Coal exports, a favorite topic here at Wonkblog, have become a hot environmental issue of late. Coal use is shrinking in the United States thanks (in part) to cheap natural gas. So coal companies are building terminals in the Pacific Northwest to ship their surplus coal to places like China.

(Muhammed Muheisen/AP)

So here’s a question: Would blocking these export terminals have any impact on the staggering growth in coal use in places such as China? Actually, yes: There’s some evidence that it could matter a fair bit at the margins.

At first glance, it may look like the United States couldn’t possibly have much sway over China’s coal-hungry habits. China, after all, has plenty of its own coal, boasting the second-largest reserves in the world. In 2010, the country imported less than 5 percent of the coal it used from overseas. And the United States makes up a tiny sliver of this market — because of how Chinese ports and rail networks are set up, China still gets most of its imported coal from Indonesia and Australia:

Still, as a recent and fascinating report (pdf) from the Carnegie Endowment explains, Chinese coal imports are likely to grow enormously in the coming years. For one, Chinese coal use has been growing at a rate of nearly 6 percent each year. And China’s domestic production can’t keep pace, thanks to railroad and shipping bottlenecks from mining centers in Shanxi, Shaanxi and Inner Mongolia provinces.

What’s more, the Carnegie report notes, the Chinese government is becoming increasingly sensitive to the ecological damage wrought by domestic coal mining — as well as to the growing number of protests over unsafe mining conditions. According to official statistics, 6,027 Chinese miners died in 2004, though the real number is probably higher. There are real costs to ramping up production in China.

As a result, China will likely try to import a growing share of its coal in the coming years. Much of that will likely come from Indonesia and Australia, since China’s import infrastructure is geared toward those two regions. But many analysts expect the United States to play an increasingly crucial role in coming years. (To date, the U.S. has been supplying China with just small amounts of coking coal, which is used for iron and steel production and which is less readily available in China.)

And if American coal starts pouring into China, that will help keep prices down. If that happens, Chinese power plants and factories will burn even more coal and use the stuff less efficiently than they otherwise would. Grist’s David Roberts points to a recent paper (pdf) by Thomas M. Power, a former economics professor at the University of Montana, finding that Chinese coal habits are highly sensitive to prices:

Opening the Asian import market to dramatic increases in U.S. coal will drive down coal prices in that market. Several empirical studies of energy in China have demonstrated that coal consumption is highly sensitive to cost. One recent study found that a 10 percent reduction in coal cost would result in a 12 percent increase in coal consumption. Another found that over half of the gain in China’s “energy intensity” improvement during the 1990s was a response to prices. In other words, coal exports will mean cheaper coal in Asia, and cheaper coal means more coal will be burned than would otherwise be the case

To some extent, U.S. exports are already having an impact. Coal prices in Asia hit a 16-month low recently, thanks to an overflow of coal from the United States and Colombia. And the Pacific Northwest hasn’t even seriously ramped up its exports yet. (India is another possible market for U.S. producers: As the New York Times recently reported, Indian power companies have been trying to import coal from abroad rather than deal with India’s dysfunctional mining industry, but they’ve been deterred in the past by high prices.)

Now, the global coal markets are complex and it’s still not clear exactly how important U.S. coal will prove to be for countries like India or China. As Michael Levi of the Council on Foreign Relations points out, a lot depends on whether U.S. coal augments or displaces production from countries like Indonesia.

Still, at the margins, supply and demand matters. The point of Thomas Power’s paper is that a deluge of coal from the United States will, in the end, cause Asia to use more coal. Countries like China will have less incentive to develop alternative energy sources or become more efficient. And that, in turn, will mean more heat-trapping greenhouse gases in the atmosphere than there otherwise would be. To put this in perspective, 150 million tons of coal produces about as much carbon dioxide as 60 million cars.

That’s why many environmentalists are looking for ways to, as Roberts puts it, “Keep the damned coal in the ground.” Blocking U.S. export terminals in the Pacific Northwest is one such strategy. Of course, coal-mining firms like Arch and Alpha, now struggling to keep their stock prices aloft, aren’t likely to sit idly by while this happens.