(Conservation Currents,
Northern Virginia Soil and Water Conservation District, September
2003)
Over the past decade, global warming has become
one of the defining environmental issues facing this and all
other nations. While research consistently indicates the existence
of this global trend, little has been done to combat it. Part
of the reason for this is our strong dependence on energy derived
from fossil fuels, such as coal and oil.
While many in government recognize the need
to change our patterns of energy consumption in the long run,
there is also the recognition that phasing out fossil fuel usage
will be a painful process that could seriously hurt the present
economy. The economic damage done could be lessened, or even
eliminated, if alternative technologies, such as solar or wind
power, were to advance to a point where they could rival or
even undercut the cost of fossil fuels.
While advances in alternative technologies
have greatly reduced the cost of these energy sources, fossil
fuels are still the cheapest energy sources in most parts of
this and other countries. In addition, the massive infrastructure
necessary to transport fossil fuel-derived energy to customers
(think of the millions of gas stations in the United States)
is already in place. For the most part, alternative energy sources
lack this infrastructure.
As the need for cleaner sources of energy
becomes more and more apparent, investment in alternative technologies
and physical infrastructure will certainly increase, but it
may be decades before fossil fuels can be supplanted as our
principal source of energy. Therefore, it may be practical to
find a short-term solution that will bridge the gap between
the fossil-fueled present and the alternative-energy-powered
future. The quick fix for global warming may lie in the soil.
Soil is what is known as a carbon sink, which
means that it can capture and hold onto carbon for years rather
than allowing its release as C02 into the atmosphere. Carbon
primarily enters the soil as dead plant and animal material
(leaves, twigs, carcasses etc.), feces, or C02 dissolved in
rainwater. Soil microorganisms quickly get to work breaking
down this material, and while some of it is subsequently released
as C02, quite a bit of it is transformed into durable partially
degraded organic material called humus. The carbon in humus
can remain untouched for hundreds, sometimes even thousands,
of years. If properly managed, the humus level, and thus the
carbon level, of soils can increase with time.
In order to see significant carbon increases,
a soil must be protected. This means shielding the soil from
oxidation. Oxidation occurs when a soil is sifted and broken
up, such as when it is plowed. Plowing exposes a lot of the
subsoil humus to the atmosphere, and the increased oxygen levels
allow for quicker breakdown of organic material and thus more
C02 output. Therefore, to increase the levels of carbon stored
in soil and combat the rise of C02 in the atmosphere, national
policies should emphasize conservation tillage or no-plow farming
techniques. If large swaths of soil are protected, it is possible
that atmospheric C02 levels could be stabilized or even reduced
in the short term while more permanent alternative energy technologies
are perfected.
Soil carbon sinks appear to be a promising
ally in the fight against global warming. It is estimated globally
that soils store 1,500 gigatons (1 gigaton = 1 billion tons)
of carbon. By comparison, terrestrial plants store 560 gigatons,
and the atmosphere holds 720 gigatons. However, soil carbon
sinks should not be seen as a permanent solution. Soils can
only hold so much carbon, and it is generally thought that under
no-till management, the average soil will reach its maximum
carbon content within fifty years. On the other hand, a lot
of technological change can occur within fifty years, and perhaps
by the time the soil carbon sink has been exhausted, reliable
and clean fuel sources will have rendered fossil fuels obsolete.
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