On a planetary scale, the greenhouse effect occurs when the sun's rays pass through greenhouse gases, such as carbon dioxide, in the atmosphere. The earth warms, and that warmth is absorbed by the carbon dioxide, which does not allow it to escape into space. When the amount of greenhouse gases in the atmosphere is too high, the result is climate change. The carbon dioxide released by burning wood has minimal impact on the greenhouse gas effect.
Release of Carbon Dioxide
Trees use photosynthesis to change the energy they get from the sun, the carbon dioxide they get from the air, and the water and minerals they get from the soil into stored energy. That energy is stored in the form of cellulose. When we burn wood, we release the energy the tree got from the sun and the carbon dioxide it originally used to produce the wood. According to Bernard Cohen, Professor Emeritus of Physics at the University of Pittsburgh, this release of carbon dioxide does not contribute to the greenhouse effect because the wood was created from carbon dioxide. Burning the wood doesn't add any new carbon dioxide to the system.
Carbon Sequestration
Chopping down trees prematurely can, however, release unnatural amounts of carbon dioxide into the atmosphere. Forests are natural carbon sinks. In other words, they take carbon dioxide from the air and bind it in a process known as carbon sequestration. In an unmanaged forest, carbon dioxide is bound as the trees grow and then released as the trees die and rot. If trees are cut down and burned at a faster rate than the natural death and decay rate, an unnaturally large burst of carbon dioxide is released into the air. According to the EPA, deforestation is "a significant source of carbon dioxide emissions globally, but a minor source in the U.S." However, the practice of burning biomass for fuels is growing. If industrial-scale wood burning were to become more common in the United States, the challenge of balancing levels of carbon sequestration would grow as well.
Other Greenhouse Gases
When wood burns completely efficiently, its release of greenhouse gases is carbon neutral. When wood burns inefficiently, however, it may also release other gases as well. The two other main greenhouse gases--methane and nitrous oxide--are produced when wood is burned inefficiently. According to "Air Emissions from Residential Heating," the quantities of these other greenhouse gases by residential wood-burning is negligible.
Actual Effects
It is theoretically possible for the practice of cutting and burning wood to have a greenhouse gas effect. In "real life," however, that effect is not very large. According to "Air Emissions from Residential Heating," wood burning in a residential setting has the lowest greenhouse impact per unit of energy of any of the common space heating options. The effect is significantly lower than space heating using electricity produced by coal and petroleum.
References
- Bernard Cohen: Environmental Problems with Coal, Oil, and Gas
- Arizona State University, Center for Bioenergy & Photosynthesis: Why Study Photosynthesis?
- Natural Capital Iinitiative at Manomet: Biomass Sustainability and Carbon Policy Study
- Renewable Energy Policy Network: Renewables Global Status Report; 2006 Update.
- "The Proceedings of a U.S. EPA and Air Waste Management Association Conference"; Air Emissions from Residential Heating; James E. Houck, et al; 1998
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