Poor rural regions could be particularly at risk as residents go back to the old habit of lignite coal heating, prevalent under the polluted skies of the pre-1989 communist regime, to cope with bills that are expected to skyrocket an average 17.4 percent. In the wake of rising prices on world markets, the Energy Regulation Office announced the expected natural gas rate increase Aug. 30. A further hike is expected in January.

"If several dozen households return to coal in one small community, it would represent a local or a regional disaster," says Miroslav Hájek, head of the public support department at the Environment Ministry.

Hájek, whose department promotes the use of renewable energy sources, says the danger is greatest in regions where residents have lower incomes and can easily obtain cheap coal, such as Krušné hory, the mountainous region in northwest Bohemia, or the Ostrava area of north Moravia.

Though many of the forested areas in regions like Krušné hory are still recovering from years of damage related to coal burning, some environmentalists say a return to lignite for domestic heating will primarily damage human health rather than forests.

"This is a problem especially in small villages because it will heavily increase local air pollution, with all the negative health effects that leads to," says Vojtěch Kotecký of Friends of the Earth. Settlements in valleys with limited air circulation will be particularly exposed to lingering brown coal smoke, he adds.

Many homes in bigger cities receive hot water piped from heating plants, including plants powered by coal, but they often have built-in filters to reduce pollution.

Homes in small villages, on the other hand, are not likely to have such systems to cut down on harmful emissions caused by burning coal in a stove or furnace.

While it's impossible to gauge how many people could return to burning coal this winter, Hájek believes those with higher incomes will continue to use gas.

"It is true that the price of gas will be higher, but price is not everything. ... We cannot underestimate the psychological factor. Coal is dirty, you need a place to store it and the manipulation of coal involves a lot of effort," he says.

In one way the situation may have environmental benefits, Hájek adds. Many people may simply try to use less energy and insulate their homes more efficiently.

Tomáš Chmelík, director of the Environment Ministry's climate-change unit, says that people tend to use the cheapest fuel. "The question is if somebody who changed from coal to natural gas can easily change back if natural gas prices increase."

According to the Association for District Heating, 57 percent of households in the countryside use gas heating while 25 percent use coal. In cities only 3.3 percent use coal while 36.6 percent use gas.

An average household that uses gas for heating and cooking will pay 4,700 Kč ($194) more a year after the October price hike, according to the Czech News Agency.

"It is hard trying to convince people to think ecologically when they have to think economically first," says Josef Čapek, director of the forest management office of Jáchymov, a small town in the foothills of the Krušné hory region.

The Karlovy Vary region in west Bohemia, including Jáchymov, has around 10 percent unemployment and the lowest salaries in the country, says Čapek, adding that even current gas prices are too high for him; he uses wood to heat his house.

Meanwhile, Jaroslav Formáček, deputy mayor of Boží Dar, a popular tourist destination in Krušné hory, does not believe residents will return to using coal on a large scale.

"The problem we are facing is a little different," he says, explaining that the municipality has recently completed installation of gas-supply pipes.

"The people who still use coal and intended to start using gas instead will now think twice about it."