Suppose you believed the world was getting warmer due to humanity’s greenhouse gas emissions and you worried about it but you cant get yourself to believe that the 200-odd countries in the world are ever going to agree to drastically reduce their emissions via some joint scheme, partially because it is too hard to measure many emissions, partially because it might take a world dictatorship to actually enforce such a deal, and partially because some countries are most likely going to be much better off if the world warms up and hence are going to sabotage any joint plan. You would find yourself backed up in this opinion by a lot of auxiliary data on the difficulties of letting go of the growth fetish, ranging from the known miniscule effect that the ETS schemes currently on the table would have even if they were agreed upon, to the factoid that China is building two coal powered stations a week, to the factoid that in nearly every election politicians promise their electorate more economic growth (read: bigger cars, more holidays to far-away places, more gadgets running on energy, etc.), to the factoid that even the European countries who have been calling for reductions in emissions for over 2 decades have themselves been happily burning the midnight oil.
For people like this, which includes me, geo-engineering seems the only realistic way forward, i.e. some kind of technological fix that can be implemented by a single worried country or a sub-set of countries desperate enough to try unproven technology to cool the planet down. No world dictatorship or elusive coalition needed, hence much less of a free-rider problem. How serious are good scientists thinking about such technological fixes, what are the front runners, and are the front runners indeed things a sub-set of countries could implement?
It turns out that the possibility of geo-engineering is taken much more seriously in the academic community than youd ever think from reading the newspapers. English scientists in particular seem to have adopted the idea that they should look for technical fixes, just in case the world coalition on CO2 emission reduction doesnt quite live up to the dreams of its adherents. The Royal Society for instance advocated research in geo-engineering quite openly (see here) making it clear sensible people are thinking about this option seriously. Find over the fold a basic breakdown in basic options and their characteristics.
The geo-engineering options fall in two categories: trying to get the CO2 out of the air or reflecting more sunlight before it is absorbed (SRM: Solar Radiation Management).
On the first, the UK Institute for Mechanical Engineering put out a paper (here) where they look at several options. One of their favoured absorption plans is artificial trees, where the trapped CO2 has to be buried underground. The tough thing about this option is partially the cost of these artificial trees (reportedly 20,000 pounds per unit of which youd need 100,000 to only cover the UK transportation sector, meaning youd be talking about hundreds to thousands of billions of dollars for the world as a whole) but also the problem of how to actually store the huge volume of CO2 (abandoned oil fields are touted, but this is not as easy as it sounds). Nevertheless, it can be done by a subgroup of countries if it has to be done, though we might end up digging an awful lot of big bunkers deep into the ground to get rid of all this CO2.
Another favoured solution by these mechanics is to capture CO2 in algae, either directly in coal-fired plants or as algae strips on the sides of buildings. The obvious problem is again that one would have to bury an awful lot of algae somewhere, but in principle it is a solution that can be implemented unilaterally at great cost. The suggestion to use the algae as fodder for animals is probably more cost-effective but has the obvious disadvantage that this doesnt get the CO2 out of the whole system.
The last of the favoured absorption solutions is to try to get the oceans to absorb more CO2 via all manners of Ocean fertilisation, with the saturated algae drifting to the bottom of the ocean with all their CO2 trapped in them for a long time. So far this option has proven harder than hoped, with the well-known failed attempt to get sustained massive algae blooms via pouring some iron into the water. Apparently, some Australian scientists are involved in seeing whether nitrogen and phosphates would be a better idea to put into the water than iron, but the technology looks quite dicey at present. In particular, unlike the other ones so far talked about, there is much more risk of doing unintentional harm by adding massive amounts of chemical substances into the ocean as opposed to burying some CO2 captured in one way or another.
