Pumping carbon dioxide underground on a massive scale has been talked about for years; the idea is to "sequester" the greenhouse gas so that it won't enter the atmosphere and contribute to global warming and climate change.

Technology Review asked Howard Herzog, an MIT chemical engineer and program manager of the Carbon Sequestration Initiative, an industrial consortium, for his take on the subject.

His appraisal of the state of sequestration: first, the geological questions are being resolved favorably; second, without policies that put a price on carbon, it is unlikely that more sequestration facilities will actually get built.

The United States is the world's leading carbon dioxide emitter, but the Bush administration opposes regulating carbon dioxide. Herzog says he expects the technology case for carbon sequestration to be further solidified in the next few years, in time for the next administration in Washington to take action.

Technology Review: Why has interest in this field grown so rapidly?

Howard Herzog: When you look at the possible ways to reduce carbon dioxide emissions, there are only a handful of ways you can go: non-carbon energy, improved efficiency, and then of course if you continue using fossil fuels -- which it looks like we will -- to capture and store the carbon dioxide.

TR: Norway was the first country to enact a CO₂ tax, in 1991. How has that played out?

HH: It sent a signal to see if there was a way to reduce CO₂ emissions and resulted in a large project in the North Sea to sequester carbon dioxide from a natural-gas field.

TR: What do we know about its performance?

HH: There is no indication of any leaks, and they've done some seismic tests that show the CO₂ is staying in the underground geological formation. The amount of monitoring hasn't been such that you can say for certain there are no leaks -- but none has been detected.

TR: What about the question of geologic suitability generally -- what do we know about the risk of carbon dioxide leaking out?

HH: The reducing of uncertainly with geological storage has come a long way in the last couple of years. I think the work coming out says [researchers] are gaining a higher degree of confidence that this will work -- and work well, if implemented with good practices. We are moving down the road toward understanding what those good practices are. And I think over the next couple of years we are going to see a lot more pilot tests happening.

TR: What else is emerging on the policy front?

HH: With a European carbon-trading system, several utilities have announced projects to build plants with CCS [carbon capture and storage], which is indicating that those price signals were enough to induce serious interest. Outside of Europe, despite the lack of specific policies, there is still a lot of interest in this technology. People feel that over the next 10 years, policies will be put in place throughout most of the developed world.

SAMPLING OF LARGE-SCALE PROPOSED PROJECTS TO CAPTURE CO2