Carbon offsetting firms such as Carbon Footprint and CarbonNeutral, who invest in emissions reduction using money paid by individuals or companies to compensate for their own carbon emissions, include international tree planting schemes amongst the projects they invest in.
But the US Department of Energy-funded Free Air Carbon Enrichment (FACE) project found that plots of pine trees exposed daily for 10 years to 1.5 times the level of carbon dioxide in the current atmosphere, grew between 5 % and 40 % extra biomass, dependent on water and nutrient availability. Only those plots with the maximum nutrients and water grew enough biomass to compensate for the extra carbon dioxide.
The project also found that only parts of the tree such as the trunk store carbon dioxide for long periods of time – if the tree grows extra foliage in response to additional carbon dioxide, the stored emissions would rapidly return to the atmosphere.
Environmental groups such as Friends of the Earth are sceptical about carbon offsetting, which they believe allows people to buy their way out of the problem of greenhouse gas emissions instead of changing their lifestyle. Large tree planting carbon offsetting schemes in countries such as Ecuador infamously involve monocultural plantations of fast-growing species, and have been criticised for reducing biodiversity and displacing local people. This new study suggests that planting trees in areas likely to become increasingly drought-prone over the next 100 years such as the American southwest will not compensate for carbon emissions over the lifetime of the forest.
This article first appeared in the Ecologist August 2007