Some scientists are taking a more radical approach to cooling the earth's climate, like dumping iron dust into the ocean, hoping to grow algae blooms that suck up carbon. Or putting a giant lens between the Earth and the sun to reflect some of the sun's rays away from Earth.

It's all part of a controversial field known as geoengineering, and science writer Eli Kintisch spent three years following the men and women who believe it can work for his new book, Hack the Planet: Science's Best Hope -- or Worst Nightmare -- for Averting Climate Catastrophe.

Kintisch tells NPR's Guy Raz that many scientists see geoengineering as a sort of insurance policy. "We might face emergencies in the future which driving a Prius or putting up a windmill or putting up a solar panel will not answer," he says.

So, those scientists argue, we have to have backup plans.

One of those backup plans is known as the "Pinatubo Option." The name refers to a 1991 volcanic eruption that spewed more than 10 million tons of sulfur dioxide into the atmosphere. That blocked a small percentage of the sun's rays and cooled the planet by 1 degree Fahrenheit. One scientist imagines mimicking this volcanic cooling effect by spraying more sulfur dioxide at high altitudes.

"But cooling the planet with something like the Pinatubo Option doesn't address the underlying issues," Kintisch says. It also could have serious side effects.

"You might actually damage the ability of solar panels to take in energy, because you are blocking direct sunlight that those panels need to create energy," Kintisch warns. "So by doing geoengineering and removing direct sunlight from the planet's system, you're actually undermining the alternative energy we need to get off our fossil fuel addiction."

Another scientist is taking a different approach to geoengineering. Instead of looking to the sky for solutions, he's looking to the ocean. Victor Smetacek, a German oceanographer, is trying to cool the planet by growing carbon-absorbing gardens in parts of the ocean with little life.

In 2009, Smetacek and a team of Indian and German scientists added 6 tons of iron into a section of the Southern Ocean, which rings Antarctica, to see if they could get a massive bloom of algae to flourish. Algae growing in the ocean cools the planet by sucking in carbon dioxide. The team did get algae to grow, but it was the wrong kind of algae.

The 10-week experiment, called project LOHAFEX, is the world's largest geoengineering project to date, and, like many other geoengineering attempts, was controversial. Greenpeace and other environmental organizations demanded that LOHAFEX be stopped from the start, saying that pouring iron into the ocean amounted to pollution and violated international agreements. Some scientists feared the unintended side effects of the project.

"In the case of fertilizing the ocean," Kintisch explains, "you might create areas that are deprived of oxygen. You might alter ecosystems in ways you don't understand. You might actually create organisms in your algae patch that put up greenhouse gasses more potent than the carbon dioxide, like methane."

Despite the potential drawbacks of geoengineering, major science organizations such as the American Geophysical Union, the Royal Society in London, and the National Academy of Sciences have all called for more geoengineering research.

"It's a bad idea whose time has come," Kintisch says.

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