Untangling the confusion around land carbon science and climate change mitigation policy

Depletion of ecosystem carbon stocks is a significant source of atmospheric CO 2 and reducing land-based emissions and maintaining land carbon stocks contributes to climate change mitigation. We summarize current understanding about human perturbation of the global carbon cycle, examine three scientific issues and consider implications for the interpretation of international climate change policy decisions, concluding that considering carbon storage on land as a means to 'offset' CO 2 emissions from burning fossil fuels (an idea with wide currency) is scientifically flawed. The capacity of terrestrial ecosystems to store carbon is finite and the current sequestration potential primarily reflects depletion due to past land use. Avoiding emissions from land carbon stocks and refilling depleted stocks reduces atmospheric CO 2 concentration, but the maximum amount of this reduction is equivalent to only a small fraction of potential fossil fuel emissions. 1990 levels. The target reduction was based on emissions from fossil fuels and industry, but removals by the land sector could be counted