If we then look at the SRM solutions, a couple of interesting ones have popped up in the UK reports. One of the mentioned solutions by the Mechanics is to paint all the buildings white so that they reflect more sunlight. This is clearly the kind of thing that might well capture the public imagination (save the planet: paint your roof white), but it is much harder and expensive than it sounds. For one, I understand wed have to reflect something like the whole area of Australia back into space to reduce the temperature, which is far more than merely the surface of all the buildings in the world. Also, white roofs tend to get dirty over time and the paint may not itself be all that environmentally friendly either. Hence, were talking a high cost, high maintenance solution that might well be more useful as a symbolic DIY policy rather than as a serious option. Yet, the potential downsides of this method seem smallish in the sense that no-one sensible is going to insist on the impossible pre-requisite of knowing with certainty that we wont be doing unintentional harm by reflecting some more sunlight via white buildings.
The Royal Society also reviewed a whole set of possible SRMs (see here). One of their most recommended options is to put sulphate aerosols in the stratosphere above natural levels, causing an increase in planetary albedo and thereby reducing the incoming solar radiation. The obvious problem with putting massive amounts of a chemical (SO4 and the like) into a particular region of our air is that there is the potential danger of unintended consequences. Yet, it is the kind of thing with which an individual country can experiment and something of which the consequences can be learned about by trial and error before implementing it on a massive scale.
A more outlandish option is to put reflectors in space so that less sunlight hits the earth. An L1 point shield would be best placed at a particular point between the earth and the sun so that it is kept there by the combined gravitational pull of both bodies. An interesting sideline of this whole area (which has really generated the enthusiasm of a whole horde of engineers who have each come up with their own variant) is that they have figured out you only need to deflect sunlight by a tiny amount such that it misses the earth. My problem with this option is that it would seem fantastically expensive to put enough mirrors into space to reflect the equivalent of the total radiation hitting Australia without anything going wrong. These mirrors have to be in exactly the right spot, themselves deflected easily by the smallest of gravitational pulls from comets or what-have-you (and if you’re deflecting the equivalent of the total amount of sun-energy hitting Australia, you can imagine the destructive force hitting those mirrors if they are not in exactly the right angle). It basically does not sound plausible at this point that we will be able to do this now or in the coming century or so.
Another interesting idea is to get the clouds to be whiter in order to reflect more sunlight. The way to get whiter clouds appears to be to generate better mini water droplets and a whole host of options exist to attempt to do this, including ocean sprays and particular forms of coal dust that form the nucleus of these droplets. The potential disadvantages of trying it appear smallish of this option (whatever we put into the air will be quickly going back in the form of rain so it is hard to imagine permanent damage from putting something into the air of which there is already quite substantial amounts in the air), but whether it might work or not appears completely unknown.
Summarising, there are respectable scientists spending their time on geo-engineering solutions, with the above merely being the front-runners of dozens of proposed schemes. None of the proposed solutions talked about above appear to be thought of as proven and implementable at acceptable costs with minimal risks at this point, but as someone who basically views the whole global ETS carnaval with bemused incredulity I am heartened to see serious thought is put into what we might actually end up doing as a subset of desperate countries and that there appears to be some hopeful candidates on the table.
Of course, having said all this, my front-runner for what will actually happen is that the world as a whole will simply adapt to whatever climate change our energy-guzzling way of life condemns us to. Should geo-engineering really be implemented by a subset of desperate countries then the problem will be that the optimal climate for one country may not be the optimal one for another, i.e. those countries currently secretly happy with climate change may well move in the opposite direction with their own geo-engineering if the promised warming of the planet is thwarted by someone else. We may thus end up with climate wars where, say, Russia does its best to pump as much CO2 into the air as it can and Canada paints all its buildings black whilst, say, Australia puts SO4 into the stratosphere and Japan fills the oceans around it with phosphate. Perhaps such climate wars in turn will lead to a geo-engineering dis-armament UN body. You can just imagine the UN inspectors checking that the buildings in Vancouver are not all black! All such humour aside, the possible political dynamics of geo-engineering are scary.