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It’s no secret that the world’s expanding population and corresponding resource needs present a host of complex environmental management challenges. More people means more food and more energy use, which in turns means increased greenhouse gas emissions, more pressure on forests, water supplies, and the ecosystems which account for much of the world’s biodiversity. And as more countries develop plans for expanding and exploiting domestic sources of bioenergy, the global carbon management picture becomes even more complicated.
“The world’s forest, grassland and agricultural ecosystems not only help to fulfill human society’s needs for food, energy and materials but also harbour a wealth of biodiversity of intrinsic and utilitarian value,” according to Jan-Erik Petersen of the European Environment Agency. While not arguing against the pursuit of policies directed toward harvesting more of the bioenergy potential stored in forests and fields around the world, Petersen urges caution, pointing out that stakeholders must seek to achieve a delicate balance between the competing demands on the world’s usable land. “The likely future impacts from climate change and the increase in food demand over the coming decades requires careful reflection about which human needs the available agricultural land area should primarily be used for without endangering its future productivity and ecological functions,” he says.
When examining the potential impact of energy production from biomass, Petersen says it’s important to take into account both the greenhouse gas balance over the entire energy production cycle, as well as the associated pressures on natural resources and biodiversity. “The effects of direct and indirect land use change associated with the production of biomass for energy are critical for both issues,” he says. Petersen argues that rising food prices and the projected increase in global demand for food in the decades ahead mean that one can no longer assume energy cropping won’t generate land use changes. Consequently, previously assumed benefits for the greenhouse gas balance associated with different biofuel options may no longer be valid.
The question which needs to be answered, therefore, is how large the various direct and indirect land use effects are likely to be, and how they can be measured. Fortunately, work in tackling this question is already underway, as evidence by two recent studies which represent important steps in carbon loss modeling related to the conversion of forests, grasslands and idle land into energy crops. One project, led by Fargione, shows that greenhouse gas balance improvements associated with South American sugar cane start to disappear when the crop is grown in land converted from forests. The second, led by Searchinger, uses an agroeconomic model (the CARD system) to demonstrate the importance of global displacement effects related to ethanol produced from corn and switch grass in the United States.
The study_ shows that, under certain assumptions, carbon emissions from converting forests or grasslands to energy crops may actually lead to higher green house gas emissions compared to fossil fuels, when viewed over a 50 year time horizon. “A crucial, question with regard to the overall green house gas balances for different bioenergy pathways is whether they are likely to engender indirect land use change from carbon rich land cover types to arable energy crops,” says Petersen. “In this context, the effects of individual national biofuel or energy targets cannot be looked at in isolation but need to be considered together,” he adds.
While Petersen points out that greenhouse gas emissions associated with changes in land use are relatively easy to model, investigating the impact of using crops for bioenergy on biodiversity and natural resources requires more comprehensive on-the-ground monitoring and modeling. Thus policymakers and industry face a difficult challenge in navigating the additional carbon cycle challenges presented by the opportunity of bioenergy crops. But Petersen argues there is reason for cautious optimism.
An appropriate mix of policies to support bioenergy production, as well as advances in technology will likely lead to an expansion in the number of available feedstocks, as well as improve the greenhouse gas balance and energy efficiency for second generation bioenergy. The key, however, will be to introduce policies which reduce land use-related greenhouse gas emissions associated with harvesting energy from biomass. “Increasing global food demand and the necessary public and economic support for maintaining and improving carbon sinks will likely limit the land available for biomass production, at least for arable energy crops,” says Petersen.
As a result, he argues, policymakers must bear in mind that current bioenergy targets may ultimately increase rather then reduce greenhouse gas emissions, depending on the associated level of land use change. In addition, it’s important to continue the search for feedstocks which minimize competition with food markets and which maximize emissions reduction. New models, he says, “need to analyse the interaction between food, feed, biomass, and material markets” as well as the environmental impact associated with biomass production in different parts of the world.
Another important consideration is examining the effects on possible markets for carbon, which Petersen sees as vital for judging the comparative societal benefits between using land for food, biomass, or as carbon sinks.
“We need to consider how best to combine the carbon sink functions of agriculture and forest land with their productive functions, and how to provide economic compensation to land owners/managers that forego economic benefits from land use conversion,” says Petersen.
While increasing demand for bioenergy complicates efforts to achieve greenhouse gas emissions targets, the challenge is by no means insurmountable, according to Jan-Erik Petersen of the European Environment Agency.