Geo-engineering out in the cold

It seems that the IPCC are not to keen on the idea of geo-engineering. This term covers a raft of proposed solutions to the problem of anthropogenic climate change, all based on the idea that as well as (and, in more extreme cases, rather than) reducing greenhouse gas emissions, we should instead start deliberately , rather than inadvertently, manipulating the climate. And despite the IPCC’s verdict (“Geo-engineering options… remain largely speculative and with the risk of unknown side effects…reliable cost estimates for these options have not been published.”), geo-engineering options are being seriously discussed in the peer-reviewed literature. Here’s a few of the ideas out there, in order of decreasing practicality (and sanity)*:


  • Carbon capture. It’s not so much the production of CO2 that is the problem so much as where it ends up – in the atmosphere. So there is some sense to the oft-aired idea that we stop it escaping in the first place by liquefying it at the source, and then storing it somewhere. In a nice twist, the most promising candidates seem to be exhausted hydrocarbon reservoirs, which are proven geological traps for fluids and gases. The geologist in me does worry about the long-term stability of these things, and the fact that we’re leaving a nice subsurface surprise for our distant ancestors should they ever decide to go prospecting in the North Sea.

  • Other carbon sequestration methods. Planting more trees, inducing phytoplankton blooms (see below), or even cultivating large vats of algae could be regarded as carbon capture schemes, but their effectiveness in the long-term is uncertain because of turnover in the biosphere. For example, whilst modelling of “afforestation” – the conversion of marginal agricultural land to forest – suggests that it can have a beneficial effect, trees release most of the CO2 they take up in their lifetime back into the atmosphere when they die and decay, so we’d have to commit to long-term changes in current land-use to have a permanent effect. Other more technologically oriented options are also being considered; this Science article (see here if you can’t get through the subscription wall) discusses binding CO2 in the form of insoluble carbonates by reacting them with crushed magnesium silicates (an accelerated version of natural weathering reactions). The author, Klaus Lackner of the Columbia Earth Institute, has even designed these nifty towers to do the job, and it seems like one of the smarter options out there.

  • Fertilising the ocean with iron. It’s long been known that there are more nutrients such as nitrate and phosphate in ocean water than are utilised by phytoplankton and other beasties – their growth is limited by the scarcity of relatively small amounts of so-called ‘micronutrients’, particularly iron. It has therefore been suggested that we could artificially trigger phytoplankton blooms by adding iron ourselves – more CO2 will be removed from the atmosphere as the phytoplankton grow and photosynthesise organic carbon, which is stored in deep ocean sediments when they die and sink to the bottom. A nice simple idea, in principle – in practice experiments which have tried this have yet to prove any permanent CO2 drawdown. And this recent Nature study of a natural bloom shows that whilst iron is important, you also need the more common nutrients to be regenerated if the bloom is going to be sustained. For a more expert opinion on this option, read David Archer’s take over at RealClimate.

  • Dumping sulphur dioxide in the upper atmosphere. Mt Pinatubo provided a natural proof of concept for this idea – its 1991 eruption threw 15-30 million tonnes of sulphur dioxide into the upper atmosphere; this reacted with water vapour to form a sulphuric acid haze which blocked sunlight and reducing the global average temperature by 0.5 C in 1992 and 1993. Notwithstanding the technical difficulties (if we use planes, won’t that actually increase the CO2 emissions we’re intending to combat?) and expense ($50 billion dollars a year, according to this article) associated with artificially sticking 10 million tonnes of S02 into the stratosphere every few years, it certainly seems a little foolish to deliberately muck around with atmospheric chemistry when our inadvertent alterations are what’s causing the trouble – especially when the side effects we know about are further buggering up the ozone layer and exacerbating the problem of acid rain.

  • Sticking a giant sun-shade in orbit. Take your pick – one giant mirror? Thousands of little ones? Superfine, reflective mesh? Either way, the idea is the same – reduce the amount of insolation reaching the surface of the planet by sticking something in the way. But the fact that we can’t even assemble a space station the size of a couple of buses on time and budget clearly demonstrates that this “solution” is way beyond our current capabilities. A far cheaper and achievable method would be to increase planetary albedo by coating the polar regions with aluminium foil.

  • Moving the Earth’s orbit. Seriously:

    … it would require the energy of five thousand, million, million hydrogen bombs to move Earth’s orbit 1.5 million km out, which would compensate for doubling CO2 in the atmosphere.


What strikes me about many of these schemes is that even if you ignore the more far-out ones, a lot of them still require the sustained mustering of the political will and resources which have so far been completely lacking in society’s response to climate change. It’s the feet-dragging over costs and the perceived threats to vested interests and lifestyle that have stymied attempts to reduce carbon emissions, not a lack of possible technological solutions or policy options. And although there is a sort of neatness in using technology to solve the problems created by our technology, the fact that those problems were unforeseen at the time should perhaps give us some pause. Still, given that the next few decades are a critical time in any efforts we make to mitigate our effect on the climate, a reasonable case can be made for using carbon sequestration (the first two options above) to buy us some more time to wean ourselves off fossil fuels, which is fairly obviously going to be a long and difficult withdrawal. The challenge is making sure that we keep that long-term goal in mind; we don’t want to give up the cigarettes, only to get addicted to the nicotine patches.
*I suspect -hope- that the IPCC is only trash-talking the Populous type options (items 3 or 4 and above), as these are the ones that get most play in the media. But as this essay points out, given the global distribution of humanity pretty much anything we do regarding climate change – from land use up – could be regarded as geo-engineering.

Categories: environment

Comments (4)

  1. Ron Schott says:

    I don’t have the reference handy, but I recall a couple of years ago some scientists proposing damming the Straits of Gibraltar as a way of regulating the salinity flux that affects the Atlantic circulation system and by extension the global conveyor belt. It was a front page article in EOS, if I recall correctly. Now that’d be large scale geo-engineering.

  2. Ron Schott says:

    Climate control requires a dam at the Strait of Gibraltar: Eos, Transactions, American Geophysical Union 78, no. 27 (19970708): 277, 280-281

  3. Chris says:

    Re: Iron in the sea.
    I went to a talk a few years ago by a guy who was involved in the Southern Ocean Iron Enrichment experiment. I think the gist of the idea is that the polar seas, esp. the Southern Ocean, are hugely productive, but limited by the availability of iron.
    They dumped many many bags of iron (can’t remember what form) off the side of a ship, and some time later there was a great swirl of chlorophyll visible by satellite (they missed the initial burst because of heavy cloud). The problem is, he said, that the suface-water circulation carries nutrients through the Southern Ocean and up to temperature and tropical waters. If you iron-fertilise the Southern Ocean, the phytoplankton there will suck up all the other available nutrients (silicon is the next most limiting, I think, and you need far more of that than you do of iron). Which means that the next sea in line won’t get any, and you’re back to square one with interest.

  4. Chris Rowan says:

    Ron – wow. Of course, it would probably be easier to get the current US administration to sign up to Kyoto than get Spain and Morocco to agree to that (or anything, for that matter)…
    Chris – that’s interesting. I think that the other problem was that they didn’t detect any “export production” – most of the excess phytoplankton seemed to be eaten and respired by zooplankton in the surface ocean, so there was no permanent CO2 drawdown.