Top 5 Geoengineering Schemes

For a long time, geoengineering sounded like a bad Hollywood action movie plot. In a rush to save the planet from global warming destruction, our sweaty-browed heroes take drastic measures. They launch giant mirrors into space! They create fake volcanoes! They build massive carbon-eating machines! Such plans used to be easy to ignore, and it didn't help that many started to emerge in the late 1970s.

In 2006, however, geoengineering began to shed its freak show reputation. Nobel Prize-winning chemist and ozone layer protector Paul Crutzen published a scientific editorial on the subject in the journal Climatic Change. He advocated exploring the use of sulfur aerosols in the atmosphere to cool the planet. Crutzen, dubbed "a scientist's scientist" by Time magazine, was difficult to dismiss. Now, even grizzled White House science adviser John Holdren is giving geoengineering credence. "We don't have the luxury of taking any approach off the table," he told the Associated Press.

Researchers at the University of East Anglia in the United Kingdom recently published the first comprehensive assessment of the most sweeping geoengineering schemes out there. "We just took the biggest number we could find in the literature," says co-author Naomi Vaughan, a postgraduate researcher in the university's School of Environmental Sciences. "You're looking at the maximum potential." For each proposed plan, the scientists calculated a value called "radiative forcing," which is a kind of index for climate modeling that shows the effect of manmade and natural factors on the planet. Since the industrial era began, we're largely responsible for turning up radiative forcing to 1.6 -- a value that could easily double in the future. The goal with geoengineering is to lower that number.

Although there are those who strictly define geoengineering as manmade patio umbrella equivalents for the Earth, the assessment included large-scale carbon sequestering. The scientists also assumed that any geoengineering effort would be used in conjunction with other kinds of mitigation. So even the most massive plans can't get us off the hook.

Here are the strongest contenders based on the university's methodology. Get ready for some big thinking. #5: Marine Stratiform Clouds