How's that "war on coal" going? It all depends where you look. In the United States, coal power continues to face intense pressure from cheap natural gas and strict air-pollution rules. But in the rest of the world, coal use keeps soaring.

A coal-fired power plant in Brilliant, Ohio. (Washington Post) A coal-fired power plant in Brilliant, Ohio. (Washington Post)

Case in point: A recent study (pdf) from the Union of Concerned Scientists found that 329 coal units in the United States are no longer competitive with natural gas or wind power and face possible retirement in the years ahead. They won't all get shut down, but they're facing heavy pressure. (The study was published in Electricity Journal.)

That's a very large number: Back in 2011, there were 1,191 coal generation units operating in the United States. Since then, 288 have already either retired or are set to be retired. That means more than one-third of the remaining U.S. coal units are now at risk of closing, under pressure from alternative energy sources and pollution rules by the Obama administration. (Even so, coal is projected to remain a significant source of U.S. electricity in the decades to come.)

But those trends put the United States at stark odds with the rest of the world. A separate report out Monday from the International Energy Agency on that global coal demand is seemingly insatiable — driven by rising consumption in nations like China and India. The agency predicts coal use will keep growing at a 2.3 percent clip over the next five years.

Given that coal burning is the world's biggest source of greenhouse-gas emissions, that's bad news for those worried about global warming. “Like it or not, coal is here to stay for a long time to come,” said Maria van der Hoeven, the agency's executive director.

The decline of coal in the U.S.

Here's a map from the Union of Concerned Scientists study showing where the 329 U.S. coal units now most at risk are located. They represent about 59 gigawatts of capacity in all — or 17 percent of the 347 gigawatts in coal capacity the nation had in 2011.

That's significant, since most analysts predict that very few new coal plants will be built in the United States in the next two decades. Here's a more precise breakdown of the numbers:

-- Back in 2011, there were 1,191 coal generation units around the United States with 347 gigawatts of capacity.

-- Already, 138 of those units have been retired over the past two years, representing about 18 gigawatts of capacity. These aging plants were 52 years old, on average, and often it simply wasn't worth upgrading them with modern pollution controls.

-- Another 150 units, or 28 gigawatts, are already scheduled for retirement in the years ahead. That means that roughly 13 percent of the coal capacity in 2011 will soon be retired.

-- The Union of Concerned Scientists study also found that another 329 units, or 59 gigawatts, will struggle to compete with wind or natural gas at current prices. They won't all get shut down, but that means one-fifth of the remaining coal units are now more expensive than available alternatives:

The chart shows a variety of scenarios for coal under different policies. For example, the production tax credit for wind power is set to expire at the end of this year. If Congress extended that credit, even more U.S. coal units would be at risk — some 71 gigawatts of capacity. (Many of the threatened plants would be in Oklahoma and Texas.) Likewise, if policymakers enacted a $20-per-ton carbon tax, that would put half of the U.S. coal fleet at risk of retirement.

The study also separates out the factors at play: About 77 percent of the at-risk coal plants are facing possible retirement due to new rules from the EPA on pollutants like mercury, sulfur dioxide, and particulates. Many plant owners may decide to shutter their older units rather than install costly new control technology. But the remaining 23 percent would likely be at risk even if those EPA rules were repealed tomorrow — they're mainly vulnerable to competition from cheap natural gas and wind.

Global coal demand keeps rising

Now, the landscape looks very different when you look at the rest of the world, however. A new International Energy Agency report finds that coal use increased at an average rate of 3.4 percent per year between 2007 and 2012, driven by countries like China and India.

The IEA expects coal demand to slow down slightly in the years ahead, thanks to a new crackdown on air pollution in China. But the agency is still forecasting 2.3 percent annual growth in coal consumption between now and 2018:

That's why many U.S. coal companies are now paying closer attention to exports. Increasingly, that's where the market is.

It also explains why carbon-dioxide emissions in the rest of the world keep increasing, even as they've fallen here in the United States in recent years. The IEA report estimated that coal consumption accounted for more than 60 percent of the rise in heat-trapping carbon dioxide emissions worldwide since 2000.

In her remarks Monday, Van der Hoeven also noted that small tweaks to the global coal fleet could have a big impact on emissions. For instance, many of the coal-fired plants being built in countries like India and Indonesia still use old, inefficient technology. Simply completing these plants with modern technology, she said, "would save as much CO2 as will be saved by all the wind turbines in Europe."

Alternatively, if countries like China could unlock their own shale gas resources, that would further tamp down on coal power — much as it has in the United States. So far, however, the fracking boom has been slow to spread elsewhere.