Sir

Neil Wilson is concerned about technologies that accelerate a net release of fossil carbon to the atmosphere, as he says in his Correspondence (Nature 451, 768; doi:10.1038/451768e 2008) about our Letter (Nature 451, 176–180; 2008). My co-authors and I share his concern. Fossil fuels will supply society at some level for at least another half-century, given current economic imperatives, although clean-energy cycles that involve zero-carbon emission will ultimately be nuclear in nature, with fusion in the form of solar energy and fission in the form of geothermal energy.

It is therefore crucial to clean up the fossil-fuel industry quickly and economically. Carbon capture and storage are, in theory, deployable. In practice, these are hindered by the enormous number of effective retrofitted storage projects that are needed, and by economic models that allow fossil-energy recovery processes based on existing technologies to be very profitable.

Our Letter is about deep subsurface biodegradation of crude oil and the nature of the deep subsurface biosphere. It raises the possibility that acceleration of this process could provide methane, or even hydrogen, from spent oilfields or as an alternative energy vector for heavy-oil energy recovery. Although this approach remains speculative, it could provide natural gas or hydrogen with low energy and water input, instead of environmentally expensive heavy oil.

Methane and hydrogen are preferable to coal and heavy oil as fuels. The technology — if feasible — could be introduced by the oil industry without major changes in infrastructure or work practices.

This attempt to clean up the final phase of the fossil-fuel industry quickly is one justification for our work at a time when everyone would prefer clean, zero-carbon emission energy to be readily available. Changes in human imperatives call for bold decisions by shareholders, voters and legislators to force rapid and convincing changes in the energy industry.