A sticking plaster for the planet

Alok Jha
guardian.co.uk, Wednesday 21 October 2009 16.30 BST
However impressive someone is, however many excellent and entertaining books they might have sold, never believe anyone who tells you there might be a quick fix to global warming.
It's hard to deny that Steven Levitt, an economist at the University of Chicago, and the journalist Stephen Dubner know a thing or two about applying economics to unlikely situations. In their latest book, Superfreakonomics, the pair take on global warming, and argue that technology is our best bet in dealing with it.
Specifically, they get excited about floating hoses that can shoot aerosols into the upper atmosphere to reflect away sunlight, cooling the Earth by a few degrees.
World-changing the easy way
Where the former World Bank economist Nicholas Stern has calculated the penalty of not dealing with a warming world through fiscal and political policies – and in the process changed the priority the political world gave to the issue – Levitt and Dubner have focused their economic nous on human behaviour. In short, why try to persuade billions of people around the world to change their behaviour, when you could easily persuade a few thousand to knock up a device to deal with it all? Even shorter: let's try geo-engineering.
Geo-engineering is a set of technologies designed for use on a global scale to prevent or slow climate change. It includes everything from sending mirrors into space to reflect away sunlight, to dumping iron into the oceans to encourage the growth of CO2-consuming algae. It was once seen as the preserve of the wacky, but in recent years its supporters have swelled in number to include scores of climate scientists and engineers. The coalition is messy, with a wide variety of opinion on the best techniques and even the merits of using technology to tackle global warming; if there is any consensus emerging, it is simply that it would be good idea to have some big ideas in reserve, a Plan B, in case nothing comes of appeals to personal abstinence and global political will.
Trial balloons
This was the conclusion of a report published last month by the Royal Society. The most comprehensive study on the subject to date, it called for urgent investment to test some of the options, arguing that scientists need to get beyond the simulations and work out whether the potential risks of these technologies outweighed the benefits on these technologies.
"Unless the world community can do better at cutting emissions, we fear we will need additional techniques such as geo-engineering to avoid very dangerous climate change in the future," said John Shepherd of the University of Southampton, who chaired the Royal Society report. He added, however,But the report's chair, John Shepherd of the University of Southampton, said that neither he nor the working group advocated geo-engineering. "Our opinions range from cautious consent to very serious scepticism about these ideas. It is not an alternative to emissions reductions and cannot provide an easy quick fix."
Levitt and Dubner, meanwhile, seem most interested in the work of Nathan Myhrvold, a former chief technology officer at Microsoft. He has set up a company, Intellectual Ventures, that is looking at lifting an 18-mile (29 km) hose into the stratosphere with helium balloons. By pumping sulphur dioxide particles into this region, at a cost of around $20m, the company thinks it could reflect some sunlight away from the Earth's surface.
"The theory behind it is an attempt to mimic what happens with very large volcanoes that inject material into the stratosphere," says Naomi Vaughan, a climate scientist at the University of East Anglia (UEA).
"These are volcanoes that occur near the tropics and the clear example that everyone looks at is Mount Pinatubo, which erupted in June 1991."
Pinatubo, in the Phillipines, threw 10m tonnes of sulphate particles into the atmosphere as it erupted, lowering global temperatures by 0.5°C the following year. As for how much sulphur aerosol would be needed to achieve the effect artificially, estimates range from 1.5m to 5m tonnes. That's to offset the warming from a doubling of current levels of CO2 in the atmosphere. Power plants produce and pour about 35m to 40m tonnes of sulphur compounds a year into the troposphere (from the ground to 11 miles up).
"A number of factors inform this range of estimates," says Vaughan. "A key one is particle size: the smaller the particle size the less mass of sulphur is needed, but if the particles are too small they can 'glob' together and fall out of the stratosphere quicker." Injections would have to be replenished every two to three years.
Earlier this year, Vaughan published a paper with UEA colleague Tim Lenton in the journal Atmospheric Chemistry and Physics Discussions, comparing different schemes to cool the Earth. They concluded that stratospheric aerosols had by far the greatest potential to combat warming in the timescale to 2050, given their relatively low cost and high efficiency.
But they also raised several concerns. Aside from unpredictable changes in the amount and pattern of global rainfall, stratospheric aerosols would two decades ago, the ozone hole over the Antarctic has been shrinking. In a study published last year in Science, Simone Tilmes of the National Center for Atmospheric Research in Boulder found that injecting stratospheric aerosols into the upper atmosphere would delay the ozone layer's recovery by 30 to 70 years.
Perhaps the biggest issue, however, is that this kind of "solar radiation management" does not do anything to tackle the culprit behind global warming: carbon dioxide. Such techniques – other proposals include throwing salt water into the air to enhance cloud cover and painting roofs white to reflect away sunlight – mask the core problem rather than permanently dealing with it. And they would need to be in place for ever.
"As soon as you stop any type of solar radiation management, the rate of warming is extremely fast – the system readjusts," says Vaughan. "Rather than having steady warming as our CO2 levels go up, if you bring the intervention in so the world cools, and then stop it 20 years down the line, you get a rapid warming back up to the level that it would have been if you'd never had that intervention."
So, as well as solar radiation management, geo-engineers would need to come up with ways of removing carbon dioxide from the atmosphere. There are good ideas for how to do this. Some suggest stimulating algae in the oceans could sequester large amounts of CO2, while Klaus Lackner at Columbia University wants to build huge "artificial trees" to directly suck CO2 from the air. But all are complex to engineer.
Stratospheric aerosols are easier – but making an 18-mile hose defy gravity still won't be simple. "I think they're going to do it by having 100 balloons lifting it up or something," says John Loughhead, executive director of the UK Energy Research Centre. " We shouldn't underestimate how difficult it will be to get that up there.
"What they put forward as a possible way needs an enormous amount of work to see if it can be done practically."
Loughhead doesn't discount the effort but he warns against the temptation to focus attention on just one technology. "The problem that we face with climate and carbon is of such a scale and in a system of such complexity that to believe anything will be a silver bullet is naïve. We need to explore all the possible routes because they will all advantages and disadvantages and we will probably have to apply them all in some way ultimately to get to where we want to be."