BioCycle May 2010, Vol. 51, No. 5, p. 52
Sally Brown

I think it is fair to say that, as a culture, we are generally obsessed with this whole idea of mortality. There is that song that I would be perfectly happy never hearing again, “Dust in the Wind,” which emphasizes our transient time here on earth. Then there is the song that I could hear several times a day, especially when Louis and Ella sing it, with the lyrics “Methusula lived 900 years, Methusala lived 900 years, but who calls that living when no gal will give in to some man whose 900 years.” In my mind that is a fine reason to throw in the towel at a much younger age, soon after the gals stop giving in and while you can still remember what they looked like.
Unfortunately greenhouse gas accounting currently errs much more on the Methusula side of things. Everything is calculated using a 100-year time frame. Is the Intergovernmental Panel on Climate Change (IPCC) – the leading body for the assessment of climate change, established in 1988 by the United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO) – also obsessed with mortality and if so, is this such a bad thing?
There is one potential explanation for the 100-year time frame that makes sense to me and two unintended effects of this that don’t make so much sense. The goal of the IPCC and the Kyoto protocol is to bring about significant and permanent changes in atmospheric CO2 concentrations. This makes sense. Say you want to get credits for doing the right thing and plant a whole bunch of trees to get reforestation credits. Say that 15 years into it you get an offer from a real estate developer to turn all of those trees into an open air shopping plaza. So much for the reforestation credits.
The 100-year time frame requirement is a way to assure that the changes made in emissions are more permanent than we are. This adds credibility to the credits and makes it clear that both the Kyoto Protocol and the IPCC mean business. It is one of the ways that the snake oil is taken out of the carbon crediting process. This is the good part of the 100-year time frame.

OK FOR SCIENCE, BAD FOR POLICY
One of the bad parts of the 100-year time frame relates to methane gas. Methane only lasts in the atmosphere for 10 to 12 years. It is also a highly potent gas, with a CO2 equivalence of 25. That means one CH4 molecule in the atmosphere is as bad as 25 CO2 molecules – over a 100-year time frame. Expressed over a shorter time frame, the CO2 equivalence of CH4 gets bigger and bigger. Expressing things using the standard 100-year time frame is all well and good and makes sense if you are a scientist. However, if you are making policy and are not so well versed in CO2 equivalence, it might be very easy for you to gloss over the fact that reducing CH4 emissions right now could have a highly significant impact on climate change in the near future – say the next 10 years. This would be before everyone has had time to go out and buy the Chevy Volt or Nissan Leaf and before we have figured out cold fusion.
It would also suggest that fugitive emissions of CH4 from animal manure lagoons and landfills would be a logical target to try to stop quickly. I’ve just come from the BioCycle West Coast Conference in San Diego where I learned about all of the rigor for animal waste lagoon cover protocols in order for these covers to qualify for carbon credits. These include monitoring requirements, and annual visits from verifiers. Installing a cover makes financial sense for a dairy operation with 4,000 head, but not so much for those with less than 1,500. Fifteen hundred is still a significant amount of cows, well above family farm status.
Perhaps if CH4 had a global warming potential of 75, based on a 25-year time frame, the benefits of covering those lagoons would be recognized. Perhaps also if the 25 year time frame was used for CH4, the argument that landfills produce green energy would not get much credence as a justification to overturn yard trimmings bans. The impact of fugitive CH4 emissions would be enough to keep yard trimmings in compost piles where they belong.

IMPACT ON SOIL CARBON CREDITS
The other thing I’d like to point out about the 100-year time frame is the impact it has on soil carbon credits. There is still a perception out there that adding carbon to soils provides only very transitory storage. Many people think that carbon added to soils is gone within five years. So you can imagine how that pencils out for credits for soil carbon when the 100-year time frame is brought into play. Some people go so far as to start liking biochar more than compost.
The truth is that average residence time for soil carbon is 10 to 32 years, well under the 100-year time frame. But that is the average residence time for one organic molecule, and carbon cycles back and forth from the atmosphere to the soil every year. If you increase the amount that stays in the soil, through organic amendment addition or improved management practices, you may not be keeping that one piece in place for 100 years, but you are making sure that more of those organic molecules stay put each year. And if you have ever read this column before, you are likely to be able to recite from memory the benefits of increasing soil carbon concentrations.
What we must do soon is switch from the need to justify protocols and carbon credits based on the conservative 100-year time frame to behaviors that provide reductions in atmospheric emissions that can be verified over a shorter time period. Atmospheric CO2 concentrations keep going up and the 100-year time frame may not be a luxury that we can stay fixated on for much longer. Perhaps a compromise position would be IPCC or some other type of governmental recognition of the benefits associated with practices that provide significant short-term changes in the carbon balance. These practices may not fit current criteria for longevity but offer a rapid response to an impending crisis.

Sally Brown, Research Associate Professor at the University of Washington (slb@u.washington.edu), authors this monthly column on the connections of composting, organics recycling and renewable energy to climate change.