Forests as Carbon Sinks: How Forest Offset Projects Work
Guide · June 2026
Forests are the planet’s largest land carbon sink, which is why so many offset projects are built around them. But a forest credit is only as good as its permanence and additionality. Here is how forest carbon projects work — and where they fall short.
How forests store carbon
A forest is a giant carbon reservoir. Through photosynthesis, trees pull CO₂ from the air and bank it in trunks, roots and soil. Mature forests hold decades or centuries of accumulated carbon; intact tropical and boreal forests are among the largest carbon reservoirs on land.
That makes protecting existing forests one of the cheapest, fastest climate levers we have — and also one of the easiest to over-claim.
The main types of forest projects
Forest carbon projects fall into a few buckets. REDD+ pays to avoid deforestation that would otherwise happen. Afforestation and reforestation (ARR) plant new trees. Improved forest management (IFM) changes how a working forest is harvested. Each generates credits, and each carries different risks.
The catch: permanence, additionality, leakage
The hard questions never go away. Would the forest have been protected anyway (additionality)? Will it still stand in 30 years (permanence)? Did protecting one patch just push logging next door (leakage)? Reputable projects answer these with conservative crediting and long-term monitoring — the same scrutiny we apply in our funding approach.
Part of the bigger picture
This guide is part of our deeper look at carbon offsetting and what we fund instead.