Is there still time to avoid runaway climate change? To a large degree, the answer depends on the feasibility of “negative emissions” — techniques or technologies that suck CO2 out of the air. In the latest report from the Intergovernmental Panel on Climate Change (IPCC), all scenarios for limiting warming to 1.5 degrees Celsius depend on negative emissions technologies or NETs. Most 2-degree scenarios also rely on negative emissions; many call for removing billions of tons of CO2 per year by mid-century.