New index helps quantify impact of land use, diets on climate change
A study published in Nature suggests that governments and researchers have been underestimating the significance of land and diets to reduce climate change, and proposes a new quantitative method, called the Carbon Benefits Index, to estimate more accurately the impact of land use and diets.
A study published in Nature suggests that governments and researchers have been underestimating the significance of land and diets to reduce climate change, and proposes a new quantitative method, called the Carbon Benefits Index, to estimate more accurately the impact of land use and diets. “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% or more additional food per year,” explained study author Timothy Searchinger, research scholar at Princeton University and senior fellow at the World Resources Institute.
According to the authors, 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. But measuring the efficiency of land-use changes from the perspective of greenhouse gas emissions is challenging, particularly when land outputs change, for example, from one food to another or from food to carbon storage in forests.
The researchers developed the Carbon Benefits Index to measure how changes in the output types, output quantities, and production processes of a hectare of land contribute to the global capacity to store carbon and to reduce total greenhouse gas emissions. This index does not evaluate biodiversity or other ecosystem values, which must be analyzed separately. The researchers have applied the index to a range of land-use and consumption choices relevant to climate policy, such as reforesting pastures, biofuel production, and diet changes. They found that 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%.
In addition, they found that 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. Finally, they determined that using ethanol or biodiesel contributes two to three times the greenhouse gas emissions of gasoline or diesel over more than 30 years.