The news seemed tailor-made to drive conspiracy theorists and members of the tinfoil hat club into a frenzy.

In July, the National Academy of Sciences confirmed that the CIA is helping to underwrite a yearlong study examining atmospheric geoengineering-deliberate, planetary-scale manipulation of the climate to counteract global warming. As reporters took jabs at the idea of "spooks" seeking to "control the weather," the National Academy of Sciences tried to brush away concerns. "We are not producing anything, building anything, or deploying anything. It's more of a state-of-the-science review," an academy spokesperson told me, noting that NASA and the National Oceanic and Atmospheric Administration (NOAA) are also helping to pay for the study. Still, the CIA's interest in geoengineering marks a turning point in the simmering debate about the controversial technology: More and more people are starting to take the once-laughable idea seriously.

Both supporters and skeptics of geoengineering schemes-which range from spewing sulfur dioxide particles into the stratosphere to dumping iron filings in the oceans-say planetary manipulation of the atmosphere is a Pandora's box that could unleash all kinds of environmental and geopolitical problems. While the CIA worries about other countries trying to weaponize the weather, environmentalists are anxious about the unforeseen ecological knock-on effects. Philosophers, meanwhile, caution that human ownership of the sky would place us in a new kind of existential bind.

Geoengineering has stood on the fringes of global-warming policy discussions for years. White House science adviser John Holdren is reported to have talked about it with President Barack Obama soon after he took office. In 2010, the House Committee on Science, Space and Technology held hearings on geoengineering; committee members stopped short of advocating for deployment and said research into the it should be "open and transparent," and spearheaded by the Department of Energy. Now the idea is taking on greater urgency. With the atmospheric concentration of carbon dioxide above 400 parts per million (the highest level in millions of years, according to NASA scientists) and global politics locked in a stalemate over emissions reductions, some climate scientists say we need to consider Plan B. Having unintentionally warmed up the planet, we may have no choice but to intentionally cool it back down.

Some of geoengineering's most prominent backers have mixed emotions about the enterprise, which only underscores how desperate our climate predicament has become. When it comes to hacking the sky, we're damned if we do, doomed if we don't.

"If I had to sum it up in a single word, I would say I'm ambivalent," says Ken Caldeira, an atmospheric scientist with the Carnegie Institution, a leading research organization. Caldeira's lab at Stanford University has conducted some of the most cutting-edge research into geoengineering, at first in the hopes of disproving the idea. After running experiments through his sophisticated climate models, Caldeira was dismayed to find that some techniques to manipulate the atmosphere got results. "Each attempt to poke holes showed that while [geoengineering] wasn't perfect, it seemed to work," he says. "Obviously, I would be much happier if we were not building any more smokestacks or tailpipes. But that's not what we're doing."

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Geoengineering schemes range from the whimsy of science fiction to the unnervingly plausible, with none free from concerns about unintended adverse consequences. University of Arizona astronomy professor J. Roger Angel's idea of launching a cloud of mirrors into space to reflect some of the sun's light away from Earth is probably a nonstarter. But several other geoengineering proposals are well within our technological capabilities. John Latham of the National Center for Atmospheric Research has suggested sending out a fleet of computer-directed boats to roam the oceans spraying seawater into the clouds to make them whiter; increasing the reflective power of the clouds by 3 percent, he predicts, could offset higher global temperatures. Another proposal involves dumping iron fillings into the oceans to spur blooms of carbon-dioxide-gobbling plankton that, after dying, would sink to the bottom of the ocean, taking the carbon with them. Several small-scale ocean fertilization experiments, however, have had mixed results.

The most widely discussed geoengineering technique goes by the somewhat Orwellian name of "solar radiation management." Scientists would inject a sulfur-dioxide aerosol into the stratosphere, and the extra particles would reflect more sunlight away from Earth in a planetary version of pulling down the shades, something nature has already tested: The 1991 eruption of Mount Pinatubo, a long-smoldering volcano in the Philippines, hurled an estimated 20 million tons of sulfur dioxide into the upper reaches of the atmosphere, where the ash turned into droplets of sulfuric acid that scattered the sun's light. The following year, global temperatures dropped by half a degree Celsius, and the summer melt of the Greenland ice sheet slowed.

Computer models have shown that humans could replicate the experience. "A continuous injection of a few tens of kilograms per second would be enough to offset a doubling of carbon dioxide," Caldeira told me when I started looking into geoengineering a few years ago. Powerful artillery could launch a sulfur-dioxide aerosol into the atmosphere. Another dispersal method would employ giant, high-altitude blimps equipped with hoses to carry sulfur from the planet's surface to the sky. A fleet of airplanes continuously circling the globe could also do the trick. Sulfur dioxide is plentiful and cheap (ironically, it's a byproduct of the coal combustion that's warming the planet), and as little as $1 billion a year could decrease sunlight by 1 percent.

Geoengineering skeptics cite a number of potential problems, ranging from the unpredictability of atmospheric manipulation to the chance that some rogue nation (or rogue billionaire) might start climate engineering without a global consensus.

For starters, no one is sure how ecosystems would react. What if blocking sunlight disrupted the South Asian monsoon cycle on which hundreds of millions of farmers depend? In a May New York Times op-ed, Australian academic and vocal geoengineering critic Clive Hamilton called out the threat of the unknown unknowns. "If there is one lesson we have learned from ecology, it is that the more closely we look at an ecosystem the more complex it becomes," wrote Hamilton, who is also the author of Earthmasters: The Dawn of the Age of Climate Engineering. "Now we are contemplating technologies that would attempt to manipulate the grandest and most complex ecosystem of them all-the planet itself."

