To sink or burn? A discussion of the potential contributions of forests to greenhouse gas balances through storing carbon or providing biofuels

Abstract

Forests can affect net CO 2 emissions by increasing or decreasing the amount of stored carbon, or by supplying biofuels for power generation to substitute for fossil fuels. However, forests store the most carbon when they remain undisturbed and are allowed to grow to maturity, whereas using wood for bioenergy requires wood removal from forests, which reduces on-site carbon storage. Hence, it is difficult to manage a forest simultaneously for maximum carbon storage and supplying fuelwood. For developing optimal strategies for the use of vegetation sinks, it is necessary to consider the feedbacks via the inherent natural adjustments in the global carbon cycle. Increased atmospheric CO 2 currently provides a driving force for carbon uptake by natural carbon reservoirs, such as the world's oceans. When carbon is removed from the atmosphere and stored in biomass, it lowers the concentration gradient between the atmosphere and these other reservoirs. This reduces the subsequent inherent rate of CO 2 removal from the atmosphere. This means that transferring a quantity of CO 2 from the atmosphere to a biomass pool lowers the atmospheric concentration the most immediately after the initial removal, but subsequently, the atmospheric concentration trends back towards the values without biospheric removal. The optimal timing for the use of vegetation sinks therefore depends on a number of factors: the length of time over which forest growth can be maintained, whether biomass is used for energy generation and on the nature of the most detrimental aspects of climate-change impacts. Climate-change impacts related to the instantaneous effect of temperature are mitigated less by vegetation sinks than impacts that act via the cumulative effect of increased temperature. It also means that short-term carbon storage in temporary sinks is not generally beneficial in mitigating climate change.