An international team has found a critical error in the accounting method used to measure compliance with carbon limits and the flaw, which centers on the measurement of CO2 emissions from the use of bioenergy, could undermine greenhouse gas reduction goals if not addressed.
Current carbon accounting, used in the Kyoto Protocol and other climate legislation including the European Union's cap-and-trade law and the American Clean Energy and Security Act, does not factor CO2 released from tailpipes and smokestacks utilizing bioenergy nor does it count emissions resulting from land use changes when biomass is harvested or grown.
That means they consider bioenergy as carbon neutral regardless of the source of the biomass - which everyone except politicians knows is not true - and if penalties are instituted it means there economic incentives for large-scale land conversion to biomass. Which won't help global warming at all.
The authors in Science contend that across-the-board exemption of CO2 emissions from bioenergy is improper in greenhouse gas regulations if emissions due to land-use changes are also not included. "The potential of bioenergy to reduce greenhouse gas emissions inherently depends on the source of the biomass and its net land-use effects," the authors write.
Land-use emissions stemming from bioenergy use vary widely. Clearing established forests to burn wood or grow energy crops results in large releases of CO2 while converting unproductive land to support, for example, fast-growing grasses, may result in net carbon reduction. Under the current carbon accounting system, both scenarios are counted as a 100% reduction in energy emissions.
"When forests or other plants are harvested for bioenergy, the resulting carbon release must be counted either as land-use emissions or energy emissions," says Melillo. "If this is not done, the use of bioenergy will contribute to our greenhouse gas problem rather than help to solve it."
Melillo and his colleagues say the accounting flaw is fixable and call for a system that would track the actual flow of carbon and count all CO2 emissions, whether from fossil fuels or bioenergy. They further recommend that any crediting system for assessing bioenergy consider changes in carbon reserves; emissions of other damaging greenhouse gases other than CO2, such as nitrous oxide; as well as land-use emissions.
"Bioenergy has the potential to provide a substantial amount of energy and help nations meet greenhouse caps, but correct accounting must be in place to prevent unintended consequences of unsustainable bioenergy production," says Melillo.