A few sentences in a note from an obscure United Nations group has ignited a firestorm in the carbon removal world. At issue is a beguilingly simple question: What counts as a carbon offset?

The document — a draft to define a new global carbon market, released last month — elevated nature-based solutions like planting trees while downplaying the role of carbon dioxide removal (CDR) using machines or other forms of technology. Both natural and technological approaches can be effective ways to stave off the most catastrophic impacts of global warming. The demarcation might not sound like a big deal, but to the carbon removal industry, it’s existential.

Another U.N.-backed group, the Intergovernmental Panel on Climate Change (IPCC), has warned that the world will almost certainly need to remove billions of tons of carbon a year from the atmosphere by midcentury to limit warming to 1.5 degrees Celsius.