The Chinese fires also make a big, hidden contribution to global warming through the greenhouse effect, scientists said. Each year they release 360 million tons of carbon dioxide into the atmosphere, as much as all the cars and light trucks in the United States.

The Chinese mining industry is one of the few in the world
that actively tries to extinguish coal mine fires on a broad scale..

Quantifying the amount of pollution that underground fires create is as difficult as spotting them. The smoke escaping through vents contains carbon dioxide, methane, mercury and at least 40 toxic compounds - "a whole soup of nasty stuff," according to Glenn Stracher, a geologist at East Georgia College in Swainsboro, Ga., who studies the emissions. But that soup's ingredients vary from hour to hour, even vent to vent, and some of the gases also escape through adjacent soil. "It's not like the oil well in the Gulf, where you measure how much is coming out per unit of time," Stracher says. "Making calculations is a tricky business." He and other researchers readily admit that global coal fire emission estimates - 40 tons of mercury spewing into the atmosphere annually, and 3% of the world's annual CO2 emissions - are imprecise. But the negative implications for human health and global warming, they say, are clear.

With that in mind, some countries are investigating whether snuffing the fires could help them earn carbon credits under the Kyoto Protocol, and are stepping up prevention awareness. Though geologic records show evidence of underground coal fires dating to the Pleistocene era, modern-day coal fires are often an unintended side effect of mining operations that open coal seams to oxygen. Once exposed, the coal undergoes a chemical reaction that releases heat. In some climate conditions the coal spontaneously combusts. Otherwise, lightning, wildfires or an ill-placed spark can trigger the blaze. The flames rip inside the buried coal seams at temperatures exceeding 1,000°F, sometimes fed by oxygen trapped in the microscopic spaces between dirt particles. They're also assisted by a process known as subsidence: as the burning coal turns to ash, it causes the overlying ground to crack and collapse, supplying the fire with fresh air.

Extinguishing a fire amounts to a frustrating, expensive version of whack-a-mole. "You put one down, then 300 feet later another one picks up," says Engle. Firefighters can dig up the burning coal or form a break around it, and they sometimes pump ignited seams with cryogenic liquids that absorb enough heat to prevent burning. But large coal deposits can span several miles at 90 feet deep and 100 feet thick, creating a honeycomb of pores that always leaves a few pockets of fire-fanning oxygen. That means the same fire can later reignite — and fighting underground fires doesn't come cheap. The U.S has already spent more than $1 billion battling underground coal fires, according to the Office of Surface Mining. Officials gave up hopes of dousing the extensive Centralia, Pa., fire because the job would have cost more than $600 million — and that was in 1983.

Less expensive alternatives are beginning to hit the market, from special heat-resistant grouts to a fire-smothering nitrogen foam, and other innovative solutions are on the way. "Look, tornadoes and earthquakes are here and gone," Stracher explains, "but these fires will burn for hundreds of years if we don't do something about them." It seems that where there's smoke there is indeed fire, whether we can see the hidden flames or not.

Can't beat them… yet! But we can harness its energy…

In the USA there are approximately 600 coal mine fires that are burning over a period of 80 years. Other underground coal mines fires are located in Russia and in several east European countries. These fires are located at shallow depth and the depth in many cased do not go beyond 400-500 m. The heat energy from these coal fires is not put to use. Yet the Heat Exchanger technology, commonly used in geothermal power generation, can easily be adopted in regions where underground coal mine fires is common. Continuous heat source from burning coal seams underground will provide continuous electric supply and, to some extent, can controls underground coal fires, limit CO2 emission and generate electricity to million rural homes. The technology exists (among others) and all that is required is the will-power to implement them!

1. Upper left image -The steaming hills near Hazard, Kentucky, USA - a coal seam fire that started in 2007.
2. Upper right image - Fire frequently breaks out from a coal mine seam in Browns Branch near Van in Boone County, West Virginia, USA

3. Residents of a Kuli Dhaori or miner's slum, in the Jharia coalfield of India. Children living here with their families play in air polluted by toxic fumes from coal-fire gas while their parents work in the surface-coal mines.

4. Self-ingnited coal seam fire in China