There is a lot of buzz about carbon emissions and their impacts on global warming. But what other emissions are heating up the planet?
The UN's Intergovernmental Panel for Climate Change (IPCC) has become the trusted international body for much of this info. They track different gases in relation to their Global Warming Potential (GWP). The DOE's Energy Information Administration (EIA) has a very good definition about GWP and which gases are considered.
The main item I want to highlight right now is that the GWP ranks gases according to their carbon dioxide equivalent, the "radiative efficiency (heat-absorbing ability) of each gas relative to that of carbon dioxide (CO2 ).(1)". So, while CO2 while has a GWP rating of 1 (against itself), Methane (CH4) has a GWP of 23, and Nitrous Oxide (N2O) a GWP rating of 296. There are ten other gases that are tracked, but these three are the more commonly discussed .
The EPA's U.S. Greenhouse Gas Inventory Reports tracks the gas emissions and sinks (where GHG gases are taken in/reduced), and has a chapter devoted to agriculture impacts. It has a graph of GHG emissions from 2004 and states that "In 2004, the agricultural sector was responsible for emissions of 440.1 teragrams of CO2 equivalent (Tg CO2 Eq.), or 6 percent of total U.S. greenhouse gas emissions. " The report, though, only measures a few ag components: enteric fermentation in domestic livestock, livestock manure management, rice cultivation, agricultural soil management, and field burning of agricultural residues. There is a lot more that needs to be included to understand the full GHG impacts of our food system, and then what potential solutions exist for reducing our carbon equivalent footprint.
(1) US DOE EIA website page Global Warming Potentials, viewed April 1, 2007.