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Protecting the planet

Ben Hargreaves

Practical solutions
Practical solutions

Do geo-engineering schemes have the potential to halt climate change?

A year and a half on from authoritative reports by the IMechE and Royal Society on geo-engineering, experts on this controversial and unproven science – which could have the potential to reverse the effects of climate change – believe that not enough is being done to develop it.

Professor John Shepherd, of the University of Southampton’s National Oceanography Centre and a Fellow of the Royal Society, believes that £100 million should be devoted to researching geo-engineering schemes over 10 years– instead of the £3 million of Engineering and Physical Sciences Research Council money given to it at present. “That’s 3% of what we’ve suggested – and I think we ought to have the other 97%,” says Shepherd.

Tim Fox, head of energy and climate change at the IMechE, concurs. “We need to focus very quickly on the practical geo-engineering solutions – ones where there is a consensus that they offer real possibilities,” he says.

Geo-engineering schemes are potential ways of modifying the earth’s climate through technology. The proposed ideas fall into two groups: schemes that would sequester CO2 from the atmosphere, and techniques for managing solar radiation to deflect sunlight. Geo-engineering may well represent the last chance in the climate change saloon and has many detractors, but others believe it would be foolish not to consider using it when emissions of greenhouse gases continue to rise and runaway global warming is a real possibility. 

The solar radiation management (SRM) techniques proposed include spraying sulphur into the stratosphere. It is thought that this could mimic the effects of volcanic eruptions, such as that of Mount Pinatubo in the Philippines in 1991, which released large quantities of aerosols into the atmosphere with the effect of temporarily cooling the planet. British engineer Stephen Salter, meanwhile, has done a lot of work on a scheme that could increase the albedo of clouds – the extent to which they reflect sunlight – by seeding them with seawater droplets. In the US, Professor Roger Angel of the University of Arizona has even proposed launching trillions of mirrors into space to form a sunshade, blocking out 2% of the sun’s rays.

Direct CO2 removal from the atmosphere is the geo-engineering scheme favoured by Fox at the IMechE. US physicist Klaus Lackner has proposed capturing CO2 through the deployment of hundreds of thousands of mechanical trees built with materials that absorb greenhouse gases.

Fox says: “Artificial trees offer the best potential geo-engineering activity, and really we should consider them as a form of CO2 mitigation. It’s one step beyond carbon capture and storage being used at a power plant.” The IMechE considers geo-engineering to be a crucial part of a three pronged attack on climate change which also includes mitigation of emissions and adaptation.

Some in the media have suggested that development of geo-engineering could be part of a conspiracy to enable fossil fuels to continue to be burned with impunity, but Fox insists that engineers looking at geo-engineering have no desire to see it replace efforts directed at mitigation.

Would it work?

He says: “There have been stories in the press where a conspiracy theory has been raised around the notion that there is a coming together of energy companies to try and promote geo-engineering as a solution that would allow the economy to move forward on a fossil-fuel basis.

“That is absolutely incorrect. The IMechE has been involved in the geo-engineering debate for two years and there is no such consortium. We’re independent organisations who see air capture as a technical approach to enhance mitigation.”

Many believe that carbon sequestration alone will not be enough. Brian Launder, professor of mechanical engineering at the University of Manchester, argues that, if climate change becomes an emergency, air capture schemes will not work quickly enough and so some form of radiation management will be necessary. “In a climate emergency the only schemes that can possibly act quickly enough are SRM ones,” he says. “That is why I want to see those schemes developed too. We could be faced with a situation where we want to use stratospheric aerosols and the cloud brightening scheme, or some other technique.”

Launder views Salter’s scheme for brightening clouds as one of the more environmentally benign techniques, but there are some doubts as to how it would work in practice. Shepherd describes it as “a very nice idea”. Shepherd says: “It employs natural materials. The disadvantage is that, first, we don’t really know whether you can enhance clouds by spraying seawater.

“Second, it’s not straightforward to create the spray or persuade the droplets to become cloud condensation nuclei. Until some field trials have been done, we won’t know whether this concept is right.” It’s another area, then, that could benefit from more resources being devoted to it. 

Meanwhile John Gorman, an engineer and IMechE member, has been researching some alternatives to spraying sulphur into the atmosphere. He emphasises that geo-engineering should be viewed as a practical approach to climate change. He says: “Anyone who believes, post-Copenhagen, that we will get a peak in global emissions by 2020 is living in cloud cuckoo land. Maybe we’ll be able to get them close to zero by the end of the century. Around about 2060, if we really work at it, we could get the level of greenhouses gases in the atmosphere down to about 280ppm. In the meantime, in that scenario, the temperature will have gone way out of control, so we’ve got to do solar radiation management.”

