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LONDON (Reuters) - Greater use of woody fuels is vital to slash global carbon emissions but fast advances in crop yields will be needed to avoid driving up food prices, members of Germany's Potsdam Institute for Climate Impact Research found.
Biofuels are already widely used in the United States, Europe and Brazil to substitute for gasoline and diesel, but are made from crops including sugar, oilseeds and corn which has driven concerns they are stoking food prices.
That has led to calls for more advanced versions, made from woody biomass from trees and grasses like miscanthus, which can also be burned in furnaces to generate heat and power.
The comprehensive study of food, water, forest and energy impacts, published online on Thursday, found biomass could help the world meet ambitious carbon emissions targets but threatened natural forests and wildlife and could drive food prices higher.
The paper concluded that biomass made most sense in an approach that protected natural forests, piling even more pressure on farmland and so depending on yield advances to avoid deadly food price spikes in the future.
"Forest conservation combined with large-scale cultivation of dedicated bioenergy for climate change mitigation will generate conflicts with respect to food supply and water resource management," said the paper, published in the journal Environmental Research Letters.
"Integrated policies for energy production, land use and water management are therefore needed," said the authors.
Food yield increases of nearly 1 percent annually through 2095 were needed, it said, in a scenario that would see about a fifth of the world's energy come from biomass while conserving natural forests.
Such advances were possible but would add to the cost of bio-energy.
"Historical yield growth of about 1.3 percent (was achieved) annually from 1970 to 1995 averaged across all crops. Yield growth rates have declined in the most recent decade but yield growth potential is still considerable."
Bio-energy can help drive radical carbon cuts because it is one of the few understood ways to achieve negative carbon emissions.
That would entail an untested approach where carbon emissions from burning wood, for example, were trapped and buried underground, using carbon capture and storage (CCS) technology that is now under development to cut emissions from coal-fired power plants.
Thursday's study did not account for the fact that CCS is unproven.
Even without CCS, biomass is less carbon-emitting than fossil fuels, provided trees are replanted. That is driving interest in European countries which face tough carbon emissions and renewable energy targets for 2020.
Britain's biggest coal plant Drax last week won permission for biomass furnaces with a capacity of nearly 600 megawatts, drawing criticism from the wood panel industry which makes chipboard for furniture, and which feared rising competition would drive up wood prices.
Reporting by Gerard Wynn; Editing by Anthony Barker