THEY want to save the planet. The engineers who brought us cloud seeding and plans to warm Siberia by melting the Arctic now say they can stave off global warming by shading the planet with tiny metal balloons or burying greenhouse gas on the ocean floor. And climate scientists, depressed by the failure of politicians to cut emissions of greenhouse gases, are starting to take a serious interest.
The idea of global “mega-engineering” technology to combat global warming sounds fanciful, but the need for it is not. CO2 levels are forecast to double from pre-industrial levels within half a century. Until very recently climate scientists mostly dismissed the idea of engineering our way out of the problem. Information about the likely cost, effectiveness and potential ecological impacts of such schemes was scant. Many worried that even discussing the proposed technologies would distract politicians from the issue of reducing greenhouse gas emissions.
But that view is starting to change. Even senior climate scientists such as Bert Bolin, former chairman of the UN’s Intergovernmental Panel on Climate Change, have recently argued that mega-engineering may have to be called in to stave off global warming. They see two reasons for this change of heart. First, the continued political dithering about the Kyoto Protocol, which shows little sign of bringing about the reductions in emissions scientists had hoped for. And second, the growing fear among scientists that climate change may happen more abruptly than conventional climate models predict. Earlier this month, the US Senate Commerce, Science, and Transportation Committee approved a bill earmarking $60 million for research into this issue. A sudden shut-down of the Gulf Stream, for example, the rapid obliteration of the Amazon rainforest or some other catastrophe could mean the world needs a quick fix to halt global warming within years rather than decades.
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Concerns like these prompted scientists to hold a conference in Cambridge, UK, in January to discuss the proposed technologies. “I fully expect that one or more will be deployed in the near future,” says one of the conference organisers Ed Boyle, an oceanographer at the Massachusetts Institute of Technology. The technologies come in two kinds. One aims to head off the greenhouse effect by capturing CO2 and storing it out of harm’s way – either in geological structures like salt domes and old oil wells, or deep in the ocean. The other would allow CO2 to accumulate in the atmosphere, but put the brakes on warming, either by shading the Earth from the sun or by engineering the environment to reflect more solar radiation back into space.
Changing the planet’s reflectivity – its albedo – would be the fastest way to halt global warming, and ideas on how to do this have a long and imaginative history. In the mid-1960s, US scientists discussed spreading billions of small reflecting objects, such as white golf balls, across the tropical oceans. In 1982, Soviet scientist Mikhail Budyko suggested mimicking volcanic eruptions by throwing light-reflecting sulphate particles into the stratosphere. He reckoned 10 million tonnes of sulphate sprayed from high-flying aircraft each year could scatter 1 per cent of solar radiation and counter the effect of a doubling of CO2 levels in the atmosphere.
Sky balloons
There things rested until the late Edward Teller, father of the hydrogen bomb, suggested a similar space-age shield against climate change. He proposed putting shards of metal or specially made “optical resonant scatterers”, which reflect light of particular wavelengths, into the stratosphere. Most recently, Teller, Lowell Wood and others at the Lawrence Livermore National Laboratory in California argued that just a million tonnes of tiny aluminium balloons, each around 4 millimetres across, filled with hydrogen and floated into the stratosphere, could do the same job for as little as a billion dollars a year.
Another approach proposed by Wood is to assemble a giant diaphanous mirror in space a thousand kilometres across and park it between the sun and the Earth to reflect solar radiation away from our atmosphere. Some 3000 tonnes of shield could compensate for a doubling of CO2 levels. The cost could run into hundreds of billions of dollars, but it would be a far more permanent solution than optical chaff in the stratosphere, Wood told the Cambridge meeting.
If golf balls and space mirrors prove to be too far-fetched, John Latham of the US government’s National Center for Atmospheric Research in Boulder, Colorado, has suggested a more down-to-earth option: making clouds whiter. This is a variation on the old idea of “seeding” clouds to make rain. Water droplets form in clouds as water vapour gathers around hard particles called “cloud condensation nuclei”. To seed clouds, people add artificial particles to make more droplets. But if they add too many nuclei the droplets multiply, but never get big enough to fall as rain. Latham’s idea is to deliberately add too many particles, packing clouds with droplets to boost their whiteness and reflectivity.