Gorman believes that spraying sulphur into the atmosphere could prove detrimental to the ozone layer, so he has been working on an alternative whereby tetra ethyl silicate would be burnt in kerosene – aviation fuel – to produce tiny particles of silicon dioxide. He believes such particles could possibly be more effective in reflecting sunlight than sulphur-based products, but needs money for his research to be tested. “With my suggestion, silica, the chances are you would be able to control fairly exactly the size of the particle by the concentration of the material in aircraft fuel. But this has yet to be researched,” he says.

Gorman’s thinking runs that spraying sulphur could enhance the mechanism whereby CFCs destroy the ozone layer because the size of the droplets is difficult to control. The larger the particle, the easier it is for CFCs to settle on it. “The reaction we don’t want to happen works better because of the stratospheric aerosols. The silicate alternative could make it possible to control the size of the particle exactly,” he says.

“The wavelength of light that is dispersed by particles depends on their size, not the colour of the surface. The central point is that you should be able to create particles of the size you want and therefore need fewer of them – which would mean less of an effect on the ozone layer.”

IMechE's choice

Shepherd of the Royal Society says: “Stratospheric aerosols should not necessarily contain sulphates. It’s quite possible that somebody will come up with a better form of aerosol.” 

Shepherd agrees with Fox that carbon sequestration from the atmosphere is the geo-engineering technique of choice but argues that it would be “prudent” to research SRM too. “The CO2 reduction methods are the preferable ones but they do take a long time to operate, so I think it would be prudent to research both varieties of geo-engineering,” says Shepherd. “Around 2050 we might find the temperature rise has exceeded two degrees and people agreeing that we need to halt it. If we wanted to do anything quickly it would have to involve an SRM technique.”

Fox says spraying stratospheric aerosols should be researched as an option to be used in an emergency. He says: “The only area of SRM that is still worth pursuing, but as an emergency deployment device, is the injection of sulphur into the atmosphere to provide an initial cooling. 

“Injection of aerosols is the most potentially controllable SRM technique, because the residence time of sulphur in the atmosphere is relatively short. And there are a number of deployment mechanisms such as aircraft engines.”

But he adds: “The SRM approach has issues around unintended consequences interfering with the climate system. There are a lot of unknowns about the impact on local weather conditions.”

Fox believes that public acceptance of carbon sequestration is likely to be more forthcoming. He says that a Natural Environment Research Council study has shown that air capture through machines is more acceptable to people than tinkering with the climate with SRM. “The public are more comfortable with the concept of air capture and the use of machines to do it,” he says. 

Such machines could one day be deployed in countries that have less fossil fuel-intensive industry than nations in the West and be powered by renewable energy. This could allow nations like Argentina to act to mitigate global emissions and perhaps rack up carbon credits if a global trading scheme is adopted. Fox says: “Countries could participate in air capture and gain credits for removing CO2 from the atmosphere.

“There are quite a few countries, such as in South America, that don’t have highly fossil-fuel intensive industries and that rely on hydroelectric power. But they would like to participate in mitigation of emissions and the use of a geo-engineering technique such as air capture could allow them to do so.” Wind energy in Tierra del Fuego, for instance, could power many carbon sequestration “trees”, earning Argentina carbon credits.

Fox believes that geo-engineering should be researched as part of the United Nations Framework Convention on Climate Change. “It needs to be built into the UNFCCC,” he says. “The initial engineering assessments, and, to build confidence, the validation of the technology, need to be done within the international framework.

“It should be international research feeding into an international initiative. But we would encourage the British government to take a lead on those negotiations. The pace isn’t fast enough.” 

Launder says there are certain areas of potential surface geo-engineering that have yet to be fully explored. One of these might be making the sea more foamy to reflect more solar radiation. “I do think strategies for brightening the oceans hold more potential than some other surface schemes,” he says.

“There are proposals that have been made that could mean creating a foamy surface, with the bubbles reflecting more light. You might say, of course, that as global warming progresses we will get more storms, which will make the sea foamier. I don’t think we want to rely on that.” 

Much more work will have to be done to make any of the above schemes a reality. Shepherd says: “This problem is big enough and serious enough that we need everything we can think of to deal with it. It’s going to be very hard and we will inevitably do too little, too late. I think we’re in for a very bumpy ride.”

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