Sunday, April 1, 2007

Ag Emissions and their Global Warming Potential, part 1

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.


SunWarm said...

Your website is very useful to me at the moment: I'm putting together a talk for Step it Up day on 4/14 about the effect of agribiz on global warming ( Thanks for all the links to charts and info!
The last piece of the puzzle for me is to talk about how conventional practices compare to sustainable practices, in terms of greenhouse gases,for example, constant tilling vs. cover cropping. If you have any sources, I'd love to get them:
keep it up!

Tim Crosby said...

Sorry I missed your posting until after Step it up day. I followed this effort in Seattle. Great idea, hope it went well wherever you are.

WA State University has a Climate Friendly Farming program ( that is investigating just this issue. There are other efforts going on; but where are you based? This can be a regional issue, or at least should take in to consideration the varying bioregional capapbilities for production.

Hope this helps.