The Carbon Benefits Index
Based on “Assessing the Efficiency of Changes in Land Use for Mitigating Climate Change” Nature (2018)
Authored by: Timothy D. Searchinger (Princeton University & World Resources Institute, Stefan Wirsenius, (Chalmers University of Technology, ), Tim Beringer (Humboldt-Universität zu Berlin), Patrice Dumas, (Centre International de Recherche sur l’Environnement et le Développement, and Centre de coopération Internationale en Recherche Agronomique pour le Développement)
Which agricultural lands, if any, should we reforest? What are the net climate advantages or disadvantages of using more inputs to increase crop or pasture yields? What are the net consequences for mitigating the climate of shifting land to biofuel production? In general, which changes in how we use land or how we manage it are good for the climate and which are not and by how much? Relatedly, which changes in what we consume that affect land are good or bad for the climate, such as changes in diets?
These are critical questions because land use is a critical part of climate change challenges and solutions. The conversion of forests and other native habitats to agricultural use causes the net loss of nearly all the carbon otherwise stored in vegetation and much stored in soils. These conversions have contributed from one quarter to one third of the carbon people have added to the air, and conversion of forests and woodlands to agricultural use continue to contribute heavily to climate change. Virtually all climate strategies require eliminating these emissions quickly and many rely on large increases in forest by 2050.
Yet the world is now also on a path to require greater than 50% increases in crop production by 2050, and even larger increases in meat and milk that use pasture lands. And global land area is fixed. Simultaneously using global land to maintain or store more carbon while also producing more food therefore requires greater efficiency in the use of land.
A new paper in the December 13, 2018 issue of the journal Nature explains why existing methods for answering these questions have not truly evaluated the efficiency of changes in land use for climate change purposes, and there have not truly evaluated the effects on efficiency of changes in diets and other consumption. Existing methods tend to significantly underestimate the significance good and bad by not factoring in the opportunity cost of using land to produce food, or alternatively, the opportunity to store more carbon when land is not needed for food.
The paper develops a new quantitative method, called the Carbon Benefits Index, for doing these estimates on a hectare by hectare or land use parcel by parcel basis. These calculations can be done using a tool using Microsoft Excel.