With the new Summary for Policymakers of the effects of global warming out (as pointed to by Brian) it seems clear that if we are to avoid the worst effects of global warming, we will, globally, need to make massive cuts in emissions, and even then we’ll still cop plenty of unpleasant side effects.
However, there is an unspoken assumption here that, in large part, any CO2 we release into the atmosphere is stuck there until natural processes take it back out again. Discussion of conservation, renewables, nuclear power, and sequestration is all about putting less greenhouse gas into the atmosphere. Of the mitigation processes, only revegetation actually takes carbon dioxide out of the atmosphere and sequesters it, at least temporarily, but the capacity of this method is dwarfed by the amounts being added.
Even engineers doodling in their notepads have largely avoided the idea of artificially removing CO2 from the air. Grandiose engineering schemes to counteract global warming have largely been about reducing the amount of solar radiation that reaches the Earth, for instance by dumping materials in the upper atmosphere, or sunshields in outer space. Aside from the costs, such solutions involve a very considerable punt that they will work as predicted, with no nasty side effects.
While the big-G green attitude of simply ruling out carbon capture and storage is in my view erroneous, it is important to note that the much easier task of capturing carbon direct from fossil fuel plants is not yet been demonstrated on the scale of a commercial power plant yet. And, unlike in the power plant, the carbon dioxide in the air is incredibly diffuse. Consider a cube full of air, one kilometer high, wide, and deep. Such a cube (assuming the air was all at sea level pressure, an overestimate) would contain 1290 tonnes of air. Of that 1290 tonnes, only roughly 500 kilograms will be carbon dioxide – roughly as much CO2 as you produce by taking a plane flight from Brisbane to Melbourne.
But then again, there is one perfectly well-known and proven system from extracting bulk CO2 from the atmosphere. It’s been operating for millions of years, in fact. So if plants can do this as a byproduct of living, surely it’s not impossible to for humans to do the same, if perhaps more inelegantly?
Richard Branson and Al Gore want to know, and they’re prepared to throw 25 million dollars at anybody who can demonstrate a commercially-viable technology for doing so – though, frankly, if anybody does demonstrate a cheap-enough way of doing this, the $25 million from Branson will be chickenfeed compared to the intellectual property royalties.
In that context, Joshua Stolaroff’s PhD thesis (from Carnegie Mellon, one of the better engineering schools in the USA) makes fascinating reading. He, and his supervisor David Keith, have published several peer-reviewed papers on this material, but the thesis is free to download, so I’m linking to it.
He examines the cost of extracting CO2 from the air by spraying droplets of concentrated caustic soda through air flowing through a tower, not unlike a power plant cooling tower. From there, the captured carbon dioxide is then extracted from its chemical bind, leaving concentrated CO2 which can be disposed of in the same ways as is proposed for coal-fired power plants. His bottom line? He estimates a cost somewhere between $80 and $250 US dollars per tonne of CO2 disposed of, and identifies some improvements which would reduce that upper bound to $130 per tonne.
The first thing to note that this scheme is highly unlikely ever to be cheaper than capturing CO2 directly from fossil fuel power plants. While Stolaroff’s proposed towers have the advantage that they can be located whereever it’s convenient to dispose of the CO2, the overwhelming majority of the cost is in the capture and conversion of the CO2, rather than the final disposal. However, even at the upper-bound price of $250 per tonne, it might be practical for some purposes. Consider that Melbourne-Brisbane flight. A fully flexible economy airfare to Brisbane costs roughly $600; adding another $300 is a considerable cost, but (assuming the benefits of economic growth are fairly distributed….) by 2025 or so our real incomes should have increased to the point where, even assuming that plane flights haven’t declined in cost in real terms, a $900 flight would represent the same impost as a $600 flight now.
But there are other implications. Several authors referenced in the thesis discussion point out that air capture represents insurance, against the most catastrophic climate scenarios (well, nearly the most catastrophic – it’s possible to imagine scenarios where the change is so sudden that it overwhelms our economies and thus the ability to cope). But this represents a risk in itself; if there is a fallback technology that can save us from disaster, it represents an additional argument to delay action on climate change. This does not seem to have happened yet here in Australia, but it can’t be far away as a carbon pricing scheme comes into view and the opponents of action get increasingly desperate.
On the more positive side, air capture, particularly at more reasonable prices, might give us a chance to meet essentially any emissions reduction target at a bearable cost, and without radical changes to our lifestyles. Furthermore, it might mean that returning carbon dioxide to pre-industrial concentrations is be the work of decades rather than centuries.
I’m not sure that Stolaroff’s particular CO2-capturing scheme will work out. Neither is he. That doesn’t really matter; there are other alternatives (notably, combining biofuels and sequestration) that might be better. But, regardless, this kind of research makes me even more confident that the technologies we need to reduce our CO2 emissions as much as necessary, and without radically changing our lifestyle (or our political philosophies) are out there. All we need to do is decide, as a species, that CO2 reductions are to be made and how the burden of cost is to be shared.