A Speculative Political Ecology of Genetically-Modified Carbon-Capturing Trees
I'll say up front that of the geoengineering proposals out there, some form of carbon capture and storage is the most reasonable, and I think worth pursuing in some form. (It's far better than the other most popular idea, shooting massive amounts of sulfur into the upper atmosphere to shade the Earth -- I can't imagine such a plan not having catastrophic unintended consequences.) Nevertheless, I think Dyson's plan for carbon-capturing trees (CCT) is a bad way to approach the problem.
Most of the ridicule has centered on Dyson's optimistic estimates of how quickly the technical barriers could be overcome (in terms of timeliness, and of making the carbon capture effective). I'm willing to grant him that, because what's more interesting to me is to try to imagine how the political ecology of implementing the technology would play out. We have enough experience -- from reforestation schemes in India, ecological reserves in Brazil, palm oil plantations in Indonesia, old-growth logging in the USA, etc. -- to make some reasonable predictions on this front.
The first thing that would have to be done is to make CCT worth people's while to plant. The obvious mechanism here would be a carbon tax -- either the government would collect the tax from carbon emitters and pay it own agencies, or a private firm, to carry out the planting, or carbon emitters would preemptively plant CCT to offset their emissions and reduce their tax burden (or ensure compliance with a more command-and-control type of carbon regulation). It's likely that mainstream environmental NGOs would get in on the action, planting CCT as part of their mission to improve the environment. The main point here is that it's big, elite-controlled institutions that are going to be able to access these funds, to sell their proposals to the money-controlling agencies (though it's possible that poor households will be used as the footsoldiers, on the pattern of many resettlement and cash-crop-encouragement schemes in the Third World).
So if we have CCT seeds, and money to make planting them profitable, the last thing we need is a place to plant them. The search for this land is likely to result in significant social injustice. It would be simple if we could just replant the extensive areas of the Earth that have been deforested over the past couple centuries. But forests are not simply cut down and abandoned -- that land gets used for other things (farms, homes, etc.), and the people living there may, rightly or wrongly, not be keen on having their land reforested. Dyson, to his (inadvertant?) credit, does recognize that most CCT will be planted on land that is currently forested with non-CCT.
In either case, however, we have to ask how the CCT planters will get access to the land. I'm going to go out on a limb here and predict that CCT will get most of its land the same way as virtually every other big-money land use project ever -- it will be stolen (morally if not legally) from vulnerable populations, especially indigenous people. Governments, of whatever level of ostensible democractic-ness, (and some land-owning corporations) will hand out permits to plant CCT in certain areas, disregarding the existing local uses of the forests. Around the world, poor and indigenous people have repeatedly been -- and are still being -- forced out of land they had used for subsistence activities because the authorities wanted to use it for logging, industrial plantations, or wilderness-style nature reserves. This would lead to severe negative impacts on the displaced people, as well as potential militarization of the area to prevent sabotage by disgruntled peasants (and simply attempts to continue using the land).
Dyson imagines that, with CCT in place, the forest ecology would bounce back and the forests would be able to serve a dual role -- carbon capture and the other ecological benefits we get from preserving natural forests. I think there are three reasons to be skeptical of this. First, we have to consider the incentives in place. The dominant incentive is going to be to "produce" carbon capture. The money is coming from taxes (and perhaps charitable donations) aimed at removing CO2 from the atmosphere. So the clearest and easiest way to measure payouts is to pay per CCT or per unit of CCT biomass. In the face of such a bureaucracy-friendly indicator, side constraints demanding ecological preservation are likely to be weak in practice. The result will be carbon farms, not functioning naturalistic ecologies. This problem would only be exacerbated if, instead of simply sequestering the carbon, the trees produced something marketable -- such as fuel -- from it. That would add a second motive running counter to preserving the prior ecological values of the forest.
Second is that the CCT would not be suitable for preserving the pre-CCT ecology. Current forests contain a great deal of biodiversity, both intra-species and inter-species. CCT, however, will have a much more restricted range, being one variety each of a few species (particularly if, in the interests of defending their intellectual property, the genetic engineers insert some equivalent of the terminator gene or make the carbon capture gene recessive, thus preventing the CCT from incorporating the existing diversity in their wild relatives). Even-aged dominant-species monocultures are unlikely to be optimal for preserving ecological balance, even assuming (probably over-optimistically) that the projects always use genetically modified versions of species native to the biome where they're being planted.
Finally, bouncing back is a time- and space-intensive process. It takes time for trees to grow. And for the ecosystem to recover from a disturbance of the replanting-new-trees type would require a substantial area of undisturbed area in the neighborhood from which other species could spread back in. The likelihood that the genetic modifications would be preferentially made to fast-growing "weedy" species like pine, in order to let CCT operations get up and running quickly, would partially address this point at the expense of exacerbating the previous one.
Ultimately, these ecological problems with CCT plantations will not just hurt the environment (and thus indirectly all of us), but they will specifically hurt the people living in those ecosystems. I can imagine a potential limited role for CCT, in cases where people are intending to replant trees anyway (e.g. for shelterbelts between farms). But there would have to be safeguards in place to prevent the emergence -- and environmentalist endorsement -- of large-scale CCT plantations. Meanwhile, mechanical-chemical routes to carbon capture seem more promising as a way of undoing the effects of our emissions.
(The speculations in this post are based on a wide variety of political ecology studies I've read. The most on-point one is Paul Robbins' "Tracking invasive land covers in India" from the Annals of the Association of American Geographers in 2001.)