Why Focus on Agriculture and Forestry?
Land use, land use change and forestry (LULUCF) in the United States acts as a carbon sink, since vegetation and soils remove more carbon dioxide [CO2] from the atmosphere each year than they emit. In 2018, LULUCF removed enough CO2 to offset 12 percent of U.S. greenhouse gas (GHG) emissions. Separately from carbon removal in vegetation and soils, agriculture also produces emissions of potent GHGs such as nitrous oxide [N2O] from fertilizers and methane [CH4] from livestock, manure management and rice cultivation. The agricultural sector accounts for 10 percent of U.S. GHG emissions.[1]
What Makes the Agriculture and Forestry Sector Different in Terms of Reducing Carbon Emissions?
The agriculture and forestry sector presents significant opportunities for reducing emissions as well as removing carbon from the atmosphere. However, this sector also poses unique challenges for federal climate policy:
Diffuse sources and sinks: The U.S. contains about 750 million acres of forest land and over 1 billion acres of agricultural land, all of which contribute to carbon removal and GHG emissions. The majority of these lands are privately-held, meaning the government cannot exercise direct control over land use decisions. To significantly impact the trajectory of net GHG emissions in the sector, therefore, the government must persuade private landowners to change the way they manage millions of acres of land.
Interactions with natural processes: Unlike other sectors, forest and agricultural lands would continue to remove carbon and emit GHGs even in the absence of human activity: plants would continue to photosynthesize, soils would continue to accumulate carbon, and GHG emissions would continue from natural sources like wetlands and wildfires. Human activities like farming and forest management can augment or diminish these natural processes, but so can natural variations in temperature or rainfall. These interactions between natural and anthropogenic processes can make it difficult to draw a direct link from policies or land management changes to changes in the sector’s GHG balance.
Indirect measurement: Because the processes that remove carbon and emit GHGs in agriculture and forestry are complex and spread over large areas of land, GHG emissions and removals in the sector cannot be measured directly on a large scale with current technologies. GHG estimates in the sector instead rely on empirical equations that relate tree diameter and height to carbon stocks, models that simulate soil carbon sequestration and GHG emissions as a function of agricultural management practices, and statistical extrapolation that characterizes emissions and removals on a national level based on sample measurements. As a result of these indirect measurement techniques, GHG estimates from LULUCF are much more uncertain than those from other sectors.
[1] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions
