But experts said Friday that large-scale production remains many years away, and if not done properly could flood the atmosphere with climate-changing greenhouse gases.
Frozen mix of water, gas
Combustible ice is a frozen mixture of water and concentrated natural gas. Technically known as methane hydrate, it can be lit on fire in its frozen state and is believed to comprise one of the world's most abundant fossil fuels.
The official Chinese news agency Xinhua reported that the fuel was successfully mined from beneath the South China Sea on Thursday. Chinese Minister of Land and Resources Jiang Daming declared the event a breakthrough moment heralding a potential "global energy revolution."
A drilling crew in Japan reported a similar successful operation two weeks earlier, on May 4 along the Shima Peninsula.
For Japan, methane hydrate offers the chance to reduce its heavy reliance on imported fuels. In China, it could serve as a cleaner substitute for coal-burning power plants and steel factories that have polluted much of the country with lung-damaging smog.
Estimated reserves are large
Methane hydrate has been found beneath seafloors and buried inside Arctic permafrost and beneath Antarctic ice.
Estimates of worldwide reserves range from 280 trillion cubic meters (10,000 trillion cubic feet) up to 2,800 trillion cubic meters (100,000 trillion cubic feet), according to the U.S. Energy Information Administration. By comparison, total worldwide production of natural gas was 3.5 billion cubic meters (124 billion cubic feet) in 2015, the most recent year available.
That means methane hydrate reserves could meet global gas demands for 80 to 800 years at current consumption rates.
Yet efforts to successfully extract the fuel at a profit have eluded private and state-owned energy companies for decades. That's in part because of the cost of extraction techniques, which involve large amounts of water and power to flood methane hydrate reserves so the fuel can be released and brought to the surface.
There are also environmental concerns, said David Sandalow, a former senior official with the U.S. State Department now at Columbia University's Center on Global Energy Policy.
If methane hydrate leaks during the extraction process, it can increase greenhouse gas emissions. If it can be used without leaking, it has the potential to replace dirtier coal in the power sector.
"The climate implications of producing natural gas hydrates are complicated.There are potential benefits, but substantial risks," Sandalow said.