WASHINGTON -- Faced with the potentially devastating consequences of climate change--including sea level rise and an ice-free Arctic--some scientists and policy experts have begun to consider an equally drastic countermeasure: geoengineering.
By physically altering the planet on a global scale, geoengineering projects would theoretically offset warming caused by the build-up of carbon dioxide in the atmosphere. The concept was dismissed as fringe science when it was first introduced in the 1960s. Now, what once seemed like science fiction is not only being deemed feasible, but necessary, said experts at a panel convened here Tuesday by the American Enterprise Institute for Public Policy Research, a conservative think tank.
One popular geoengineering scenario is to create an artificial volcano. Thomas Wigley, an expert on climate change based at the National Center for Atmospheric Research in Boulder, Colo., has created computer simulations that replicate the 1991 "Mount Pinatubo effect"--a temporary cooling period created by the launch of 20 million tons of sulfur dioxide into the stratosphere.
Wigley proposes mimicking the natural process by injecting sulfur dioxide or hydrogen sulfide into the same region, 60,000 to 70,000 ft. above the earth's surface. The compound would react to form a cloud of sulfuric acid droplets that would in turn reflect sunlight and cool the globe. Exactly how the material would be delivered isn't clear--cannons, balloons and high-flying military planes are some "highly speculative" options, he says.
Such a scheme isn't cheap. Depending on the frequency, delivery system and whom you talk to, estimates vary wildly from $1 billion to $50 billion a year. Whether it's worth the high price tag is still hotly debated.
Geoengineering would buy time for societies as they work on the technological revolution necessary to reduce carbon dioxide emissions, says Scott Barrett, an economist specializing in environment and international political economy at the School of Advanced International Studies at Johns Hopkins University in Baltimore.
"That's an excuse to conduct business as usual," says Alan Robock, a meteorologist at Rutgers University in New Brunswick, N.J. "It takes political will to lower carbon dioxide emissions. There are plenty of solutions already available."
Robock has also run the numbers on the artificial volcano scenario. Matching the Mount Pinatubo effect would involve launching 5 million tons of sulfur dioxide into the atmosphere every year for about four years. "That's going to be very expensive and locally polluting," he says.
Volcanic eruptions also destroy ozone. Geoengineering schemes that blast sulfur-containing compounds into the atmosphere could hinder the repair of the ozone hole by up to 70 years. The hole has been on the mend; it is estimated that it will disappear by the mid-21st century.
Both Robock's and Wigley's models suggest that this approach could reduce rainfall globally. Mount Pinatubo triggered lower rainfall, soil moisture and river flow in many regions. Volcanic eruptions at tropical latitudes cause warmer winters in the Northern Hemisphere, and eruptions at high latitudes can weaken the Asian and African monsoons.
There are other back-of-the-envelope geoengineering options for chilling the earth, including tinkering with cloud chemistry to make clouds more reflective. One such strategy involves droplet injection ships that essentially suck up seawater and shoot it into the clouds, altering the condensation nuclei. Another plan is to create artificial trees that extract carbon dioxide directly from the atmosphere.
Astronomer Roger Angel, of the University of Arizona, has proposed launching into orbit trillions of small lenses that would bend sunlight away from the planet. On the opposite end of the spectrum is the ultra-low-tech approach of painting rooftops white to reflect sunlight.
But even if geoengineering succeeds at turning down the world's temperature, it doesn't address other consequences of rising levels of greenhouse gases. As the oceans absorb carbon dioxide, for example, seawater will become more acidic--destroying coral reefs and marine creatures encased in calcium carbonate.
Jay Gulledge, an ecologist specializing in the carbon cycle at the Pew Center on Global Climate Change, points out that if geoengineering efforts produce negative effects "there's no guarantee that the climate will just switch back." The climate may shift permanently--as it seems to have done in the Sahel where rainfall has decreased, lakes have dried up and river levels have dropped, and in the North Pacific where changes in wind patterns have become more El Nino-like.
This week, the Senate is debating a climate change bill that would cap greenhouse gas emissions by two-thirds by 2050, and force polluters to buy permits to release carbon dioxide. Critics argue that promoting geoengineering now could undermine the need for such legislation.
In the future, they say, successful geoengineering projects could provide a false sense of security, and diminish the urgency of reducing greenhouse gas emissions. And should the fix unexpectedly fail, high CO2 levels from unabated emissions could trigger the worst-case scenario for global warming.
To be fair, no one on Tuesday's panel proposed geoengineering as a silver bullet, but something to be considered among a suite of steps that include reducing emissions and increasing R&D for carbon sequestration.
"Anyone who says that geoengineering offers a policy solution to climate change is decades ahead of the science," Gulledge says. "And that's not a safe place to be."
The 1991 eruption of Mount Pinatubo in the Philippines sent 20 million tons of sulfur dioxide back into the stratosphere. Now scientists are wrestling over a potential delivery system for an artificial recreation of the natural effect--and over how much it would cost. (Photograph Courtesy of USGS/Cascades Volcano Observatory)