July 11, 2008

Are Marginal Farmlands the Key to Sustainable Bioenergy?

There are many aspects that need to be considered when comparing the sustainability of different feedstock. We are all familiar with the feed vs. fuel debate. Then concern arose about land use change - deforesting to create land for growing biofuel feedstock. Ideally, the highest yielding, most sustainable energy crops would be grown on available land not already being used for any other purpose.

A recent study by scientists from Carnegie Institution and Stanford University that focus on the availability of "marginal farmlands" that are not forests, not being used to grow food crops, but are suitable for growing energy crops for conversion to bioenergy and biofuels.

Report Says Abandoned, Marginal Farmlands Key to Sustainable Bioenergy

Biofuels can be a sustainable part of the world's energy future, especially if bioenergy agriculture is developed on currently abandoned or degraded agricultural lands, report scientists from the Carnegie Institution and Stanford University. Using these lands for energy crops, instead of converting existing croplands or clearing new land, avoids competition with food production and preserves carbon-storing forests needed to mitigate climate change.

The report, The Global Potential of Bioenergy on Abandoned Agriculture Lands, asserts that sustainable bioenergy is likely to satisfy no more than 10 percent of the demand in the energy-intensive economies of North America, Europe, and Asia. But for some developing countries, notably in Sub-Saharan Africa, the potential exists to supply many times their current energy needs without compromising food supply or destroying forests.

Elliot Campbell, Robert Genova, and Christopher Field of the Carnegie Institution's Department of Global Ecology, with David Lobell of Stanford University, estimated the global extent of abandoned crop and pastureland and calculated their potential for sustainable bioenergy production from historical land-use data, satellite imaging, and ecosystem models. Agricultural areas that have been converted to urban areas or have reverted to forests were not included in the assessment.

The researchers estimate that globally up to 4.7 million square kilometers (approximately 1.8 million square miles) of abandoned lands could be available for growing energy crops. The potential yield of this land area, equivalent to nearly half the land area of the United States (including Alaska), depends on local soils and climate, as well as on the specific energy crops and cultivation methods in each region. Still, the researchers estimate that the worldwide harvestable dry biomass could amount to as much as 2.1 billion tons, with a total energy content of about 41 exajoules, nearly 7 billion barrels of oil, or about eight percent of the world's energy demand.

"At the national scale, the bioenergy potential is largest in the United States, Brazil, and Australia," says lead author Campbell. "These countries have the most extensive areas of abandoned crop and pasture lands. Eastern North America has the largest area of abandoned croplands, and the Midwest has the biggest expanse of abandoned pastureland."

The authors say that using these lands would generate about six percent of the nation's energy needs, though larger opportunities exist in other parts of the world. In some African countries, where grassland ecosystems are very productive and current fossil fuel demand is low, biomass could provide up to 37 times the energy currently used.
"Our study shows that there is clearly a potential for developing sustainable bioenergy, and we've been able to identify areas where biomass can be grown for energy, without endangering food security or making climate change worse," says Field, director of the Department of Global Ecology.

The results of the study were published in the June 25 online edition of Carnegie Institution for Science.

An abstract of the report :
Converting forest lands into bioenergy agriculture could accelerate climate change by emitting carbon stored in forests, while converting food agriculture lands into bioenergy agriculture could threaten food security. Both problems are potentially avoided by using abandoned agriculture lands for bioenergy agriculture. Here we show the global potential for bioenergy on abandoned agriculture lands to be less than 8% of current primary energy demand, based on historical land use data, satellite-derived land cover data, and global ecosystem modeling. The estimated global area of abandoned agriculture is 385−472 million hectares, or 66−110% of the areas reported in previous preliminary assessments. The area-weighted mean production of above-ground biomass is 4.3 tons ha−1 y−1, in contrast to estimates of up to 10 tons ha−1 y−1 in previous assessments. The energy content of potential biomass grown on 100% of abandoned agriculture lands is less than 10% of primary energy demand for most nations in North America, Europe, and Asia, but it represents many times the energy demand in some African nations where grasslands are relatively productive and current energy demand is low.

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