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Editor's Note: We are posting this feature from our September 2006 issue in light of the Obama administration's renewed focus on how to use the most abundant--and dirtiest--fossil fuel, coal, without overloading the atmosphere with greenhouse gases.
More than most people realize, dealing with climate change means addressing the problems posed by emissions from coal-fired power plants. Unless humanity takes prompt action to strictly limit the amount of carbon dioxide (CO2) released into the atmosphere when consuming coal to make electricity, we have little chance of gaining control over global warming.
Coal—the fuel that powered the Industrial Revolution—is a particularly worrisome source of energy, in part because burning it produces considerably more carbon dioxide per unit of electricity generated than burning either oil or natural gas does. In addition, coal is cheap and will remain abundant long after oil and natural gas have become very scarce. With coal plentiful and inexpensive, its use is burgeoning in the U.S. and elsewhere and is expected to continue rising in areas with abundant coal resources. Indeed, U.S. power providers are expected to build the equivalent of nearly 280 500-megawatt, coal-fired electricity plants between 2003 and 2030. Meanwhile China is already constructing the equivalent of one large coal-fueled power station a week. Over their roughly 60-year life spans, the new generating facilities in operation by 2030 could collectively introduce into the atmosphere about as much carbon dioxide as was released by all the coal burned since the dawn of the Industrial Revolution.
Coal’s projected popularity is disturbing not only for those concerned about climate change but also for those worried about other aspects of the environment and about human health and safety. Coal’s market price may be low, but the true costs of its extraction, processing and consumption are high. Coal use can lead to a range of harmful consequences, including decapitated mountains, air pollution from acidic and toxic emissions, and water fouled with coal wastes. Extraction also endangers and can kill miners. Together such effects make coal production and conversion to useful energy one of the most destructive activities on the planet.
In keeping with Scientific American’s focus on climate concerns in this issue, we will concentrate below on methods that can help prevent CO2 generated during coal conversion from reaching the atmosphere. It goes without saying that the environmental, safety and health effects of coal production and use must be reduced as well. Fortunately, affordable techniques for addressing CO2 emissions and these other problems already exist, although the will to implement them quickly still lags significantly.
Geologic Storage Strategy
The techniques that power providers could apply to keep most of the carbon dioxide they produce from entering the air are collectively called CO2 capture and storage (CCS) or geologic carbon sequestration. These procedures involve separating out much of the CO2 that is created when coal is converted to useful energy and transporting it to sites where it can be stored deep underground in porous media—mainly in depleted oil or gas fields or in saline formations (permeable geologic strata filled with salty water) [see “Can We Bury Global Warming?” by Robert H. Socolow; Scientific American, July 2005].
All the technological components needed for CCS at coal conversion plants are commercially ready—having been proved in applications unrelated to climate change mitigation, although integrated systems have not yet been constructed at the necessary scales. Capture technologies have been deployed extensively throughout the world both in the manufacture of chemicals (such as fertilizer) and in the purification of natural gas supplies contaminated with carbon dioxide and hydrogen sulfide (“sour gas”). Industry has gained considerable experience with CO2 storage in operations that purify natural gas (mainly in Canada) as well as with CO2 injection to boost oil production (primarily in the U.S.). Enhanced oil recovery processes account for most of the CO2 that has been sent into underground reservoirs. Currently about 35 million metric tons are injected annually to coax more petroleum out of mature fields, accounting for about 4 percent of U.S. crude oil output.