Geoengineering: A Quick, Clean Fix?

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David Harlow / U.S. Geological Survey / TIME-LIFE Pictures / Getty Images

Cool cloud The eruption of Mount Pinatubo in 1991

In the course of a long weekend in 1991, the Philippines' Mount Pinatubo volcano injected enough sulfur dioxide into the stratosphere to temporarily reduce the sunlight reaching the earth's surface by about 10%. As a result, global temperatures dropped by an average of 0.5 degrees C over the next 18 months. Turns out the lesson nature taught us that weekend has not been wasted; it may help us combat global warming.

The late climate scientist Stephen Schneider used to compare the modern world's dependence on fossil fuels to a drug addict's need for heroin. The habit is dangerous and unhealthy, yet almost impossible to break. Certainly, that's the lesson to be drawn from the inability of the world's governments to reduce carbon emissions over the past 20 years. So what are we to do? The solution for addiction often involves palliatives like methadone for a heroin junkie, and so it may be for our addiction to fossil fuels. Our planetary methadone, Schneider said, may be geoengineering — or the attempt to replicate the effect Mount Pinatubo had on the climate in 1991.

Geoengineering, the deliberate modification of the environment to suit human needs, has long been regarded as the height of hubris by many people and most environmentalists. We are a long way from fully understanding how the climate system works. Who's to say that in our efforts to tinker with it we won't make things worse? These are valid concerns, and geoengineering should be approached with caution. But it is increasingly hard to see how we are going to solve global warming without some reliance on it. Indeed, after a lengthy study (in which I participated) the U.S. Government Accountability Office just issued a report about geoengineering that makes this very point.

However hard we try, it will take us decades to make the transition from a carbon-based economy to one powered by new energy technologies. In the meantime, it is possible that global warming may approach a point beyond which there would be no going back. This is where geoengineering comes in: it's not a long-term solution but a way to keep the earth from overheating while we wait for truly efficient and affordable green-energy technologies to come on line.

Can geoengineering really do the job? The evidence is all around us. Modern global warming is itself evidence of inadvertent geoengineering, the result of all that carbon dioxide and other greenhouse gases we've been pumping into the atmosphere for a century or so. But it was the Pinatubo eruption that provided a modern-day example of geoengineering's potential. Scientists studying the eruption wondered if they could do the same thing deliberately. The eventual result was an ingenious technology known as stratospheric aerosol injection, or SAI, which today is on the verge of providing us with a potentially powerful tool to cool the planet.

Under a plan currently being developed by Nathan Myhrvold's Intellectual Ventures, sulfur dioxide would be pumped up a 25-km-long pipe suspended by high-altitude balloons, then sprayed out into the stratosphere. Myhrvold, formerly Microsoft's chief technology officer, says just one such pipe less than a foot in diameter could do the job for the entire northern hemisphere — at a cost of less than $1 billion. More research is needed, however, to establish the technology's ramifications, including its effects on ozone levels.

An even more promising solution is something called marine cloud-whitening. The idea is that if you fill the air with tiny particles around which water vapor can condense, you'll get denser, whiter clouds that will reflect more solar energy back into space, thus cooling the planet. Together with John Latham of the National Center for Atmospheric Research, the University of Edinburgh's Stephen Salter has designed a fleet of remote-controlled wind-powered catamarans that would do just that — spraying tiny particles of seawater into midocean clouds, brightening them just enough to keep temperatures down.

SAI and marine cloud-whitening are just two of many possible geoengineering projects. Others range from putting giant mirrors in space to planting billions of trees. What they all have in common is the potential to have a large and immediate impact on global temperatures at relatively low cost. None represent any kind of permanent solution to climate change. They are, as many critics have pointed out, merely Band-Aids. But Band-Aids have their uses. The only real solution to global warming is to end our dependency on fossil fuels. Doing this will take time — time that geoengineering can give us. We'd be mad not to take it seriously.

Lomborg is the author of The Skeptical Environmentalist and Cool It, head of the Copenhagen Consensus Center and adjunct professor at Copenhagen Business School. His new film, Cool It, opened on Nov. 12

This article originally appeared in the November 22, 2010 issue of TIME Europe.