Nations worldwide have agreed to limit carbon dioxide emissions in hopes of preventing global warming from surpassing 2 degrees Celsius by 2100. But countries will not manage to meet their goals at the rate they’re going. To limit warming, nations will also likely need to physically remove carbon from the atmosphere. And to do that, they will have to deploy “negative emissions technology”—techniques that scrub CO2 out of the air.

Can these techniques, such as covering farmland with crushed silica, work? Researchers acknowledge that they have yet to invent a truly cost-effective, scalable and sustainable technology that can remove the needed amount of carbon dioxide, but they maintain that the world should continue to look into the options. “Negative emissions technologies are coming into play because the math [on climate change] is so intense and unforgiving,” Katharine Mach, a senior research scientist at Stanford University. Last week at the American Geophysical Union conference in San Francisco, researchers presented several intriguing negative emissions strategies, as well as the drawbacks.

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