Climate change threatens an increasing list of worst-case scenarios: melting ice caps, rising sea levels, longer droughts, and more violent storms. Climate scientists have largely focused on reducing emissions to counter global warming, but a growing number view geoengineering as the Earth’s last, best line of defense. 

However, the concept is controversial and unproven, and it’s unclear if it could work. energyNOW! correspondent Josh Zepps explores geoengineering, from simple measures to complex atmospheric efforts, to find out if it can combat climate change. You can watch the full segment below:

Geoengineering, or climate engineering, is the study of manipulating the planet’s climate to counteract global warming’s effects. The potential solutions range from painting roofs white to absorb less heat, to launching trillions of transparent lenses a million miles into space to diffuse or divert sunlight before it reaches Earth. 

Regardless of the method, the impact could be more significant than emissions reductions alone. “Geoengineering is the one way that you can potentially actually cool off the entire planet relatively quickly,” said Samuel Thernstrom, policy advisor at the Clean Air Task Force. “It’s not clear that emissions can be reduced quickly enough to actually avoid fairly serious scenarios.”   

The geoengineering technology most often discussed is imitating volcanic eruptions. This method is based on the 1991 Mount Pinatubo eruption, which spewed a cloud of sulfate particles so large it cooled the Earth by about one degree for a few years. The effect, called solar radiation management, would scatter solar radiation across the atmosphere and back into space. 

A promising aspect of this approach is the ability to apply it to specific geographic locations through high-altitude balloons. “Maybe I don’t have to cover the whole globe with that volcanic aerosol,” said Michael MacCracken of the Climate Institute. “Maybe I can imitate a high latitude volcano and just have the sulfate at high latitudes over the Arctic Ocean.” 

One of the first real-world geoengineering experiments will test this concept. The Stratospheric Particle Injection for Climate Engineering project (SPICE) is a tethered balloon with a hose more than a dozen miles long to spray reflective particles into the upper atmosphere, and it could begin in Britain as soon as April 2012. 

Another way of managing solar radiation is to generate more ocean cloud cover. “If you could make these clouds denser and therefore brighter, they would reflect more sunlight,” said Thernstrom. “That is, at least theoretically, possible by spraying a very fine mist of salt water in the air, particles just the right size to help these clouds form.” Some estimates say 1,000-2,000 wind-powered, remote-controlled, seawater-spraying ships could offset global warming, at least for now. 

But the concept is not without critics, who say geoengineering could wreak havoc on our climate. “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,” said Pat Mooney, executive director of Canada’s ETC Group. 

His concerns helped the United Nations impose a geoengineering moratorium in 2010. To Mooney, the only way to combat global warming is emissions reductions. “Those are real, credible solutions, and its not too late,” he said. 

But for geoengineering advocates, having no backup plan at all is the worst option, given global emissions levels. “The whole problem is that we’re already interfering a great deal with the global climate,” said Thernstrom. “We are, in fact, engaged in a vast global geoengineering experiment right now – it’s just one that is entirely unintentional and uncontrolled.”