Cutting carbon

Cutting carbon emissions would reduce the amounts of greenhouse gases entering the atmosphere. It may also be possible to remove carbon from the atmosphere - by a process known as carbon sequestration.

Carbon could be removed at the point of production - power stations - but no technologies are yet in widespread use. Carbon capture would increase the cost of energy production significantly. And it is not obvious what should be done with the carbon dioxide captured. A favoured route is burying it deep underground.

Researchers are also looking at biological solutions, some of which have a very long history. Long before Europeans arrived, Amazonian Indians were using 'biochar' - plant material turned into a form of charcoal - to fertilise their land. This approach can lock up carbon for many hundreds of years.

Photosynthesis is the key biological process whereby carbon dioxide is removed from the atmosphere. Alongside rainforest preservation, organisms such as marine phytoplankton may offer a route to carbon capture. As iron is often limited in oceans, adding iron could stimulate phytoplankton growth and draw carbon dioxide out of the atmosphere. The wider impact of interfering with ecosystems by such large-scale 'geo-engineering' is unclear, however.

European researchers have recently suggested that photosynthetic bacteria in the oceans could be another carbon sink. The genome sequence of Polaribacter revealed genes for a light-sensitive protein, proteorhodopsin, and others suggesting that the microbe may be able to use sunlight to fix carbon into complex organic molecules.

In fact, microbes may play a much greater role in carbon cycling than previously thought, and may therefore help us to manage carbon fluxes. A resurgence of interest in microbiology, driven particularly by genome sequencing, is highlighting immense diversity in bacteria and archaea (single-celled life forms similar to bacteria but more closely related to eukaryotes). Of particular importance is the ability of some to metabolise methane. In wetlands, the balance of methane users and producers dictates whether sites are net absorbers or emitters of methane.

A better understanding of biological cycling could help improve environmental management and may also identify organisms for use in carbon sequestration.