As the world's largest emitters of carbon dioxide -- including Japan -- struggle to find quick and effective ways of cutting emissions to curb global warming, projects to store the gas underground are attracting public attention.

Research and development of technology to capture and isolate carbon dioxide started in the early 1990s in Japan. But field tests in Nagaoka, Niigata Prefecture, that were started in July have fueled new hopes that the technology may be a breakthrough in efforts to combat climate change, yet still enable the country to meet its energy needs.

Nagaoka's experiment -- the first project in Japan to store carbon dioxide underground -- is designed to establish technology by 2015 that enables the gas to be captured from large-scale emission sources, such as energy plants, factories and steelworks.

The five-year project, which began in 2000, is being conducted by the Research Institute of Innovative Technology for the Earth (RITE), a Kyoto-based foundation tasked with developing innovative technologies to protect the environment.

RITE was established by contributions from more than 40 companies, mainly in the heavy industry sector, as well as the local and central governments in 1990.

RITE estimates that Japan is capable of storing about 70 billion tons of carbon dioxide underground, including beneath the seabed close to the shore. This total is equivalent to more than 50 times the country's carbon dioxide emissions in fiscal 2001, which totaled 1.3 billion tons, according to the Environment Ministry.

While hopes for the project are mounting and its introduction seems inevitable, some experts and environmental groups are skeptical about whether it is worth the effort to devise technology that will allow researchers in this area to capture and store the greenhouse gas.

"Once established, this method (sequestration of carbon dioxide) has a quicker effect and is more reliable than other possible global warming countermeasures," including the development of technology to shift to renewable energy sources, said project leader Shigeo Murai.

According to a projection for global carbon dioxide levels that takes into account all relevant factors, such as demographic changes and the time frame and cost of other possible countermeasures, Murai emphasized, "it is impossible to reduce gas emissions without resorting to (carbon sequestration technologies)."

After a thorough examination of Japan's strata, the project team chose the Iwanohara natural gas mining base of Teikoku Oil Co. as the experiment site, where 1.1 km below the surface are aquifers covered by a large cap of rock -- an impermeable formation -- so the gas becomes trapped in the aquifers.

The field tests involve injecting 20 tons of liquefied carbon dioxide into aquifers a day until some 10,000 tons have been injected over a period of 18 months. As of December 10, 2,200 tons of gas had been forced into the aquifer since July.

The movement of the carbon dioxide trapped in the aquifers is being monitored through three observation wells to make sure the gas settles and does not leak out.

Murai said the project is designed to keep the annual rate of carbon dioxide leaking from the aquifers below 0.01 percent, so that the gas can be kept underground for nearly 10,000 years.

"The storage technologies are almost at the stage for practical use," Murai said, citing a project in Norway in which 1 million tons of carbon dioxide has been pumped underground a year since 1996 without any problems.

In comparison to other countries, Japan, a country with complex geological strata and frequent earthquakes, has a disadvantage in developing carbon dioxide storage technologies, Murai said. But if engineers are careful in selecting the site, such problems can be overcome, he said.

Murai also acknowledged that reducing the cost of the project is another task. RITE's calculations show that the cost of storing carbon dioxide is around 7,000 yen per ton. In order for Japan to attain the 6 percent reduction target of greenhouse gas emissions under the 1997 Kyoto Protocol, it is estimated that at least 1 million tons of carbon dioxide needs to be stored at one site, Murai said.

This means that currently, it would cost 7 billion yen to store the gas at each site, plus the expenses to continue monitoring the movement of the trapped gas for a long period of time. The cost remains high because the technologies are still at the research and development stage, although the project team plans to reduce the cost by the time the technology goes into practical use.

The Ministry of Economy, Trade and Industry provided 850 million yen in subsidies for the current fiscal year for the 3.9 billion yen project and believes that the storage technologies have a huge potential to curb global warming.

The environmental group Kiko Network, however, has its doubts.

"Since the technologies are not able to isolate carbon dioxide permanently, the techniques are not designed to deal with the root causes of global warming," the nongovernmental organization said in a written statement.

There are concerns about the possibilities of the gas erupting from underground in the event of an earthquake and the technologies are not worth the high cost, the group added.

"It is far better to use the money to reduce the use of fossil fuels and to promote the shift to renewable energy sources," the environmental group commented.

Masaru Hirata, a visiting professor at Shibaura Institute of Technology who specializes in mechanical engineering and energy systems, broadly agrees.

Although he admits that Japan may eventually end up using the carbon capture technologies, Hirata emphasizes that the country should first focus on developing ways to reduce carbon dioxide emissions.

"We should all be reminded that the carbon storage technologies must only be used to gain time for developing other important technologies, such as high energy-efficiency and fuel cell technologies," Hirata said.

Despite the mounting expectations for carbon isolation technologies, he warned that they are merely putting off seeking a solution to the problem and the new knowhow should not be regarded as the solution to climate change.

"If the technologies are instead used as an excuse or a disguise to encourage the use of fossil fuels as before, it means nothing," he said.