The couple, who live in a tiny house in one of the Chinese traditional "hutong" alleyways, would love to use a cleaner fuel but can not afford it on their meagre incomes.

"Of course we want to switch to electricity, it's cleaner, more hygienic and convenient, who doesn't know that?" 66-year-old Zeng asked.

"But how will we manage without these? This lot cost 1,000 yuan (135 dollars) and will last me the whole winter," he said, pointing at the coal briquettes piled up to over a metre (three feet) high.

Switching to electricity would cost him at least double the amount of money, he said.

His neighbour Wang Suying, also 66, said she could not switch to gas without the infrastructure at her brick-built home.

"Coal is a necessity to us. How else can we keep warm?"

The tales of Zeng and Wang offer a small illustration of the difficulties facing China -- from individuals to mega industries -- as it seeks to cut back on coal, which emits carbon dioxide blamed for global warming.

The Chinese government has set ambitious goals to rein in the country's output of carbon dioxide and other greenhouse emissions.

It has pledged to make renewables around 15 percent of its energy consumption by 2020. It has also set a target of making the overall economy 20 percent more energy efficient in 2010 than it was in 2005.

Both targets have been lauded by Greenpeace and other groups but the fact remains that China will continue to remain heavily reliant on coal and other fossil fuels to power its rocketing economy.

Coal still accounts for around 70 percent of China's primary energy consumption, and coal-fired power plants are being built at a rate of more than one a week nationwide.

Experts only a few years ago predicted that China would not overtake the United States as the world's biggest emitter of greenhouse gases for decades.

But amid the frenzied economic growth, that timeframe has been radically brought forward with the International Energy Agency this month forecasting that China would overtake the United States this year.

Yang Fuqiang, head of the Beijing branch of the US-based China Sustainable Energy Programme, said although China was taking measures to reduce its consumption of fossil fuels, it needed do more.

Tax incentives for enterprises to adopt energy-saving practices, prohibiting financial institutions from funding polluting projects and gradually raising fossil fuel prices were all key, he said.

But even if tougher policies are introduced, implementation is a big problem as provincial and local authorities in China are famously disobedient of the central government if orders from Beijing do not suit their interests.

China's efforts to curb its greenhouse gas emissions will be In focus when the United Nations Framework Convention on Climate Change conference begins in Bali next week.

The conference aims to launch a roadmap for negotiating cuts in countries' carbon emissions from 2012, when current pledges under the Kyoto Protocol expire.

As a developing nation, China, is not obliged to cut its greenhouse gas emissions under the existing procotol and has given no signs that it will bow to pressure and agree to some binding targets for the post-2012 era.

"China's position is not going to change," Yang said.

In his most recent comments on the issue, Chinese Premier Wen Jiabao said last week in Singapore that China would aim to cut back annual emissions over the next five years back to 2005 levels.

However he also acknowledged that China was already falling behind in its goals to cut pollution levels and improve energy efficiency.

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