiles, which then become "new" fuel without comsuming oxygen. The only true waste is basically carbon black (charcoal) which actually has a commercial value in its own right, but does not present a global-warming risk. Of course, this approach is a rather different proposition from the coal-fired argument discussed above.
Now don't get me wrong - I am a firm believer that we face a lethal threat from human-generated global warming, and that all proposed solutions need to be examined properly and fairly. But that means identifying potential drawbacks too.
Perhaps I am being overly naive in my arguments relating to oxygen depletion, and maybe the effect will never be great enough to cause us concern. I just don't know. But I'd be really glad to hear other views. What do you think?
[Of course there are plenty of other arguments against this carbon-capture approach. For one thing, it doesn't avoid continued plundering of the earth's resources; and the supposed (by some) unsightliness of wind-turbines is surely as nought compared to the huge and visciously ugly scars left behind by open-cast mining operations? Then there is the matter of security of the energy supply. We would continue to be at the mercy of off-shore providers. Or am I very much mistaken?]
Mike
