Many of you have obtained the model/calculator for the
environmental benefits of recycling and composting from me. Because of
the great dialogue on composting versus incineration on these list serves, I
thought I should mention again that the model does include in the environmental
benefits of composting the upstream pollution prevention from reduction in the
use of synthetic fertilizers and pesticides, and the carbon sequestration
benefits of compost applications and the resultant healthier soils and plants.
The version I sent around assumes that compost use offsets
50% of the average level of synthetic fertilizer and pesticide use on home
lawns and gardens. The model can calculate any level of offset between 0%
and 100%. The model also takes into account the build up of carbon in the
soil from the use of compost, both as a result of the addition of carbon in the
compost itself and as a result of the increased humus formation as a result of
better plant growth.
I picked the 50% fertilizer and pesticides offset estimate based
on the observation that someone who buys compost for their lawn or garden is
not likely to continue to buy the same amount of synthetic fertilizers and
feed/weed type of products. One might argue that the offset should be
higher. My usual tactic in the calculation of environmental benefits is
to make assumptions that are if anything biased toward the burn or bury
proponents. The results still come out favoring recycling and composting,
and it’s then hard to make the case that my analysis is biased toward
recycling and composting. However, one could run the model at 100% offset
of synthetic fertilizers to see how much additional benefits accrue from going
The offset assumption for pesticides is also 50% in the
baseline model. Some of this is from the reduction in purchases of
synthetic fertilizers that include herbicides (weed ‘n feed
products). Some is from the reduced need for herbicides and pesticides due
to the stronger plants that result from a natural lawn and garden care
The carbon build up estimate is from EPA/s WARM model and
the supporting document Solid Waste Management and Greenhouse Gases: A Life
Cycle Assessment of Emissions and Sinks (3rd edition, Sept 2006).
The synthetic fertilizer and pesticide offsets are based on a study that an
economist at Seattle Public Utilities, Jenny Bagby, and I did on backyard
composting and natural lawn and garden care. That study has been peer
reviewed and accepted for publication in the International Journal of Life
Cycle Analysis. The article is published online awaiting its turn in the
queue for publication in the printed journal. The abstract can be found
at http://184.108.40.206/sj/lca/abstract/doi/lca2007.07.350 .
One other point – the model includes other
environmental benefits in addition to climate change benefits from recycling
and composting. It’s important to remember that human toxics and
carcinogens, ecosystem toxics, acid rain, smog, ozone depletion, habitat
alteration, species biodiversity, and water nitrification impacts are also
reduced by recycling and composting. In total these other impacts are of
at least equal if not greater importance than climate change.
Many thanks and much appreciation to those of you that are
out there everyday promoting clean and green behaviors. At some point we’re
bound to reach a tipping point away from our chemically drowned lifestyles.