He calculates that doubling the number of droplets in clouds over all the world’s oceans would shut down several decades of global warming. Ingeniously, he proposes doing this by deploying giant wind-powered machines to fling salt spray from the sea into the air. He suggests that a machine similar to the one being developed by Scottish inventor Stephen Salter of the University of Edinburgh, UK, might do the trick. Salter has created a prototype “spray turbine” that looks rather like a giant egg whisk, originally with the aim of seeding clouds to make rain. A full-size version would be 70 metres high, and hundreds of them across the oceans could whiten clouds across thousands of kilometres, says Latham, who plans a pilot experiment within two years. But the enterprise would need to be huge and constant, since clouds only last a few days before they disappear.
Practicality isn’t the only issue facing engineers who plan to alter albedo, however. Tinkering with something as crucial and poorly understood as solar radiation could have dramatic and unforeseen consequences for our global climate and life-support systems.
There is, for a start, the small matter of the colour of the sky. Wood’s “optical chaff” would alter both the quality of sunlight and the radiation balance in the lower atmosphere. It might, for instance, make the sky less blue, giving new meaning to the old phrase about “blue-sky research”. But one more serious casualty could be the stratosphere. Under the Wood strategy, its temperature would fall both because of reduced solar radiation and because accumulating CO2 would trap ever more of the available heat in the lower atmosphere. This would create ideal conditions for the rapid destruction of the ozone layer.
Wood counters that his optical chaff would filter out UV radiation. But that raises another issue. Even UV radiation has its role in atmospheric chemistry. Peter Liss of the University of East Anglia in Norwich, UK, warns that UV manufactures hydroxyl, the atmosphere’s chemical cleansing agent. Lose too much UV and all sorts of polluting gases – from greenhouse gases such as methane to the agents of smog and acid rain – would accumulate to dangerous levels. We could soon be choking under our planetary parasol.
The ability to alter Earth’s albedo would also give us an unprecedented level of control over our planet’s temperature. “Basically it means we can turn the planetary temperature to any level you wish,” says Wood. “If necessary, we could stop a new ice age.” Sure, says his critics – or start one.
Uniquely too, albedo manipulation gives humanity the chance to adjust planetary temperatures and CO2 independently. We could have atmospheric CO2 levels soaring to twice, four or even eight times current levels, while global temperatures are held in check. Wood sees that as a huge bonus. More CO2 makes plants grow faster, meaning that poor tropical farmers would get bumper crops. “The biggest free lunch in history,” he says. Millions of lives could be saved from famine, and at a fraction of the cost of cutting CO2 emissions.
Mopping up
Many crop scientists would take issue with his arguments, and many atmospheric scientists are equally unimpressed. “I find the willingness of some to monkey around with a system as complex and poorly understood as the Earth’s climate rather appalling,” says Boyle. But James Lovelock, environmentalist and inventor of the Gaia theory, is less squeamish. “I am one of the minority of greens who think the cure to man-made climate change lies in engineering, not in abandoning it.”
At the very least, altering the planet’s albedo runs a serious risk of generating planet-wide and potentially grave consequences.The alternative, namely reducing CO2 levels, doesn’t suffer from these problems. Carbon-capturing is essentially an attempt to maintain the planetary status quo. And although it would take longer to have an effect on warming, methods of capturing and burying carbon dioxide are more prosaic and better developed, meaning that this kind of mega-engineering is closer to becoming reality.
The basic idea is simple: first find a stream of industrial gases venting to the atmosphere and rich in CO2 – waste gases from a power station, refinery or cement works, or natural gas coming out of the ground, then separate out the CO2 and bury it somewhere.
Some companies in the US already do this on a small scale, extracting CO2 from natural gas to create fuels richer in hydrogen. Many more would do it if there were government incentives. In Norway, the state oil company Statoil has been escaping the country’s carbon tax for the past seven years by removing CO2 from North Sea gas and pouring it straight back beneath the seabed into voids left behind by the gas extraction. Some 70 million tonnes of CO2 have so far been buried. That is only 1 per cent of annual global emissions, but it’s a start.
