Global Warming: Does the Solution Lie in the Soil?


(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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