Thanks to the scientists at the University of Edinburgh, the public now has a more accurate
portrayal of the subject of terrestrial carbon sinks. Biospheric carbon sequestration, particularly
by forests, really does work. But what is this "sink saturation" that both Pearce and Tipper et al.
talk about? Basically, it's the idea - which is indeed logical - that there must be an upper limit
to the amount of carbon that an ecosystem can sequester, plus the subsidiary and more
practically-important idea that that limit will be reached well before mankind has either (1)
depleted all of Earth's fossil fuel reserves or (2) discovered a more economical non-fossil-fuel
energy source for powering the engines of industry and transportation, which would mean, of course,
that biospheric carbon sequestration would ultimately fail to function as needed to forestall any
global warming that might be occurring (for whatever reason) at that future time.
Clearly, the latter eventuality is indeed possible; but is it likely? Let's take a look at some of
the recent peer-reviewed scientific literature on the subject to see what people working on these
ideas think of them. And let's see how the ongoing rise in the air's CO2 concentration acts to
modify biospheric carbon sequestration processes to make them even more powerful and efficient than
they are currently.
Part III: Atmospheric CO2 Enrichment: Priming the Biospheric Carbon Pump
Consider, first of all, the indisputable fact that more CO2 in the air stimulates greater vegetative
productivity in almost all plants under almost all conditions in almost all situations (Idso and
Idso, 1994). As the air's CO2 content rises, this phenomenon causes ever more carbon to be stored
away each year in the woody tissues of long-lived bushes, shrubs and trees, both above- and
below-ground, where it eventually becomes part of the organic matrix of the soil. But how much more
carbon can be biologically "pumped" into earth's forests and soils? And what about very long time
periods and short-lived plants? Also, what happens when plants eventually die and decompose? And
what happens if the globe does continue to warm for some reason, hastening the decomposition of dead
organic matter and the return of its carbon to the atmosphere? Will these forces overpower the
increased ability of plants to remove CO2 from the air and sequester its carbon in their tissues or
in recalcitrant soil organic matter?
How are agricultural soil sinks treated in the Kyoto Protocol?
Agricultural sinks are acknowledged in the Kyoto Protocol, (particularly in Article 3.4) in a
limited manner. International consensus has not been reached on the role of carbon sequestration in
soils for the first reporting period under the Kyoto agreement. International activities that can
help achieve consensus include workshops focusing on sequestration activities and an
Intergovernmental Panel on Climate Change report currently underway on land use, land use change and
forestry and the potential for greenhouse emission offsets. Keys to gaining international
understanding of carbon sequestration include developing scientifically sound projections of the
potential for sequestration from agricultural activities and developing agreed-upon methods for
determining, reporting and verifying changes in soil carbon stocks.
What is USDA doing to better understand soil sequestration?
USDA research is focusing on understanding the role of agricultural ecosystems in the global carbon
cycle. For example, scientists from USDA's Agricultural Research Service are using state-of-the-art
technology to measure carbon dioxide emissions from soil during tillage and analyzing the rates of
storage of atmospheric carbon dioxide as organic carbon in soils following the adoption of
conservation practices. This research will help determine how much agricultural soils can serve as
sinks for greenhouse gases. Scientists are also measuring the rates of carbon dioxide assimilation
of rangelands to help climate modelers develop better estimates of future atmospheric carbon dioxide
levels. USDA's Natural Resources Conservation Service (NRCS) is focusing on improving the Nation's
soil carbon database. This information is necessary to show how much carbon has been lost and the
potential for future sequestration. NRCS also is developing models to link on farm practices to
carbon sequestration and to assess regional and national carbon sequestration rates. The Forest
Service is developing management practices to increase sequestration and are implementing such
practices on the national forests.
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