Julio Friedmann, a former geologist for ExxonMobil who is now at the University of Maryland, says geological carbon “sequestration” could be widespread within a decade. “All we have to do is scale it up to the billion-tonne business.” His grand plan is for thousands of “zero-emission power plants” across the world that burn cheap fossil fuels but capture the CO2 from the stack. They may add only 10 per cent to the cost of electricity, he says – “cheaper than converting to wind power”.
Friedmann estimates that worldwide, there may be space underground for safe storage of up to 1 trillion tonnes of CO2. That is equivalent to 150 years of current global emissions, and is hundreds of times as great as what you might achieve by planting trees to soak up CO2.
Another option, with an even bigger theoretical holding capacity, is pouring CO2 into the deep ocean as a gas or liquid. On the face of it, if stored sufficiently far down, water currents and huge pressure should keep it from returning to the atmosphere. But will they?
Modelling by Ken Caldeira of Lawrence Livermore suggests about 20 per cent of the CO2 will return to the atmosphere within around 300 years. That doesn’t sound too bad: 80 per cent stays put. Except that a similar proportion of the CO2 pumped into the atmosphere from power stations and car exhausts ends up absorbed by the ocean anyway, and on a similar timescale. In the long run, the atmosphere and oceans share out the CO2, meaning that this would only be a short-term measure. There may be ways of keeping the gas down longer, such as encasing it in giant plastic bags on the floor of the deep ocean or injecting it under the floating ice of the West Antarctic ice cap. But ultimately burying it in the ocean buys us some breathing space, no more.
Alternatively, we could increase the ocean’s capacity to mop up excess CO2. Fertilising the surface of the ocean with iron can encourage plumes of plankton to grow and absorb CO2. This will probably work best in the Southern Ocean, which is desperately short of iron through some biogeochemical quirk. Sprinkle some iron filings into the water and plankton “blooms”. As the plankton die and sink to the ocean depths, the CO2 is packed away out of harm’s way for hundreds of years.
It’s cheap, and on the face of it is easy to do. But as yet there is no certainty about the fate of the CO2. And at about half a billion tonnes a year, even the theoretical capacity of the Southern Ocean to absorb CO2 is small. The Cambridge meeting voted it the least likely technology to succeed.
Even more ambitious is a plan by Klaus Lackner of Columbia University in New York to dot the landscape with windmill-sized factories to strip the wind of CO2. His windmills would waft air across a CO2-absorbing chemical such as calcium hydroxide. Every community could have one to remove as much CO2 as they emit from sources such as vehicles, where the CO2 cannot easily be captured at source. Lackner plans to builder a trailer-truck-sized prototype soon. Running costs are horrendous, he admits – maybe $100 per tonne of carbon. But ultimately this might do something other technologies don’t. Stripping CO2 from the air could one day reduce levels of the gas by as much as the world wants – even down to pre-industrial levels.
Mopping up CO2 from our atmosphere sounds like an attractive prospect, but it has its share of problems too. Public acceptance is one. Environmentalists have already torpedoed a US government project off Hawaii to explore the ecological downside of ocean burial, claiming it would damage the environment. Meanwhile, Friedmann fears people will think his geological sequestration sounds too much like burying nuclear waste.
And there are genuine concerns about safety. At Lake Nyos in Cameroon 18 years ago, a huge bubble of CO2 escaped from the bottom of a lake in a volcanic crater and wafted across the countryside, asphyxiating some 1700 people. In the longer term, ocean burial would inevitably acidify the deep ocean, which would have a major impact on marine life.
Given these concerns, will mega-engineering really be able to solve our climate problems? While some researchers think it is the answer, most believe it will only be part of the solution, buying us precious time while we reduce our CO2 emissions. Of all the technologies, capturing CO2 is most likely to attract the money needed to put it into practice. This is because the Kyoto protocol rules may one day allow companies to obtain tradeable carbon credits from doing this. Albedo engineering is more blue-sky, partly because the research is at an earlier stage, and partly because it is not clear how anyone would make money out of it.
Even if these technologies were to work according to plan, we would still face the daunting prospect of what to do with the control they gave us over Earth’s climate. Lovelock sees being a planetary manipulator as something akin to being a doctor. He wants “a Hippocratic oath for macro-engineering”. All well and good. But once built, technologies such as solar scatterers would also be fearsome weapons in the hands of a global superpower, as well as being the prime terrorist target of all time. Whose hand would be on the global thermostat?
