The scientists supported the use of waste materials from crops in bioenergy projects, but urged caution when assessing the emissions from ethanol made from corn

All bioenergy projects are not the same in terms of their beneficial impact on the emission of greenhouse gases compared to fossil fuels.

That was the warning from a group of 90 scientists yesterday, who urged leaders in Congress to pay close attention to greenhouse gas emissions from bioenergy sources when setting new climate and energy legislation.

While biomass is a much shorter-term store of carbon, leading to use of the term “carbon neutral” for bioenergy fuels, the scientists said the term was a “basic mistake”.

They warned that some forms of bioenergy can generate as much or more greenhouse gas emissions than equivalent fossil fuels.

Improper accounting for emissions from bioenergy projects could also lead to “large-scale destruction of forests”, the group claimed yesterday in a letter to US House Speaker Nancy Pelosi, US Majority Leader Harry Reid, and key Obama Administration officials.

In the letter, the scientists said: “Replacement of fossil fuels with bioenergy does not directly stop carbon dioxide emissions from tailpipes or smokestacks.

“Although fossil fuel emissions are reduced or eliminated, the combustion of biomass replaces fossil emissions with its own emissions (which may even be higher per unit of energy because of the lower energy to carbon ratio of biomass).”

Managed

The letter from the scientists did not slam all forms of bioenergy.

But, they pointed out that where land or plants are used for bioenergy, they must be managed properly to take up more carbon dioxide than they would have without their use in bioenergy projects.

The scientists also supported the use of vegetative residues, which would otherwise have been left to decompose and release carbon to the atmosphere rapidly, in bioenergy projects.

Projects in which fast-growing energy crops are grown on otherwise unproductive land was another way in which the absorption by plants could offset the emissions from their use in energy production according to the letter.

Perceptions

Dr William Schlesinger, a biogeochemist who is president of the Cary Institute of Ecosystem Studies and one of the signatories of the letter, said public perceptions that all biofuels and bioenergy was equally good for the environment was “not true”.

He said: “If our laws and regulations treat high-carbon-impact bioenergy sources, like today’s corn ethanol, as if they are low-carbon, we’re fooling ourselves and undercutting the purpose of those same laws and regulations.”

The scientists believe how the US treats emissions from bioenergy could have knock-on repercussions around the globe, influencing procedures in other countries and leading to “large-scale clearing of the world’s forests” as other nations seek to expand bioenergy usage and replace native woodland with energy crops.

The letter to Congress also suggested that failing to take proper account of carbon dioxide emissions from bioenergy projects could “seriously undermine” efforts to address climate change.

By assuming all bioenergy projects achieve a 100% reduction in greenhouse gas emissions, they claimed that “most” of the expected greenhouse gas reductions could be eliminated during the next decades.

If our laws treat high-carbon-impact bioenergy sources as if they are low-carbon, we’re fooling ourselves” - Dr William Schlesinger

Land use change

The calculation of carbon emissions in bioenergy can be immensely complicated, and issues such as land use change – the conversion of native areas of land to cultivate energy crops – can be difficult to measure while calculating the benefits of certain forms of bioenergy.

The letter from the 90 scientists yesterday came just a week after the National Corn Growers Association criticized California’s assumptions on the greenhouse gas emissions from corn ethanol.

The lobby group wants the California Air Resources Board (CARB) to forget about the issue of land use change entirely in its treatment of corn ethanol within the state’s Low Carbon Fuel Standard.

The Association cited a study from Purdue University stating that CARB was overestimating the greenhouse gas impact of land use changes in corn ethanol “by a factor of two”.

NCGA President Darrin Ihnen said last week: “By saddling corn-based ethanol with incorrect emissions, the California standard may actually increase its reliance on petroleum or foreign sources of ethanol, therefore worsening the environment and our national economy.”