A 2005 study suggests that rising atmospheric CO2 will ultimately lead to reduced carbon sequestration through trees’ roots in forest soil. Therefore, as CO2 levels increase in the atmosphere, forests will not be able to perform their role as carbon sinks as well as they do under lower concentrations – in turn, increasing the level of CO2 that will stay in the atmosphere and exacerbate global warming.
- Heath, James et al. “Rising Atmospheric CO2 Reduces Sequestration of Root-Derived Soil Carbon.” Science 309(5741): 1711-1713. 9 September 2005 at www.sciencemag.org
The authors conclude that while increased levels of atmospheric CO2 leads to increased tree growth, associated increases in microbial respiration lead to a decreasing quantity of CO2 being sequestered through the trees’ roots into the forest soil. Observed reductions were approximately 40%. While the study examined only a small sample, the authors believe the process would hold at large scale, and suggests that annual carbon sequestration through sinks may be significantly reduced in the future as atmospheric carbon dioxide levels rise.
Implications: The study’s findings imply that projections of carbon sequestration are likely optimistic. If forests are not able to sequester carbon at the rates anticipated, global warming is likely to proceed at a much more rapid rate than anticipated. Furthermore, the process seems to create a positive feedback loop: the higher the atmospheric levels of CO2, the less soils absorb – and therefore, the more rapidly atmospheric levels rise. Thus, not only may efforts to control global GHG concentrations through forest carbon sequestration be limited, but we may need to revise upward our expectations of the rate of global climate change.
