A carbon sink is anything that absorbs more carbon than it releases as carbon dioxide. European forests are currently a net carbon sink as they take in more carbon than they emit. In climate negotiations, this temporary reduction of carbon dioxide in the atmosphere is also known as negative emissions.
Forest carbon sinks are not an excuse to delay action in reducing fossil fuel emissions. This is because carbon absorbed by trees is dynamic. Forest carbon moves between the atmosphere (as carbon dioxide) and the tree (as carbon) in a continuous cycle, known as the forest carbon cycle.
Carbon stored in fossil fuel is static, remaining trapped outside the atmosphere for thousands of years. This means that forests can never cancel out or ‘offset’ emissions from fossil sources.
Using forest carbon sinks to justify carbon dioxide emissions from fossil sources will increase concentrations of carbon dioxide in the atmosphere, making it impossible to meet the global goal of keeping international temperature rises to well below 2°C.
Despite the clear difference between fossil and forest carbon, United Nations climate negotiators often suggest that planting trees or reducing deforestation is equivalent to reducing emissions from burning fossil fuels. Until this myth is finally busted, schemes to reduce emissions from deforestation and degradation (REDD), the Clean Development Mechanism or LULUCF have the potential to do more harm than good.
While it is quite possible to keep coal in the hole and oil in the soil, no government or company can ever ensure that carbon will remain in trees. Forest fires, insect outbreaks, decay, logging, land use changes and the decline of forest ecosystems as a result of climate change are all hard or impossible to control. This doesn’t mean we shouldn’t try to protect and restore forests, just that we need to do it at the same time as reducing fossil fuel emissions to zero.