Engineering the Climate: What If It's Not Possible to Cut Greenhouse Gas Emissions Enough to Thwart Global Warming? Samuel Thernstrom Is Investigating a Potential Solution-Geoengineering

Article excerpt

Q What is geoengineering?

A Many scientists and policymakers have become increasingly pessimistic about the prospects in the near future of sharply reducing global greenhouse gas emissions, so scholars have begun to consider whether there might be other ways to counteract global warming, particularly if it proves to be severe. "Geoengineering" is the most common term for efforts to intentionally change the Earth's environment in ways that would compensate for the effects of elevated greenhouse gas concentrations. "Climate engineering" might be a better term for this concept.

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The basic idea is quite simple. The Earth is warmed by two forces: solar radiation, which enters the atmosphere, and the greenhouse gases that trap it there. There are two possible ways to cool the planet, therefore: reduce greenhouse gases or reduce the amount of solar radiation that reaches the Earth's surface. If we can't cut greenhouse gas emissions quickly enough, it makes sense to think about the other source of warming, solar radiation. Reflecting just a small fraction of the incoming sunlight--roughly 2 percent--would be enough to offset the warming effects that we are likely to experience in this century.

Q Could we really do that? How do you know it would work?

A It might be premature to say that we know it would work--but the evidence we have so far indicates that it would. The National Academy of Sciences, NASA, the Department of Energy, and several leading academic scientists have studied geoengineering and concluded that it could be (as the National Academy put it) "feasible, economical, and capable."

The science is still in its infancy, and will remain so until there are field experiments to test the theories and models that scientists are working with today. But Mother Nature has conducted some dramatic experiments that provide a relatively crude but clearly effective demonstration of the basic concept. The 1991 eruption of Mt. Pinatubo in the Philippines, for example, cooled the planet for at least a year by roughly half a degree Celsius. The question for scientists and engineers is how we could artificially reproduce that effect.

Q What kinds of geoengineering projects could be considered?

A There are a few different ideas, but the simplest and most commonly discussed one among scientists is mimicking the effects of a Mt. Pinatubo-type volcanic eruption by distributing some kind of ultra-fine particles, such as sulfur, in the upper atmosphere. The particles would block enough incoming sunlight to cool the planet and counteract the effects of warming. Such a system could be tested and initially deployed over the Arctic. If results were promising, it could be expanded; if there were undesirable side-effects, the particles would quickly fall to earth once the system was discontinued.

An intriguing idea has been proposed by two British scientists, John Latham, an atmospheric physicist, and Stephen Salter, an engineer. Rather than look to volcanoes as the cooling force to be emulated, they noted that low-altitude marine stratocumuli clouds also reflect sunlight. The reflective abilities of these clouds, which cover about 25 percent of the world's oceans, could he enhanced by a feet of ships that would spray a fine mist of seawater into the air. Latham and Salter calculate that increasing the reflectivity of those clouds by about 10 percent would be enough to counteract the warming effect of elevated greenhouse gas concentrations.

A much more low-tech way of reflecting some sunlight would be to paint the roofs of buildings white. A provocative new study from three scientists in California calculates that painting 1,000 square feet of roof white would reflect enough sunlight to counteract the warming effects of 10 tons of carbon dioxide. Light-colored pavement can also reflect sunlight. If implemented widely throughout the tropical and temperate regions of the world, this study calculates that enough sunlight could be reflected to offset 44 gigatons of C[O. …