COPENHAGEN—The controversy at this climate summit revolves around two simple issues: Who cuts? Who pays? Of course, climate change does not distinguish between a ton of carbon dioxide emitted from cutting down a peat forest in Indonesia versus a ton emitted as a result of burning coal in Germany. Therefore, a relatively new term is beginning to stir some controversy here in the Danish capital outside the direct negotations: geoengineering.

That's in part because the "Conference of Parties" negotiations have taken so long. After 17 years, the basic issues remain to be addressed, and overall emissions have grown since 2000—the year enshrined in the United Nations Framework Convention on Climate Change treaty as the peak year of greenhouse gas emissions for the developed world (the U.S. signed this agreement). With little hope of reducing emissions in the near term—some scientists, such as geochemist Wally Broecker of Columbia University think we'll be lucky to stop at concentrations of 550 parts per million in the atmosphere—more radical solutions are on offer: artificial, eternal volcanoes; using saltwater mist to increase cloud cover; even flotillas of mirrors in space.

"Geoengineering is plan B," says oceanographer John Shepherd of the U.K's Royal Society of plans to deliberately tinker with the planet's climate. "It's not to be adopted unless absolutely necessary."

After all, "geoengineering is technically possible," Shepherd adds. But "in most cases, it's still on the backs of envelopes and there are very many things to be concerned about, like environmental impacts."

It's not just environmental impacts from filling the skies with sulfur dioxide to mimic the cooling impact of a massive volcanic eruption, like Mount Pinatubo in 1991, among other plans on offer. "This will have vast human rights implications, on self-determination, on the right to food," says Diana Bronson, program manager at the ETC Group. "We're talking about technologies that would modify the entire planet."

And though building a sulfur dioxide smokestack to the stratosphere is an expensive proposition, there are simpler and cheaper ways to accomplish these ends, including dumping such particles from a helicopter. "It would take 10 Howitzers firing a shell a minute a year to get sulfates into the atmosphere," says Jason Blackstock, an analyst at the International Institute for Applied Systems Analysis. "Fifty to eighty countries in the world are capable of this."

Already, Russian scientist Yuri Izrael has begun to experiment and the Chinese routinely seed clouds to produce rain or snow. The Indians and Germans have conducted scientific testing of dumping iron in the ocean to attempt to promote algae growth and thus carbon sequestration.

"We aren't going back to the climate we had before," says Jane Long, associate director for energy and environment at Lawrence Livermore National Laboratory. "We are going to be managing the environment, not just the climate but also hydrology, soils. We have to learn how to do that."

Of course, there are geoengineering options that are not as dangerous, such as mechanical devices to suck CO2 out of the air. Physicist Klaus Lackner of Columbia University and others are working on such devices and believe they could be accomplished for $300 per metric ton of CO2 removed. And others advocate restoring organic carbon to the soil in the form of so-called biochar (charcoal), which could sequester as much as 900 megatonnes of carbon over the next several decades.

But still questions of governance remain. For example, who will determine the appropriate level for CO2 concentrations in the atmosphere? Freezing Russians or sweltering island states? Who will control the global thermostat?

"Reducing emissions should remain the top priority for the foreseeable future," Shepherd says, "but serious research is needed rather than enthusiasts working in their spare time." Perhaps control of the world's climate shouldn't be trusted to basement tinkerers or scientists.