PRINCETON, N.J.— When land shifts from producing corn to soybeans to kumquats, or from cropland to grazing land or bioenergy, or back to forest, does that help or hurt the world’s potential to mitigate climate change? A new paper in the December 13th edition of the journal Nature finds that typical methods used by policymakers and researchers to answer this question have not properly focused on the need to increase the efficiency of land to meet growing demands for both food and carbon storage. This limitation is particularly important because climate strategies require storing more carbon in forests and other native vegetation even as the world must produce 50 percent or more additional food per year.

“The fundamental problem is that policymakers and researchers have not truly confronted the fact that global land area is limited,” says lead author Tim Searchinger, Research Scholar at Princeton University’s Woodrow Wilson School and Senior Fellow at the World Resources Institute. “Using any hectare for one purpose comes at the cost of not using it for another, and these opportunity costs have not been truly counted.”

The paper finds that policymakers have failed to fully count the amount of carbon land could store in forests and other natural vegetation if not needed for food, and also failed to fully count the carbon needed to produce more food. Using a new method called the Carbon Benefits Index, the paper finds that many changes have different or much greater consequences than typically estimated, including:

  • Diets: The average European’s diet is responsible for as many greenhouse gases over roughly 30 years (around 9 gigatons per year), as are normally calculated for each European’s consumption of everything else combined, including energy. That is many times more than typical estimates of the climate consequences of food consumption. Shifting from beef, lamb and dairy to other foods would reduce these emissions by 70 percent.
  • Grazing: Improving grazing on a hectare of land in Brazil just from poor to medium level quality can increase the world’s capacity to store carbon as much as planting a hectare of forest in Europe or the United States. Many other analyses treat grazing land as expendable.
  • Biofuels and Electric Cars: Using ethanol or biodiesel contributes two to three times the greenhouse gas emissions of gasoline or diesel over more than 30 years. By contrast, vehicles using solar-sourced electricity, even using today’s inefficient batteries, produce only a few percent of the greenhouse gases of using gasoline or diesel.

The paper,“Assessing efficiency of changes in land use for mitigating climate change,” was co-authored by Stefan Wirsenius, of Chalmers University in Sweden, Tim Beringer of the Humboldt Institute at Berlin, and Patrice Dumas of CIRAD (Centre de coopération Internationale en Recherche Agronomique pour le Développement (CIRAD).

“Given the need both for more food and carbon storage, if land is good at producing corn and bad at producing forest, we want the land to produce corn but also vice versa,” says Searchinger. “The need is to make more efficient uses of land for all purposes.”

The basic question the paper addresses is which changes in the uses of land contribute to solving climate change by increasing the global capacity to meet both food needs and to store carbon.  This calculation can be challenging because land produces such different outputs, so the paper identifies ways to answer the question: ‘how much corn is worth how much kumquats and how much forest?’

The new method finds that the climate value of a kilogram or corn or vegetables can be based on the carbon lost from vegetation and soils to make them. Just as the economic value of such different products as a coat and a taxi ride can be compared based on the costs of producing them, so too can foods be compared to each other and to forests and bioenergy by the carbon costs of producing the foods. Policymakers, food companies and consumers can use this method to determine which changes help or harm efforts to solve climate change.

“It is important to increase both the efficiency of production on land and the efficiency of what we consume, such as what we eat, but it’s equally important that policymakers separate their efforts to influence each,” said Searchinger. “For example, beef is climate-inefficient and people can help the planet a lot by eating less, but so long as people demand beef, farmers can also help the planet by grazing beef more efficiently. Just discouraging a farmer from efficiently producing beef would hurt the climate because some less efficient farmer would likely produce the beef anyway.”

For more information contact Tim Searchinger at tsearchi@princeton.edu.