When you think of the vast expanse of wet prairies in Florida’s Everglades, the peat-filled wetlands of Georgia’s Okefenokee Swamp, or the Amazon River Delta, coal isn’t the first thing that comes to mind. But these landscapes are modern-day examples of the enormous, ancient inland seas and dense tropical swamps that turned into today’s coal beds. Much of the world’s coal dates back to the Carboniferous Period, some 318 million years ago, and contains plant matter and fossils from before the era of the dinosaurs.
Coal is America’s mighty rock. Because coal burns at a slow rate for a long time, it’s more efficient as an energy source than other fossil fuels. And the United States is naturally well-endowed with coal resources—25 percent of the world’s coal reserves are within our borders. Coal has been the leading electricity source worldwide, and over the past 10 years it has supplied one-half of the increase in global energy demand, growing even faster than renewables. And now it’s one of the most fiercely disputed fuels.
There is a dark side to coal. It produces more carbon dioxide when burned than other fossil fuels do and adds disproportionately to global climate change. Ecological costs are abundant, too, and range from mountain-top removal mining to air pollution to coal ash spills.
Coal exports from the United States this year are expected to reach 125 million tons, breaking the previous record of 113 million tons set in 1981. And according to the World Energy Council, the world’s coal use is expected to rise 60 percent by 2030, with developing countries responsible for 97 percent of this increase.
To understand the conflicts surrounding coal, it helps to step back and review how we came to have this contested resource. The two main ingredients in the recipe for coal are peat and time. Decayed plant matter and sediment accumulated in large basins in the Earth’s crust to form peat. Over millions of years, layers of mushy peat accumulated in geologic basins and were buried by sediment that accumulated little by little, from stormwater runoff or the wind, for instance. Over time, the basin of sediment sank below the Earth’s surface.
Depending on tectonic forces, such as the stability of the earth’s crust in the area or an uplift in mountain ranges, the peat deposits ended up deep underground or closer to the surface. As the buried sediment compacted under pressure, water was squeezed from the peat, natural heat from the earth’s core baked it, and coal formed, a process called coalification.
Peter Warwick of the U.S. Geological Survey says coalificaiton is like the cartoon image of Superman squeezing a chunk of coal to make a diamond. “It’s the same concept. You need to compact and squeeze this peat to form coal,” he said; coal is just “concentrated carbon.”
The United States had three major coal-forming periods: the Pennsylvanian (318-299 million years ago), which formed the Appalachian coal beds; the Cretaceous (145-65 million years ago), which formed coal in Colorado, Utah, and New Mexico; and the early Tertiary (65-35 million years ago), which led to major coal deposits in Wyoming, Montana, North Dakota, and Texas.
During these three periods, what is now dry land contained large inland seas and lakes. On the edges of these bodies of water were warm, swampy coastal plains that filled in with decaying plants. We don’t have those vast regions today, but places like the warm, wet coastlines of Indonesia and the Okefenokee are now accumulating peat, Warwick says.
During the geologic past, sea level was much higher at times than sea level today. The United States spans part of a continent that was flooded during the major coal-forming times, which led to the formation of broad coastal plains where peat could accumulate, Warwick says. “Add a warm climate and all this contributed to our coal endowment,” added Warwick. It’s a lucky past. Other continents may not have had all these conditions at the time, so peat and coal preservation many not have been as great.
Appalachia and the Illinois Basin have some of the oldest, largest coal deposits. Coal in these areas is found in seams a few hundred feet beneath the earth’s surface, and is mined underground from tunnels or in open pit mines, because it’s mostly deep. This coal east of the Mississippi is primarily a dense, high grade of coal, called bituminous, that contains up to 85 percent carbon. Pennsylvania’s northeast coal fields contain small deposits of the hardest, oldest grade of coal on earth, called anthracite, which is up to 98 percent carbon.
Western coal is younger and a different kind of coal altogether. It’s a much softer version, called sub-bituminous coal, that contains less than 45 percent carbon. Nearly one-half of the coal reserves in the United States are sub-bituminous, and most of it is located in thick beds near the surfaces. While sub-bituminous coal has a lower energy content than bituminous coal, it is mined cheaply in large quantities, making it a low-cost energy source. The Power River Basin in Wyoming, a surface mine, produced 40 percent of all coal mined in the United States in 2011. This coal releases less sulfur dioxide when burned, but power plants need to burn 50 percent more of it to match the higher energy content of Eastern coal.
In 2011, the United States had 259 billion tons of known recoverable coal reserves, more than any other country. But the United States is using less coal itself, so the industry is shrinking even as exports are up. While election campaign rhetoric focused on coal mine job losses in Central Appalachia, a variety of factors play a role in what’s happening to coal. The long, slow decline doesn’t have much to do with whatever economic incentives or regulations are batted about in political speeches. Near-record cheap natural gas has slowed coal use in some regions. In the next four years, 175 small, aging, less-efficient coal generators (accounting for 8.5 percent of total U.S. coal-fired capacity) are expected to close. The plants are located mostly in the Mid-Atlantic and Ohio River Valley regions.
In China and India, coal plants are being built left and right. In Europe, and especially Germany, which is retiring its nuclear power plant fleet, coal is experiencing a renaissance because it’s a cheaper replacement than natural gas.
The coal we burn today was millions of years in the making. We continue to extract and burn vast amounts of it. Given current trends, we’ll run out of it in 225 years or so. In human terms, we have a few generations to figure this out. In geologic time, it’s almost gone.
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