Two facts about climate change have become increasingly clear: New efforts to constrain global greenhouse gas emissions are likely within the next few years -- and their effect on the climate will be modest at best. Rapidly rising emissions in the developing world will swamp whatever reductions the United States, Europe and Japan may make. Atmospheric concentrations of greenhouse gases will continue to rise for decades to come, and warming will continue well into the next century.
What will happen? We may hope that the effects will be modest, but there is real risk that they will be very serious, at least for the most vulnerable nations. Some scientists warn of the possibility of abrupt climate change, with unpredictable but conceivably catastrophic consequences. Most troubling, by the time there are unmistakable signs of disaster, even a crash course of emissions reductions will be too late.
Policymakers have only considered two responses to climate change: cutting emissions, and adaptation -- that is, learning to live with a warmer planet. There is, however, a third possible strategy, one that could be fast, effective and affordable -- but that is being ignored. This idea is commonly known as geo-engineering.
The Earth is warmed by two forces: solar radiation, which enters the atmosphere, and the greenhouse gases that trap it there. There are two ways to cool the planet: reduce greenhouse gases or reduce the amount of solar radiation that reaches the Earth's surface. Or both. If we cannot do enough of the first, we must consider whether the second option -- geo-engineering -- is feasible.
In fact, geo-engineering could be surprisingly simple. Scientists noted that the 1991 eruption of Mt. Pinatubo in the Philippines cooled the planet for two to three years by roughly half a degree Celsius. There are various ways of artificially reproducing this effect. A small amount of ultra-fine sulfur particles injected into the upper atmosphere could deflect 1% or 2% of incoming sunlight -- almost unnoticeable, but enough to cancel out the warming expected to occur this century. Or a fleet of ships spraying seawater into the air might achieve the same general effect by increasing the density of (and thereby the reflectivity of) low-altitude marine clouds. Even painting the roofs of buildings white would be a low-tech way of reflecting a little sunlight.
A growing number of leading scientists and environmental economists take the idea of geo-engineering very seriously. The National Academy of Sciences, NASA and the Department of Energy have concluded that geo-engineering could be, in the words of the National Academy, "feasible, economical and capable."
The question for policymakers is not whether to deploy a geo-engineering system immediately or to make it the primary focus of climate policy. Rather, it is whether to make a serious investment in the research and development needed to accurately evaluate its risks and rewards. Unfortunately, the Bush administration has declined to pursue such research, although it would cost only a small fraction of the $3 billion the federal government spends annually on developing new technologies to reduce emissions.
Why the reluctance to study this idea? Fear. Fear that geo-engineering would not work, and fear that it would.
There are two concerns about geo-engineering. One is the risk of unintended consequences. Scientists note that sulfur particles could cause stratospheric ozone depletion, although the evidence from Pinatubo suggests that this effect would be modest. Others fear possible disruption of regional climates, such as the Asian monsoon. Most scientists studying geo-engineering believe that these side effects are not likely to be nearly as dangerous as uncontrolled warming, but much more research is needed.
Fear that geo-engineering might work, however, is the reason some people reject, or are reluctant to even openly discuss, this idea. Critics worry that geo-engineering could be used as an excuse to continue unchecked emissions forever. Within the last two years, three high-level conferences have explored geo-engineering; each was held behind closed doors. One premier university was too frightened to even do that. There have been calls for boycotts of the research or, failing that, strict international regulations.
This concern is badly misplaced. Geo-engineering is a remarkable idea with tremendous potential, but it is neither a permanent nor a perfect solution to warming. There are risks to and, more important, limitations on what it can do. Even among its most enthusiastic advocates, no one calls for a policy of "geo-engineering forever, emissions reductions never." Geo-engineering would be a complement to, rather than a substitute for, a long-term program to transition to a zero-emissions economy.