Exposé of false carbon accounting for biofuels

Cover of a brochure on a 'biorefinery' project in Sweden

False carbon accounting for biofuels that ignores emissions in landuse change is a major driver of global natural habitat destruction, incurring carbon debts that take decades and centuries to repay; at the same time, the emissions of nitrous oxide from fertilizer use has been greatly underestimated, says a damning new briefing from the Institute of Science in Society (I-SIS), Britain.

A team of thirteen scientists led by Timothy Searchinger at Princeton University, New Jersey, in the United States, pointed to a “far-reaching” flaw in carbon emissions accounting for biofuels in the Kyoto Protocol and in climate legislation. It leaves out CO2 emission from tailpipes and smokestacks when bioenergy is used, and most seriously of all, it does not count emissions from land use change when biomass is grown and harvested, says the I-SIS briefing.

“The team maintained that bioenergy reduces greenhouse emission only if the growth and harvesting of the biomass for energy captures carbon above and beyond what would be sequestered anyway, and offsets the emissions from energy use. This additional carbon may result from land management changes that increase plant uptake or from the use of biomass that would otherwise decompose rapidly.”

Graph from World Energy Outlook 2010 titled 'Ranges of well-to-wheels emission savings relative to gasoline and diesel'.

“The worst case is when the bioenergy crops displace forest or grassland, the carbon released from soils and vegetation, plus lost future sequestration generate huge carbon debts against the carbon the crops absorb, which could take decades and hundreds of years to repay.”

The work of Searchinger, referred to by I-SIS, has been mentioned in connection with this false accounting as long as a year ago. For instance, the Industrial Biotechnology and Climate Change blog had noted in 2009 November:

The Science Insider blog last week hosted an interesting debate between Tim Searchinger, Princeton visiting scholar, and John Sheehan, of the Institute on the Environment at the University of Minnesota, regarding the recent policy proposal in the pages of Science by Searchinger et al. to ‘fix’ the carbon accounting of biomass for bioenergy and biofuels in U.S. legislation and the successor to the Kyoto protocol, by giving credit only to biomass that can be managed in such a way as to sequester additional atmospheric carbon in the soil. As Searchinger puts it in the recent debate, “bioenergy only reduces greenhouse gases if it results from additional plant growth or in some other way uses carbon that would not otherwise be stored.”

Cover of the World Energy Outlook 2010 report, International Energy Agency

Also pertinent is a short section on biofuels and emissions in the World Energy Outlook 2010, which has recently been released by the International Energy Agency. “Biofuels are derived from renewable biomass feedstocks, but biofuels are not emission-free on a life-cycle basis,” says WEO2010. There is keen debate about the level of emissions savings that can be attributed to the use of biofuels and, more generally, to biomass. Greenhouse-gas emissions can occur at any step of the biofuels supply chain. Besides emissions at the combustion stage, greenhouse-gas emissions arise from fossil-energy use in the construction and operation of the biofuels conversion plant. In addition, the cultivation of biomass requires fertilisers, the use of machinery and irrigation, all of which also generate emissions.”

The short section is part of Chapter 12 – titled ‘Outlook for Renewable Energy’ – of the massive tome, and the section on Biofuels emissions is found in pages 372-374. As the WEO must perforce sound upbeat about all forms and sources of energy, it ventures, “If appropriate feedstocks and process conditions are chosen, biofuels can offer significant net greenhouse-gas emissions savings over conventional fossil fuels”. That’s a big “if” there.

“This is particularly the case with sugar cane ethanol, as much less energy is required to convert the biomass to ethanol.” In a laboratory perhaps, but as there are as many ways of converting sugarcane as there are types of cane, it would be difficult to say, wouldn’t it?  “But variations are large and calculating average emissions savings is complex.” So they are, so it is.

After such kerfuffle, the WEO2010 does get down to brass tacks: “Using land for biofuels production that was previously covered with carbon-rich forest or where the soil carbon content is high can release considerable amounts of greenhouse gases, and even lead to a ‘carbon debt’. In the worst cases, this debt could take hundreds or even thousands of years to recover via the savings in emissions by substituting biofuels for fossil fuels.”

And there you have it, in black and white, from the venerable International Energy Agency itself.