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Geoengineering boosters say the solution may be to gradually deploy climate-control technology. "You could do 1 percent this year and 2 percent next year and then extend a plateau of non-warming," Caldeira says. "If things went awry, you could taper it back out and do it as gently as you can." But a steady ramp-up would be a nonstarter politically. One of the virtues of the sulfur-dioxide aerosol scheme is that it's speedy, unlike emissions reductions, which will take decades to have a noticeable effect. "The most politically plausible scenario is that nothing is done until there's a real crisis and an untested system is deployed," Caldeira says.

Yet the very prospect of some last-minute, civilization-saving contraption could make us more cavalier about wrecking the climate. "It might be tempting to do [geoengineering] rather than the harder work of [greenhouse gas] mitigation," says Alan Robock, a Rutgers environmental sciences professor who received a National Science Foundation grant to plumb the political and ethical implications of geoengineering. "If you tried to do it without mitigation, it would be a disaster."

Even geoengineering backers acknowledge this problem. "It's fast, cheap-and imperfect. Those are the defining characteristics," says Harvard applied physics and public policy professor David Keith, author of the forthcoming book A Case for GeoEngineering. "People with ski helmets go faster. People drive closer to bicyclists who have helmets on than bicyclists who aren't wearing helmets. It's called risk compensation. It's ubiquitous, and it's rational."

But according to Robock, at least one study has shown that, when told about the prospect of geoengineering, people become more concerned about global warming. If leading scientists are thinking about tinkering with the atmosphere, things must be bad, some people conclude. There could be an interesting political dimension at work as well. A study published last year by Yale law and psychology professor Dan Kahan found that self-described conservatives were more likely to accept evidence of man-made climate change if they were told about the possibility of geoengineering. Notably, prominent conservative think tanks like the American Enterprise Institute and the Hudson Institute have expressed interest in geoengineering.

There are also serious geopolitical complications involved with geoengineering, probably one of the main factors fueling the CIA's interest in the technology. The problem has to do with global governance. Who would decide when it's time to hit the launch button, and who would control the global thermostat? What if Brazil wants it cooler, but Russia wants it warmer?

"If we are talking about sulfate aerosol spraying, once we start, we will not be able to stop," Clive Hamilton wrote to me in an e-mail. "So who will control the world's weather for the next thousand years? The Central Committee of the Chinese Communist Party? The Pentagon? A U.N. expert group? The Security Council? In the end, there will be a power struggle over who will regulate the climate. If I were a poor farmer in Bangladesh, I would not be confident that my interests would be taken seriously."

In the absence of global consensus, some country (or a small group of countries) might decide to do geoengineering on its own. That could lead to conflict, even war. The potential of for unilateral geoengineering seems to be driving the CIA's interest in the technology. Both David Keith and Alan Robock say they have been interviewed by a CIA contractor investigating the potential of another country weaponizing geoengineering. (The CIA did not respond to phone calls asking for comment.)

Equally worrisome is the prospect of some well-intentioned but overreaching billionaire deciding to rescue the world solo-a James Bond-like situation that some have cheekily dubbed a "Greenfinger" scenario. "What if Richard Branson wanted to save the planet?" Robock says. "He's got a lot of airplanes."

This isn't an academic concern. In July 2012, California businessman Russ George, founder of the for-profit geoengineering outfit Planktos, dumped 100 tons of iron sulfate into the Pacific Ocean off the coast of British Columbia. The experiment seemed to work: Satellite images showed a plankton bloom as large as 10,000 square kilometers. But the United Nations' International Maritime Organization expressed "grave concern" about the test, which violated a 2010 the UN Framework Convention on Biological Diversity agreement that put in place a (largely symbolic) moratorium on geoengineering research. (Interestingly, Bill Gates is one of the largest funders of Ken Caldeira's geoengineering research. Caldeira says the support comes from Gates' private pockets, not his philanthropic organizations.)

Once we start messing with the sky, there will be no going back. If we were to suddenly lose the technological or financial ability or political will to keep altering the sunlight, global temperatures would spike rapidly, putting us in even greater danger. We will always be fearful of letting our grip slip from the lever that keeps the planet in a semblance of balance. It would be existential anxiety unlike any we've felt since the nuclear-weapons hair trigger of the Cold War.

Other psychological ramifications shouldn't be underestimated. More than 20 years ago in his prescient, The End of Nature, Bill McKibben warned of "the imposition of our artificial world in the place of a broken one." A sulfur-dioxide aerosol could, for instance, bleach the daytime sky, fading its blueness, and at the same time turn sunsets into Martian-like displays of super-saturated reds and oranges. Who knows how this would affect us. Perhaps we'd feel nothing. But maybe it would be maddening-an outcome suggested by the expressionist painting "The Scream," inspired by the otherworldly sunsets that followed the 1883 eruption of the Indonesian volcano Krakatoa.

For at least the last 25 years, we've been dumping carbon and methane into the air knowing full well the risks of doing so. When it comes to planetary-scale manipulation, we crossed the line a long time ago. Still, something like solar radiation management would mark an unprecedented leap in humanity's ownership of Earth. Geoengineering would turn us into a kind of bubble species, all of us living inside a massive armature. If that comes to pass, the world might no longer give us the comfort of home. Instead, the Earth might come to seem like a foreign country, a vague and threatening enemy. A prospect, it appears, that makes even the CIA nervous.