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Geologic Column

Why Fester? Let's Sequester!
Fred Schwab

A burst of enthusiasm for coal as a way out of the world's energy bind initially inspired this column. Coal is inexpensive, plentiful and widespread (see Geotimes, September 2006). The reserves-to-production ratio for both the world and North America is two centuries, for South and Central America almost four, and for the former Soviet Union more than five. And unlike oil and natural gas, significant coal deposits occur on all continents and in many nations.

I almost convinced myself that with the oil epoch concluding and the nuclear option arguably flawed, coal could be our interim "default fossil fuel of the future." I thought that coal, along with oil shale, might prolong the fossil-fuel age and permit a smooth transition to a future of renewable, unlimited hydrogen-power and controlled nuclear fusion.

I've had second thoughts. Coal is filthy! "Ultrafines" (particles less than 1 micron in diameter) produced by burning coal are responsible for 24,000 deaths annually according to the American Lung Association. In the United States alone, coal-fired power plants produce 130 million tons per year of combustion waste (fly ash, bottom ash, scrubber slush) laced with toxic metals like mercury. More importantly, coal combustion generates two-thirds of the sulfur dioxide, 22 percent of nitrogen oxide, and 40 percent of the carbon dioxide injected into the atmosphere according to Jeff Goodell's book Big Coal: The Dirty Secret Behind America's Energy Future. Coal-fired power plants planned globally through 2030 will pump as much carbon dioxide into the atmosphere as has been pumped out since the Industrial Revolution began, according to David G. Hawkins, director of the Climate Resources Defense Council, and colleagues.

Technology can help some. "Supercritical boilers" (so-called because they produce hotter steam than conventional boilers) reduce carbon dioxide emissions 25 percent. Mixing biomass with coal lowers emissions an additional 20 to 25 percent. Even with these improvements, however, burning coal sends nearly 10 billion tons of carbon dioxide into the atmosphere each year. New processes such as integrated gasification combined cycle technology (also called IGCC, which involves converting coal to an easily transportable liquefied mix of hydrogen and carbon suitable for spinning turbines) can reduce emissions, but these plants cost substantially more.

I now realize that my brief infatuation with coal, stemming from a desire for a quick and easy way out of the energy crisis, is misplaced. I momentarily ignored what is fashionably referred to as "an inconvenient truth," which is that all fossil fuels are dirty. Switching from one fossil fuel to another on the basis of political, economic, strategic or practical reasons does little to reduce greenhouse gas emissions. Something must be done about them to mitigate climate change. So instead of looking toward another energy source, I began to examine carbon dioxide sequestering, the capture and storage technology that removes anthropogenic carbon dioxide from the atmosphere.

Merriam-Webster's Collegiate Dictionary defines sequestering as segregating, isolating or separating. Many techniques exist to sequester carbon dioxide in three available repositories: the biosphere, the ocean and underground.

When considering the biosphere, the simplest solution offered is to simply plant more trees. A "green revolution" maximizing the density of photosynthesizing plants increases the amount of carbon dioxide removed from the atmosphere. Methods also exist to increase the quantity of carbon dioxide stored in biomass and soil, to retard soil's ability to emit gas, and to improve the ability of deserts and degraded lands to sequester carbon.

Seawater, which already soaks up one-third of industrial carbon dioxide, can be an even larger sink. Past experiments toyed with the idea of adding iron to surface water to fertilize it, which increases the population of phytoplankton and the animals that feed on them. As they die and sink with the carbon contained in them, the ocean effectively absorbs more gas, albeit with unwanted side effects. Another seawater sequestration method is to inject the gas directly into deep (greater than 1,000 meters) water, where it sinks because of its higher density. This makes seawater slightly more acidic, but atmospheric carbon dioxide already does this to surface water.

Carbon dioxide gas emissions can also be trapped, transported, and directly slotted to geologic formations — for example, depleted oil and gas reservoirs, deep coal seams and saltwater aquifers, or seafloor sediments. Researchers worldwide are testing these possibilities (see Geotimes, October 2006).

My new perspective has made me, at least tentatively, a booster of sequestering. The fossil-fuel epoch, which requires us to mine and pump 7 billion tons of carbon annually, will certainly continue for the short and intermediate term. However, the rise in atmospheric carbon dioxide from its pre-Industrial Revolution historic norm (280 parts per million) to its 2005 level of 380 parts per million cannot continue, irrespective of whether or not fossil fuel burning is the culprit. Carbon dioxide emissions will double by 2056, if the present growth rate continues unchecked, and drastic climate changes could result. Even if global action is taken now to check the emissions rate, the concentration could still approach 600 parts per million (more than double the pre-industrial level), according to a September article in Scientific American by Robert H. Socolow and Stephen W. Pacala.

The carbon dioxide problem must be dealt with immediately, even as we move to new technologies. Renewable energy will help modestly, and substantial conservation (especially higher mileage per gallon standards) will probably help more.

Hawkins of the Climate Resources Defense Council estimates that rapid implementation of carbon sequestration technology would cost $1.8 trillion (in 2002 dollars), or 0.07 percent of the gross world product. He says that such technology can grow rapidly, spurred by mandatory carbon dioxide release penalties (or emissions reduction credits) at roughly 12 percent annually after 2020. For comparison, in the heyday of industrial expansion from 1956 to 1980, nuclear energy expanded at 40 percent annually.

We're already festering. Let's consider sequestering!


Schwab is a professor of geology at Washington and Lee University in Lexington, Va. E-mail: schwabf@wlu.edu.

Links:
"Coal’s Staying Power," Geotimes, September 2006
"Giving carbon a deep-sea burial," Geotimes, October 2006

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