A few weeks ago, David Keith, a physicist at the University of Calgary, got a write-up in The New York Times for pointing out that world governments are lavishing a fair bit of R&D money on fancy new solar panels or carbon sequestration for coal plants, but very little money—a paltry $3 million globally—on researching ways to suck out carbon that's already in the air. Now, Keith wasn't trying to dismiss research into advanced solar technology and the like—if anything, there's not enough of that R&D right now. But given that, according to one recent U.N. report, even the boldest schemes for decarbonizing and shrinking our emissions may not be enough to avoid a risky 2°C-or-more temperature rise, surely we ought to be exploring ways to take carbon out of the atmosphere, too, no?

So in that vein, over at Environment 360, David Biello takes a look at one of the more promising technologies—"artificial trees" that mimic the way plants vacuum CO2 out of the air and convert the carbon into a storable form. It sounds like a swell idea. And the technology's within grasp. But once you slip past the glossy concept, there's a whole parade of caveats ready and waiting:

Proponents of air-capture technology acknowledge it is far from a perfect solution and will not enable humankind to continue spewing CO2 into the atmosphere with impunity. First, although it has been successfully tested on a small scale, air capture is at least five years away from being tested on a larger scale and, after that, could take at least two decades before it could be widely deployed. Second, to set up enough artificial trees to make a dent in reducing the vast amounts of CO2 being produced by humanity would require massive production at enormous expense.

“The cost estimates for capturing CO2 from ambient air are gross underestimates,” says principal research engineer Howard Herzog at the Massachusetts Institute of Technology. “It’s actually still a question whether it will take more energy to capture CO2 than the CO2 associated with [fossil fuel] energy in the first place.”

Even if artificial trees do prove capable of pulling large amounts of CO2 from the air, scientists then face the problem of what to do with that carbon dioxide. Underground sequestration—one possible solution—is still in the experimental stages. And deploying such artificial trees on a mass scale will have significant environmental costs, including producing the electricity needed to run them, the large land area the air capture devices would occupy, and the manufacture and installation of devices using resins, plastics, and other substances that could release air pollutants.

Still, there's a strong case that this is worth looking into—not as a replacement for all the other well-trodden ideas for reducing our CO2 emissions, but at least as a supplement.