2010 has been a bad year for climate, and an even worse year for climate policy. But for that very reason, it’s been a good year for geoengineering—the notion that humans can deliberately manipulate the climate and cool the earth.

Official Washington is starting to take geoengineering seriously: The Government Accountability Office and a bipartisan task force of experts convened by the New America Foundation will soon report on geoengineering. Bill Gates has invested in geoengineering research. Environmental groups–notably Steven Hamburg, the chief scientist of Environmental Defense Fund–have engaged in the conversation. On a parochial note, at FORTUNE’s Brainstorm Green conference last spring, Stewart Brand talked about why geoengineering is important, to a rapt audience that included Bill Ford and Lee Scott.

David Keith

David Keith, a leading scholar of geoengineering who administers Gates’ $4.6 million grant with  with Stanford climate scientist Ken Caldeira, also spoke at Brainstorm Green. So I was pleased to have a chance to reconnect with him at the excellent annual conference run by the Society of Environmental Journalists at the University of Montana in Missoula.  I expected him to be pleased by the momentum gathering behind  geoengineering lately, but I was wrong.

“I think things are moving too fast,” David told me. “Research programs can be killed by spending too much money too fast.” Besides, he said, people need time to wrap their head around geoenginnering. (Juliet Eilperin of The Washington Post recently described it as playing God with the weather. ) “This is a topic—the first time people hear about it, they have wild ideas,” he said.

As I’ve written before – see this, this and this – geoengineering raises a host of thorny ethical, political and governance issues. Who gets to control the earth’s thermostat? Who decides if and when to deploy geoengineering techniques? Which should be used?

At SEJ, David was on a panel with Dane Scott, director of the center for ethics at the University of Montana, and journalist Eli Kintisch, author of a recent book about geoengineering called Hack the Planet. They all seemed to agree that the technology to cool the earth now exists—either by reflecting sunlight back into the sky, an approach known as solar radiation management, or by capturing carbon dioxide from the air. (Keith has a for-profit startup called Carbon Engineering designed to do just that.) They also agreed that the moral ethical issues surrounding geoengineering are daunting.

All also said the topic deserves further research. Small government-funded research projects, using computer models, are underway in Germany and the UK. Governments, and not business, should be the forum for research, particularly when it comes to solar radiation management which would have global impact.

“This giant leverage over the planet is a dangerous thing, and it shouldn’t be in private hands,” Keith said.

That’s not an idle worry. One of the most salient facts about geoengineering is that it will not cost much, especially when compared with the costs of reducing carbon emissions by switching away from fossil fuels, which have been estimated at about 1% of global GDP per year.

By contrast, geoengineering “is horrifically cheap to do. It now looks like you could alter the global climate for a couple of billion of dollars a year,” Keith said. (Less, in other words, than the cost of bailing out GM or running the National Park Service for a year.) “You can imagine scenarios in which small island nations got tired” of waiting for the major powers to act to curb global warming and took matters into their own hands. Or one where India or China, threatened by drought, acted unilaterally.

Perhaps not surprisingly, the talk about geoengineering has fed into conspiracy theories about how governments are already manipulating the climate, or worse. (Try googling chemtrails.) Keith has received hate mail, and Gates’ involvement has fueled suspicions that a cabal of the powerful is hatching secret plots.

Partly in response, Gates, Keith and Caldeira have decided to be much more transparent about how they are spending the research money. They’ve created a web page that explains where Gates’ money is being spent. They also make the point that they believe

that society should be spending many tens-of-billions of dollars per year developing and deploying affordable, scalable, near zero-carbon energy sources.

This is partly because no one claims that geoengineering will be able to solve all our climate-related problem. It has no effect, for example, on the problem of ocean acidification, which will get worse until greenhouse gas emissions are curbed. An unintended but predictable consequence of geoengineering is likely to be changing rainfall patterns. And, as always, we don’t know what we don’t know.

You can understand why this scares people. Probably, it should. Big ambitious technology projects works well until they don’t. Think the BP oil spill or the Challenger disaster.

So why go forward at all? Because, as I said, it’s been a bad year for the climate and worse year for climate policy.

Time to get ready for Plan B.