Friday, October 23, 2009

Carbon consequences of the biofuels land use cascade

I've written here before about the land use cascade, the sequence of land transformations and land use changes that follow a change in one region.

A new Policy Forum in Science argues that ignoring the cascading carbon consequences of converting lands for biofuels will undercut global efforts to reduce greenhouse gas emissions.

The logic is not new. If croplands and pasture lands are converted to biofuel production, then some other forest or grassland must be cleared to produce the crops or providing the grazing area taken away by the biofuel production. It might happen in the neighbouring county. It might happen on another part of the planet. Either way, it will release soil carbon and plant carbon to the atmosphere (more immediately via burning or later via respiration and decomposition).

The authors argue that we need a new accounting system:

The accounting now used for assessing compliance with carbon limits in the Kyoto Protocol and in climate legislation contains a far-reaching but fixable flaw that will severely undermine greenhouse gas reduction goals (1). It does not count CO2 emitted from tailpipes and smokestacks when bioenergy is being used, but it also does not count changes in emissions from land use when biomass for energy is harvested or grown. This accounting erroneously treats all bioenergy as carbon neutral regardless of the source of the biomass, which may cause large differences in net emissions. For example, the clearing of long-established forests to burn wood or to grow energy crops is counted as a 100% reduction in energy emissions despite causing large releases of carbon.

If it is not fixed, this "accounting problem" has and will continue to cause poor national and international policy decisions.

The Kyoto Protocol caps the energy emissions of developed countries. But the protocol applies no limits to land use or any other emissions from developing countries, and special crediting rules for "forest management" allow developed countries to cancel out their own land-use emissions as well. Thus, maintaining the exemption for CO2 wrongly treats bioenergy from all biomass sources as carbon neutral, even if the source involves clearing forests for electricity in Europe or converting them to biodiesel crops in Asia.

This accounting error has carried over into the European Union's cap-and-trade law and the climate bill passed by the U.S. House of Representatives. Both regulate emissions from energy but not land use and then erroneously exempt CO2 emitted from bioenergy use.

How could it be fixed? The authors argue for a more full and fair accounting of emissions caused by biofuels or bioenergy.

The straightforward solution is to fix the accounting of bioenergy. That means tracing the actual flows of carbon and counting emissions from tailpipes and smokestacks whether from fossil energy or bioenergy. Instead of an assumption that all biomass offsets energy emissions, biomass should receive credit to the extent that its use results in additional carbon from enhanced plant growth or from the use of residues or biowastes. Under any crediting system, credits must reflect net changes in carbon stocks, emissions of non-CO2 greenhouse gases, and leakage emissions resulting from changes in land-use activities to replace crops or timber diverted to bioenergy.

This full accounting is necessary but will be difficult to implement given the uncertainty in soil carbon budgets and the complexity of the land use cascade.

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