How much land is available for reforestation?

2.3bn hectares of land have been deforested, releasing c25% of all anthropogenic emissions. This 19-page note reviews the technical literature, gathers detailed data and concludes 1.2bn hectares can be reforested. Consequently, there is room for 85Mbpd of oil and 400TCF of gas in a decarbonized energy system, while half of all ‘new energies’ technologies are overly expensive and may not be needed in the transition.

Scale matters for nature based solutions to climate change, as the ultimate running room for reforestation will determine how much oil and gas can be permitted in a fully decarbonized energy system; and how many high-cost technologies will be displaced from the abatement curve. These arguments are outline on pages 2-4.

Our models suggest a 15GTpa CO2 sink through reforestation, which is disaggregated on pages 5-6, including detailed data into the CO2 absorption rates of trees. Hence our models require 1.2bn hectares to be reforested.

How are the world’s 15bn hectares of land used? We present detailed data on pages 7-8. Criteria are suggested to prioritize the most effective lands for reforestation.

Degraded lands are the best opportunity for reforestation, as quantified and described on pages 9-10. Our work includes a case study of successful reforestation efforts.

Agriculture is now the largest land use on the planet, but changing habits, policies and technologies could liberate vast areas, as explored on pages 11-13.

Natural non-forests are feasible reforestation candidates, but they are the least preferable, as the goal is to ‘restore nature’, not convert one natural ecosystem into another (page 12).

Urban forests are also of high value, but too small to move the needle (page 13).

Precise bottom-up estimates of reforestation potential are made in the academic literature. Pages 16-18 cover the key studies in the field, and our own impressions on heated debates within the scientific community.

What if we are wrong? Nature is never certain, hence we consider this question on page 19, but we still believe our reforestation estimates are conservative.