In a report published earlier this month in Science, Marine Biological Laboratory senior scientist Jerry M. Melillo and research associate David W. Kicklighter found the costs of producing biofuels may outweigh the benefits of burning them.

Due to a rising demand for corn-based ethanol, cropland in the United States is slowly being converted from food to biofuel production, Dr. Melillo said, mirroring a global trend.

The scientists’ model, which looked at economic and biogeochemistry data, predicted that the land devoted to biofuels will become greater than the total area currently devoted to growing food by the end of this century.

The displacement of food crops and forests for growing biofuel products will release up to twice as much as the carbon dioxide (CO2) emitted from the same land, they found.

“Large greenhouse gas emissions from these indirect land-use changes are unintended consequences of a global biofuels program, consequences that add to the climate-change problem rather than helping to solve it,” said Dr. Melillo.

Oil for food

Increasing biofuel consumption in the United States may also lead to land use changes in other parts of the world. Dr. Melillo pointed out that as the United States grows more corn, it is growing less soybeans, which are in high demand from China. As a result, China is buying more soybeans from Brazil, a country that is rapidly destroying its rainforests to convert to agricultural production.

“Our ethanol production is having knock-off consequences on land use in Brazil. There are several degrees of separation but everything is connected,” Dr. Melillo said.

Growing more biofuel crops could also mean that fertilizer use will increase, resulting in greater nitrous oxide (N²O) emissions. Dr. Melillo said this potent greenhouse gas could become more important than carbon dioxide as a driver of climate change by the end of the century.

“When you cut down [trees or crops], you release carbon. Burning wood in remote tropics, or allowing it to decay, that’s a big pulse of carbon. And once you clear the land, the next thing is to fertilize,” Dr. Melillo said.

The N²O threat

Unwillingness to use fertile cropland to grow biofuel plants can mean that less productive land—and more fertilizer—is used, Dr. Melillo said. By 2100, the scientists estimated that more than half of the total N²O emissions will come from fertilizer, surpassing CO² as the leading cause of global warming.

For this reason, Dr. Melillo said that N2O emissions are what he is worried about over the long term.

“Fertilization is probably going to go on for a long time. Whereas, the large carbon losses occur around the time of conversion of natural lands,” he said.

Current climate policy is aimed at reducing CO2 emissions to 350 parts per million, a target that some countries are trying to achieve by increasing their dependence on biofuels. So far, Dr. Melillo said, greenhouse gas emissions from biofuel-related land use change are not included in any country’s carbon credit accounting.

Furthermore, the spin-off effects of such policies, Dr. Melillo said, could mean that land prices will increase, leading to higher prices for food and wood products.

Because most of the ethanol used in Massachusetts is not produced in the state, he said that the ecological consequences in the US will mostly be felt in the Midwest, where farms and refineries dedicated to ethanol production have sprouted up.

“Corn is a nitrogen-demanding crop. It does not use fertilizer efficiently, so it runs off into the groundwater, down the Mississippi, and to the Gulf Coast,” Dr. Melillo said.

“I have a feeling there will be work in the agricultural community to maximize the efficiency using of nitrogen by breeding crops,” he said.

While Dr. Melillo said he is not planning to attend the United Nations climate change conference in Copenhagen next month, he will present his research on biofuel issues to officials in the European Union next week. He will be pushing for a global greenhouse gas emissions policy that protects forests and encourages best practices for nitrogen fertilizer that will reduce emissions associated with biofuels production.