I've just finished reading Hack the Planet, and I highly recommend it to anyone with an opinion on climate change (which really should be everyone). Eli Kintisch has written a comprehensive guide to the debates around geo-engineering, but it's also a strong argument for reducing our CO2 emissions. Like me, he's an unabashed believer in the scientific method as the best process for answering questions of fact and he's not afraid to challenge his subject's assertions. It's fundamentally a documentary approach, not a polemic, but all the more powerful for how he tells the stories of those involved in the debate.
The core of the book is the idea that we may need to perform engineering on a massive scale to mitigate the climate changes caused by increases in greenhouse gases. There's a wide variety of schemes, from seeding the upper atmosphere with sulphur to reduce incoming radiation, spraying salt water into clouds to increase the amount of light reflected, scrubbing CO2 directly from the atmosphere or sequestering it underground as we're generating it. His conclusion is that the potentially cheap options, like injecting new material into the atmosphere, are risky and unproven, while the safer ones, like capturing CO2 as it's generated, are way too expensive to be practical.
The risks mostly come from our extremely poor understanding of how the planet actually works. We've had a few natural experiments with volcanic gases emitted by eruptions which demonstrate that cooling does occur, but also that rainfall and other patterns may be radically altered. Research may help quantify the risks, but the large-scale field trials needed face widespread public opposition. That also highlights a long-term political risk; if war or other disruption stops the engineering effort then the climate could change suddenly and catastrophically. On the other hand, it's also vital that we understand as much as possible about the techniques. If we end up with a 'long tail' event causing far more severe climate change than we expect, we may need to rapidly implement something as an emergency measure.
That all makes me hope that we can bring the costs down of sequestration technologies. The outlook there is uncertain, despite a lot of smart folks attacking the problem the costs of capturing one ton of carbon are still far too high to be deployed commercially. I'm optimistic this will change, but it's sobering to see the history of high hopes and broken promises from the proponents.
After his detailed view of the realities of the different geo-engineering approaches, reducing emissions emerges as a far more attractive option. As an engineer I'm inherently drawn to technological solutions, and if I was an investor I'd be betting on some form of carbon capture working out in the end, but in software terms this book paints the planet as the most convuluted legacy system you could imagine. We'll never be quite sure what will happen when we monkey with its spaghetti code, so lets hope we don't have to.