[ASSURAS] Welcome back to an environmental nightmare. Scientists who warn about global warming have a long list of worst-case scenarios -- Melting ice caps causing dangerous sea level rise. More frequent violent storms. Wilder wild fires and longer droughts. But other scientists say there could be ways to prevent such catastrophes, and they've got, quite literally, some "out of this world" ideas. "energyNOW"'s Josh Zepps takes us inside the fascinating and controversial world of geoengineering.

[ZEPPS] This is what the sky could look like every evening in what you might call a geoengineered world.

[SAMUEL THERNSTROM] Geoengineering is the one way that you can potentially actually cool off the entire planet relatively quickly, if necessary.

[ZEPPS] Samuel Thernstrom is a policy advisor at the Clean Air Task Force. Promoting research into how we might alter the climate is what he does.

[THERNSTROM] It's not clear that emissions can be reduced quickly enough to actually avoid fairly serious scenarios.

[ZEPPS] Geoengineering, also called climate engineering, is the study of how to manipulate the planet's climate to counteract the effects of global warming. It can be simple, like painting your roof white so it absorbs less heat. The folks at Lawrence Berkeley National Lab say that if cool roof colors were applied to all eligible roofs and pavements in temperate and tropical regions, the total cooling effect could be equivalent to getting 300 million cars off the road every year for 20 years. At the higher-tech end of the spectrum, some geoengineering plans are as complicated as launching trillions of 2-foot-wide transparent lenses a million miles into space to diffuse or divert sunlight before it gets to our overheated planet.

Somewhere between those extremes, the most widely discussed idea is the one that could send sunset lovers aquiver worldwide.

[MICHAEL MacCRACKEN, CLIMATE INSTITUTE] The approach that's discussed most is to try and imitate a volcano.

[ZEPPS] The volcano that gets the most credit for the idea is Mount Pinatubo in the Philippines, whose huge eruption in 1991 created a cloud of sulfate particles big enough to cool the Earth by about 1 degree Fahrenheit for a few years. Michael MacCracken is the chief scientist for climate change programs at the Climate Institute.

[MacCRACKEN] So that means it's scattering radiation but it's also scattering some back to space.

[ZEPPS] What he's talking about is a principle called "solar radiation management." One idea involves floating balloons high into the atmosphere to release light-reflecting sulfate particles.

[MacCRACKEN] Maybe I don't have to cover the whole globe with that volcanic aerosol. Maybe I can imitate a high latitude volcano and so just have the sulfate at high latitudes over the Arctic Ocean. We're going to lose the Arctic if we keep going on the path we are and don't do something. We're losing it!

[ZEPPS] What's the simplest and quickest way to save it?

[MacCRACKEN] Probably to reduce the amount of solar radiation going into the Arctic right now.

[ZEPPS] Another solar radiation management idea is to make more, and brighter, ocean clouds.

[THERNSTROM] If you could make these clouds denser, and therefore brighter, whiter, they would reflect more sunlight, and that is, at least theoretically, possible to do that by spraying a very fine mist of salt water in the air, particles just the right size to help these clouds form and help clouds that are forming become denser, whiter.

[ZEPPS] According to some estimates, 1,000 to 2,000 wind-powered, remote-controlled, seawater-spraying ships would be enough to offset global warming, for now.

Another space-based proposal involves giant umbrellas, or mirrors in orbit, shading the Earth's surface. Needless to say, not everyone is crazy about all this.

[PAT MOONEY, ETC GROUP] Who sets the mirrors? Who establishes the angle? If you have an extraordinarily hot day in New York or in Paris, do you adjust the mirrors to cool it down? And then what does that do to Africa when you make that adjustment? Who makes the decision?

[ZEPPS] Pat Mooney is one of the world's leading anti-geoengineering activists and the executive director of Canada's ETC Group, an international technology watchdog. He helped convince the United Nations to impose a moratorium on geoengineering in 2010. And his opinion of technologies that would blast sulfates into the stratosphere to cool Europe and North America?

[MOONEY] They could also knock the Asian monsoon off course, having it swing below South Asia, meaning that there'd be famine in South Asia and affect Africa in ways we're not even quite sure about.

[ZEPPS] Dr. Mooney says the only solution is emissions reductions.

[MOONEY] Need to be putting on the brakes on some of the things we're doing which are creating more greenhouse gases. Those are solutions, those are real, credible solutions, and it's not too late.

[MacCRACKEN] If we'd started in the 1970s when it first came up, you could have cut emissions and tried to do that, but we're just going higher and higher and higher, and cutting back is proving hard to do.

[ZEPPS] The objections to geoengineering are not just scientific. They're political.

[MOONEY] I don't have confidence that governments that have denied climate change for decades are actually going to be governments that will, in any way with integrity or intelligence, manage geoengineering. I don't trust them to control the planetary thermostat.

[ZEPPS] What would have to happen for you to be a convert?

[MOONEY] We'd have to have governments that we can trust. When's the last time --

[ZEPPS] As soon as pigs fly.

[MOONEY] Yeah.

[ZEPPS] But given that that's never going to happen, that means you're unwinnable.

[MOONEY] I'm unwinnable to the idea of geoengineering as a solution to climate change.

[ZEPPS] But for geoengineering advocates, the scariest thing is to have no backup plan at all.

[THERNSTROM] The whole problem is that we're already interfering a great deal with the global climate. We are, in fact, engaged in a vast global geoengineering experiment right now. It's just one that is entirely unintentional and uncontrolled.

[ZEPPS] So your opposition to geoengineering is really just an opposition to human hubris?

[MOONEY] There is a sense of naive confidence that somehow, just give us a chance and we'll do it right.

[ZEPPS] For his part, Michael MacCracken hopes we will rise to the challenge and prevent catastrophic climate change, by cutting emissions, through geoengineering, or with a combination of both.

[MacCRACKEN] I'm an engineer. I'm optimistic that we can do it. If you're a pessimist, it's too discouraging. I mean, we just have to keep working.

[ZEPPS] Josh Zepps, "energyNOW!"

[ASSURAS] One of the first real-world tests of geoengineering is supposed to take place in Britain within the next year. The Stratospheric Particle Injection for Climate Engineering project, or SPICE, is a tethered balloon with a hose more than a dozen miles long to spray reflective particles into the upper atmosphere to cool the planet. The SPICE group had planned to test the technology this year at a much lower altitude, about 3,000 feet, but its advisory panel recommended they hold off. The group says April 2012 is now the earliest the test can take place. Otherwise the hose may ice over.