Green-friendly Europe has a dirty secret: It is burning a lot more coal.

Europe’s use of the fossil fuel spiked last year after a long decline, powered by a surge of cheap U.S. coal on global markets and by the unintended consequences of ambitious climate policies that capped emissions and reduced reliance on nuclear energy.

The new dependence on one of the dirtiest fuels shows just how challenging it is to maintain the momentum needed to go green, analysts and officials say, and demonstrates the far-reaching effects of America’s natural gas boom.

In the United States, natural gas is now frequently less expensive than coal for power, so demand for the hard, black fuel has plummeted. Ships are steaming the coal around the world instead. U.S. coal exports to Europe were up 26 percent in the first nine months of 2012 over the same period in 2011. Exports to China have increased, too.

“It’s been very welcome that U.S. greenhouse gas emissions have been going down because of the switch to gas,” said David Baldock, executive director of the Institute for European Environmental Policy in London. “But if we’re simply diverting the coal somewhere else, particularly to Europe, a lot of those benefits are draining away.”

Rise of cheap U.S. coal in Europe

In Germany, which by some measures is pursuing the most wide-ranging green goals of any major industrialized country, a 2011 decision to shutter nuclear power plants means that domestically produced lignite, also known as brown coal, is filling the gap . Power plants that burn the sticky, sulfurous, high-emissions fuel are running at full throttle, with many tallying 2012 as their highest-demand year since the early 1990s. Several new coal power plants have been unveiled in recent months — even though solar panel installations more than doubled last year.

Here in Jaenschwalde, a stone’s throw from the Polish border, the forested countryside quickly drops away into a 300-foot-deep pit stretching for miles. Enormous machines slowly eat away at the earth and shower soft lignite onto a conveyor belt that feeds directly into a nearby power plant. From the precipice of the mine, the 20-foot-tall trucks at the bottom look like Tonka toys.

Last year, the power plant consumed 88,000 tons of lignite a day and generated more electricity than it had since 1981, according to Vattenfall, the Swedish company that runs it. That record is even more impressive given that in 1981, Communist East German officials didn’t have to contend with labor laws or environmental regulations and could run the mines almost every day of the year.

The expansion of lignite mining has stunned some people who live in its path. One community under threat is the tiny hamlet of Atter­wasch, a cluster of 250 people on the edge of a proposed expansion of the Jaenschwalde mine. They might have to leave their homes, as well as their church, whose chapel was built in 1294.

“This church survived the Thirty Years’ War [in the 1600s], two world wars and socialism,” said Mathias Berndt, the senior pastor at the church, which is festooned with anti-coal-mining protest banners. “Now a free country is coming and saying, ‘Good for you, but now you have to move.’ ”

Demand for coal in Germany has been rising since a May 2011 move to phase out nuclear power by 2022. The shutdown was spurred by the nuclear meltdown at the Fukushima Daiichi plant in Japan as well as long-standing German concerns about safety. But nuclear energy, which is low in greenhouse gas emissions, has been partially replaced by brown coal. Lignite supplied 25.6 percent of Germany’s electricity in 2012, up from 22.7 percent in 2010. Hard black coal supplied an additional 19.1 percent last year, and it was also on the rise.

Germany phases out nuclear

“The faster phaseout [of nuclear energy] has led to an increased fallback on lignite,” said Thomas Bareiss, a member of Germany’s parliament and the energy policy coordinator for the ruling Christian Democratic Union party. “Lignite will surely play an important role for our energy mix over the next two or three decades.”

But the rise of coal has posed a challenge to Germany’s tough environmental goals. By 2050, the country aims to generate 80 percent of its electricity from renewable sources, allowing steep reductions in greenhouse gas emissions. Green advocates worry that if Germany’s extensive — and pricey — support for renewable energy such as wind and solar power diminishes, coal might further fill in the gap.

Energy companies say that the two forms of power generation can live together for now. Lignite plants, they say, are an economical way to meet demand at times when the wind isn’t turning windmills and the sun isn’t warming solar panels. But officials acknowledge that with the ambitious energy goals, coal’s future might be limited.

Germany “has to change completely,” said Hartmut Zeiss, head of mining for Vattenfall Europe. “The question now is how long it will take and what we can afford.”

In other European countries, the quick rise of coal has surprised people who thought it was a waning industry. In Britain, domestic coal production nearly died in 1984 during a bitter, year-long miners’ strike that pitted Prime Minister Margaret Thatcher against the once-powerful unions. Domestic production is still moribund, but in the first nine months of 2012, imports of U.S. coal were up 73 percent from the same period in 2011.

The few remaining domestic coal mines say they can’t compete, and newspaper headlines have harped on the irony.

“The future looks a bit gloomy,” said David Brewer, director general of the Confederation of U.K. Coal Producers.

Consumption of coal also has leapt in Spain and Italy, with much of it supplied by the United States. That comes despite extensive efforts to harness Spain’s sun and Italy’s wind in the name of power production. Consumers, slammed by sky-high unemployment, have been particularly sensitive to energy prices.

U.S. shift to natural gas

The abundance of American coal on international markets has been an unintentional side effect of the rapid rise of new drilling techniques for natural gas in the United States. Hydraulic fracturing, or “fracking,” has opened up new reserves so vast that the United States will soon become a net natural gas exporter, slashing the country’s reliance on costly oil imports. U.S. manufacturers are looking with glee at cheaper natural gas prices. And because natural gas is cleaner than coal, U.S. greenhouse gas emissions from electricity generation have dropped to their lowest levels since 1992.

Now, U.S. coal is spreading around the world instead, pushing down global prices. In Europe, that has raised fears among environmentalists that the cheap natural gas in the United States has simply led to higher overall fossil fuel consumption.

One big part of the problem, experts and officials say, is Europe’s cap-and-trade system, which aims to reduce European Union-wide industrial greenhouse gas emissions by 20 percent by 2020. The system is the centerpiece of Europe’s green policies. But the program, which charges industries for permits to emit greenhouse gases, no longer serves as a major disincentive to pollute. Industrial production fell dramatically during the economic crisis, so overall greenhouse gas emissions remain well underneath the cap, and they are still falling. The price per ton of carbon emissions is barely more than a tenth of its 2008 peak. Energy companies, who must plan decades in advance, have shied away from investing in gas-fired power plants because they are not profitable in comparison to coal.

Europe’s coal use might soon taper off, some experts say. And European lawmakers are trying to prop up the cap-and-trade system by setting more ambitious targets for 2025 and 2030. That would quickly send the price of permits up and make coal less competitive with greener forms of energy.

“The higher the price is for carbon, the worse the business case is for coal, and the better it is for gas,” said Hubertus Bardt, an energy expert at the Cologne Institute for Economic Research.

In addition, American mines might cut back on their production because of the lower prices, thus tightening the global supply and making coal less competitive in comparison to other energy sources, according to analysts.

For now, confronted with a glut of newly available fossil fuel, environmentalists are trying to decide whether it’s best to try to keep it underground.

“What we want to achieve is a reduction in the total quantities of the emissions of greenhouse gases,” said John Broderick, a research fellow at the Tyndall Center for Climate Change Research in Manchester, England. “If we’re serious about this, we would be looking to disincentivize the extraction of fossil fuels.”

Petra Krischok in Jaenschwalde, Germany, and Eliza Mackintosh in London contributed to this report.