CAMBRIDGE, England -- At a meeting here this month top climate scientists and technologists from both sides of the Atlantic reached an extraordinary consensus: Ideas for curing global warming that were once dismissed as screwball now need to be taken seriously.
Technical fixes like filling the stratosphere with billions of silver balloons to reflect the sun's rays, or spraying the oceans with iron to make them suck up the gases causing global warming, should be developed as a safety net, they said. Some even felt the technology should be adopted regardless of need, because it would create a better world in which we could twiddle with the planet's temperature like a domestic thermostat.
"I fully expect that one or more of these technologies will be deployed in the near future," said Ed Boyle of MIT, a co-organizer of the conference. "In the event of an unanticipated climatic catastrophe, we may need a rapid fix."
Many of the two-dozen researchers concluded that they shouldn't just sit back and wait for their governments to belatedly realize the earth is getting too hot. But others feared that developing a safety net would send the wrong signal to politicians.
About to board a plane to discuss climate change with the Bush administration last week, Britain's chief scientist, David King (who recently described global warming as a bigger threat than terrorism), said: "I am in favor of having every weapon at our disposal to fight climate change. My only reservation is that you might provide a fig leaf for those who say we don't have to bother to reduce emissions of greenhouse gases. That still has to be the first priority."
The technologies come in two types. The first aims to capture and bury pollution gases such as carbon dioxide (CO2) so that they do not build up in the atmosphere, where they trap heat and raise temperatures. The second shades the earth from solar radiation, keeping us cool.
So far the world has heard more about the first type. The US Department of Energy has a research program on capturing CO2 in waste gas from fuel processing plants. And geologists from American oil and gas companies have been investigating ways to bury compressed CO2 underground.
Julio Friedmann, a former ExxonMobil geologist now at the University of Maryland, said: "We have the technology. All we have to do now is scale it up to a billion-ton global business."
Worldwide, there may be space underground for a trillion tons of carbon -- or 150 years of current global emissions. There could be even more space for pouring compressed CO2 into the deep ocean, said Ken Caldeira of the Lawrence Livermore National Laboratory in California. Some will bubble back to the surface, but 80 percent should stay there permanently.
But burying CO2, whether beneath the ground or the waves, is likely to face environmental opposition. What if the CO2 leaked? Eighteen years ago, 1,700 people in the African state of Cameroon died of asphyxiation after a huge bubble of natural carbon dioxide erupted from Lake Nyos.
Meanwhile, as Caldeira admits, nobody quite knows the biological consequences of pouring CO2 into the ocean. Two years ago, environmentalists and fishermen scuttled a US government research project off the coast of Hawaii that had been designed to find out.
Instead of stripping CO2 from waste, Klaus Lackner from Columbia University in New York offered the prospect of designing a windmill-sized machine that could scrub CO2 out of the air by passing it over a chemical like limewater that would absorb the gas. It's too costly for now, he admits, but one day, we might place such machines in every town to bring CO2 concentrations down to pre-industrial levels -- the ultimate atmospheric cleanup.
Others, more immediately, wanted to use biology to soak up CO2. Planting trees as a "carbon sink" is already standard practice, but how about doing the same in the oceans?
Victor Smetacek of the Alfred-Wegener Institute in Bremerhaven, Germany, has tried sprinkling the southern ocean round Antarctica with iron filings. Plankton grows much faster there with a bit of added iron. As it grows, it absorbs more CO2, which gets replaced from the atmosphere.
Smetacek thinks ocean currents then take the plankton to the ocean depths, burying the CO2 forever. But others are not so sure. This "cheap and easy" system, which has recently attracted a lot of commercial interest, was voted the carbon-capturing technology least likely to succeed by the Cambridge meeting.
Instead, the scientists backed more way-out systems for reflecting the sun's rays back into space. Plan A would float thousands of bubble-making machines across the world's oceans to send huge amounts of salt spray into the atmosphere. The trillions of tiny droplets would make the clouds bigger, whiter, and more reflective -- enough, in theory, to shut down several decades worth of global warming.
Plan B would flood the stratosphere with billions of tiny metal-coated balloons, "optical chaff" to backscatter the sun's rays. Most sophisticated of all, Plan C would assemble giant mirrors in orbit, ready to be positioned at will by a global climate controller.
Reconfigured to reflect solar heating onto the earth, the mirrors could in a future millennium halt the next ice age, said Lowell Wood, of Lawrence Livermore.
Controlling the sun's rays also for the first time offers us the chance to independently manipulate temperatures and CO2. Wood argued that crops would grow faster in a CO2-fertilized atmosphere, without the downside of droughts caused by rising temperatures. Millions of people could be better fed.
The question marks surrounding such technologies are, of course, legion.
"I find the willingness of some to monkey around with a system as complex and poorly understood as the earth's climate rather appalling," said MIT's Boyle.
Even if the technology worked as billed, who would be in charge? Who would tilt the solar reflectors or deploy the optical chaff or sprinkle the iron? Who would decide what the optimal global temperature should be, and whether to tilt the mirrors to warm Siberia a bit, or cool New England? The scientists adjourned without deciding whose hand should be on the global thermostat.