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.