Charcoal warms the whole world

The greenhouse gases spewed out during the production of charcoal in developing nations may warm Earth’s atmosphere more effectively than would the carbon dioxide generated by the burning of fossil fuels, according to new research. That’s the case even though charcoal is made from wood that removed globe-warming carbon dioxide from the atmosphere as it was growing.

Many parts of the world, especially some in Africa and Southeast Asia, use charcoal-fed fires for heating, cooking, and industrial processes. For example, 9 percent of the energy consumed in Kenya comes from charcoal. In Brazil, almost 40 percent of the wood gathered for fuel ends up as charcoal destined for the pig iron and steel industries.

Worldwide, between 26 million and 100 million tons of charcoal are produced each year. Estimates vary widely because much of the fuel is made by individuals and therefore isn’t easy to track, says Kirk R. Smith, an environmental scientist at the University of California, Berkeley.

Charcoal is produced by burning wood, brush, or grass with a limited supply of oxygen. Smith and his colleagues studied the charcoal-making process in Kenya, where the fuel is made in earth-covered mounds that smolder for up to 10 days, and in Brazil, where production takes place in several types of large kilns. Although charcoal burns more cleanly than wood, the researchers found that inefficiencies in its manufacture result in much of the carbon in the original wood literally going up in smoke before the resulting fuel ever reaches the consumer.

Depending on the production method, only 37 to 69 percent of the wood’s carbon remains in the charcoal, say the researchers. On average, 27 percent of the carbon returns to the atmosphere locked in carbon dioxide molecules. Significant amounts of the carbon leave the wood in methane or carbon monoxide molecules. In the long run, both of these gases warm Earth’s atmosphere more efficiently than carbon dioxide does, Smith notes. Charcoal making also produces nitrous oxide, another potent greenhouse gas.

In the Oct. 27 Journal of Geophysical Research, the researchers contend that with the heat-absorbing characteristics of all these gases included, the combination of producing and burning charcoal warms the atmosphere more than the burning of fossil fuels does. Many developing nations could reduce their total greenhouse-gas emissions simply by replacing peoples charcoal cooking stoves with ones fueled by propane, Smith says.

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