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It's easy to feel dispirited about climate change because the challenge of dealing with it seems so overwhelming. But Miguel Modestino is actually excited about the challenge. He's part of a large team hoping to make an artificial leaf — a device that would make motor fuel from sunlight and carbon dioxide rather than from fossil fuels.

Modestino grew up in Venezuela, a nation whose economy is based on oil and gas. But the brilliant high-school student made his way to the Massachusetts Institute of Technology, which offered him a fresh perspective.

"When I was a freshman, I was taking a course that was pretty much meant to guide you to what career to take," Modestino says, "and in this course we were discussing climate change and all the changes the planet is going through."

Modestino realized the skills he was acquiring as a chemical engineer could be useful in tackling the climate challenge. For graduate work, he left chilly Boston for the more comfortable climes of the University of California, Berkeley.

"When I arrived here, I realized there was a lot of clean energy research going on in Berkeley, and I decided to get engaged in an exciting project on solar fuels."

Right now we use solar panels to make electricity. But solar fuels would come from a device that uses sunlight to make something that could go in our gas tanks. Modestino is now part of a team of 120 scientists, engineers and technicians at the Joint Center for Artificial Photosynthesis.

Heinz Frei is the lead scientist of the part of the center that's affiliated with the Lawrence Berkeley National Laboratory. JCAP is a joint venture with Caltech. And at the moment, the Berkeley labs are spread out in an open room that feels like a squeaky clean warehouse.

Frei explains that the concept is to use sunlight as an energy source to take carbon dioxide from the air and turn it into fuel. That's exactly what green plants do.

"It's like an artificial leaf but spread over very large areas," he says. You would need a forest's worth of such leaves to make a meaningful amount of fuel.

At the moment, the engineers are still working on the basics: They're trying to capture energy from the sun to split water molecules into oxygen and hydrogen. Burn that hydrogen, and you can release a lot of energy.

Frei says it's not simply a matter of proving the concept of artificial photosynthesis — that was done a decade ago. The challenge now is to drive down the cost, using cheap materials and increasing the efficiency.

It turns out plants are actually not very efficient at making fuel. They convert just 0.3 percent of the sunlight they soak up to make sugars, which is their version of fuel. The goal of Frei's team at the Joint Center for Artificial Photosynthesis is to do it 10 times better, and to not produce hazardous hydrogen gas as the final product.

"The longer term goal is to make a liquid fuel so that it can be sent through pipes," Frei says.

If his team is successful, you might one day see huge blue solar collectors that, instead of being hooked up to the electrical grid, dripped a liquid that would be the starting material for a gasoline replacement.

At one workstation in the expansive lab, Modestino shows fellow graduate students John Stevens and Kenneth Lee how to use a piece of experimental gear that does just part of the work of an artificial leaf.

"So what we have right here is a system that can actually operate continuously producing hydrogen and oxygen," he says. Right now the system is plugged into the wall — hardly what you'd call solar powered. But for now, it's easier to break down the problem into bits, says Modestino, solving each component independently, before trying to piece together a working system.

Assuming they can make their artificial leaves out of cheap materials, Heinz Frei says the next challenge will be to scale it up.

"For a 1 percent efficient system — which is modest — you would need for the entire country an area that is equivalent to the interstate road systems," Frei says.

That's a lot of acreage. Frei acknowledges there could be significant political resistance to covering thousands of square miles of grassy hillsides and the like with endless arrays of solar collectors.

"Yes, but then the question becomes what's the alternative?" he asks. "If society refuses to accept this mode of making renewable fuel, the alternative is ... going on and using fossil fuel and fouling up the atmosphere with carbon dioxide to a level where the impacts on the living world around us become just intolerable."

Modestino, too, knows that building artificial leaves on a massive scale is a long shot, and can't be the sole solution. Even if the team is able to create a system big enough to fuel cars, trucks and airplanes, that won't be nearly enough to wean the world from fossil fuels. We still need to find clean ways to replace the coal and natural gas we burn to generate electricity. But you have to start somewhere, says Modestino who, like other young scientists in his field, sees the hunt for alternative sources of energy as an exciting frontier.

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