A number of geoengineering schemes have been percolating throughout the scientific community and the media as potential solutions to climate change. Warming could be slowed by injecting sulfur into the atmosphere to reflect sunlight. Adding iron to the ocean could promote algal blooms that would help sequester carbon dioxide. Giant mirrors could reflect light away from Earth.
In an essay in this week’s Nature Geoscience, phytoplankton ecologist Philip Boyd, at the National Institute of Water and Atmospheric Research, in New Zealand, urged the scientific community to seriously evaluate these geoengineering schemes and toss out the clear losers.
IEEE Spectrum ’s Monica Heger talked to Boyd about the different geoengineering ideas, how they should be evaluated, and when, if ever, we should use them.
IEEE Spectrum: Why do you think these geoengineering schemes need to be examined now?
Philip Boyd: Well, these schemes are continuing to proliferate, and at some point the scientific community has to look at them carefully. A number of these ideas have never been tested, yet if you look in the popular literature, they receive a disproportionate amount of attention. There are very complex issues associated with geoengineering, so we really have to think carefully about it. Some ideas clearly aren’t going to work.
With the publication of the recent Stern Review on the Economics of Climate Change—a British report estimating the cost of not mitigating climate change—and also some recent modeling studies, it does seem that time is not on our side.
Therefore, it would be useful to rank these geoengineering schemes and then focus on one or two that show the most promise. And after we’ve done that, put the rest of them to bed once and for all.
Spectrum: Can you describe the criteria used to judge the different techniques and how you weigh the criteria?
PB: Well, this is a difficult issue because there are so many unknowns. What we’ve tried to do is identify the four criteria that are the most important, which are efficacy, cost, risk, and time.
So, under effectiveness, there’s the actual rationale for the idea. In some cases the schemes are just based on theory, and in other cases they have a bit more meat to them; there is actually some precedence. For example, the group that’s keen to push ahead with the injection of sulfur particles into the atmosphere, they’ve based some of their evidence on data from volcanic eruptions.
For cost, people have come up with cost estimates, and in most cases they’ve all been overoptimistically low. What we’re saying is we really have to look at the potential side effects, and those have to be built into cost.
Issues of risk also have to be factored in. With the injection of sulfur particles into the atmosphere, there are side effects like acid rain and ozone depletion. In other cases, the side effects are unknown, or we don’t really understand them.
And then the final one is the issue of time. How quickly will the scheme mitigate climate change? And if something goes wrong, how fast can we stop it? So, for example, take the injection of sulfur particles into the atmosphere. If we had to hit the emergency stop button, the particles would continue to circulate in the atmosphere and have an effect for several years. But for ocean fertilization, putting nutrients into the ocean could have an effect for decades.
These are the four main criteria. But it’s really up to society to decide their relative importance in tackling climate change. If people decide to go with the high-risk, high-efficacy scheme, that will have ramifications. Whereas if we go for something that is high cost but low risk, then it very much changes the way some of these schemes might be perceived.
Spectrum: Which schemes are the most promising and why?
PB: The one I favor the most is atmospheric carbon capture. That is the direct capture of carbon dioxide using some sort of scrubbing system. There have been proposals from U.S. researchers where they’ve described a medium-sized water-tower structure with a turbine system. As the wind blows through, there is a scrubbing device, which has a chemical absorbent that absorbs the carbon dioxide. Then the carbon dioxide can be converted into a solid and stored so that it can’t impact climate. And with these towers, it is possible that they could be incorporated with wind turbines, so you’re actually generating power to help drive the process.
The reason that one gets a vote is, although it’s one of the more expensive ideas, it is much lower risk. In terms of an emergency stop, it can be shut down quickly, and you can verify how much carbon is being removed.
Spectrum: Which, if any, should be abandoned and why?
PB: The ones that don’t have promise are anything involving biology or ecology. There are too many examples where people have done a simple introduction of a species to control another species, and it changes the whole ecosystem. There are just too many unknowns. So certainly the least promising would be the biogeochemical schemes. Those would include the ocean fertilization scheme and putting nitrogen into the coastal ocean.
Spectrum: What will be the tipping point for putting one or many of these schemes into practice?
PB: I think this is one of the reasons why we wrote this commentary, and it goes back to your first question of why do we need to look at them now. A tipping point would be if we start to see a significant number of feedbacks on climate change, and those feedbacks create a large and unexpected jump in climate change—such as the ice cap melting. Before that happens, I would argue that it’s important to rank these geoengineering schemes and have what I call a ”climate change toolbox.”
If the schemes have been tested and trialed, then if there is a tipping point, we’ll know if we have anything in our climate change toolbox. And we can either say, no, we don’t have anything in our toolbox, or we can say, well, we have this one thing, but it’s going to cost a lot of money.
Rather than seeing another 55 articles in Scientific American or Newsweek on geoengineering, it’s time to get real with it. These things are here and they aren’t going to go away, so let’s get the scientists to evaluate them so we’ll be in a place to make a good judgment call.