To hit the Paris climate goals without geoengineering, the world has to do three broad – overambitious – things:
1. Global CO2 emissions from energy and industry have to fall in half each decade. That is, in the 2020s, the world cuts emissions in half. Then we do it again in the 2030s. Then we do it again in the 2040s. They dub this a “carbon law.” Lead author Johan Rockström told me they were thinking of an analogy to Moore’s law for transistors; we’ll see why.
2. Net emissions from land use — i.e., from agriculture and deforestation — have to fall steadily to zero by 2050. This would need to happen even as the world population grows and we’re feeding ever more people.
3. Technologies to suck carbon dioxide out of the atmosphere have to start scaling up massively, until we’re artificially pulling 5 gigatons of CO2 per year out of the atmosphere by 2050 — nearly double what all the world’s trees and soils already do. Link