New technologies that remove carbon from the atmosphere could be needed to combat man-made climate change, according to a report published today by the Royal Society.

Most attempts to deal with climate change involve reducing emissions of carbon dioxide – the report also calls for governments to work towards an agreement to cut carbon dioxide emission by 50% on 1990 levels by 2050 – but some scientists believe that this may not be enough to stop the planet's average temperature rising by 2 °C by the end of the century.

Geoengineering is the deliberate intervention into the climate system to counteract man-made global warming. It could offer a solution to climate change, but some scientists are reluctant to discuss it, fearing that it could encourage complacency in cutting emissions.

Giant sunshades

The Royal Society report, Geoengineering the climate: Science, governance and uncertainty, looks at different geoengineering options for tackling climate change, including constructing giant sunshades in space that can reflect the Sun's rays and introducing iron into the world’s oceans to rapidly increase the amount of phytoplankton that consume carbon dioxide.

The 12 authors of the report – led by John Shepherd from the UK’s University of Southampton – divide geoengineering into two types: carbon dioxide removal (CDR) that acts to removes carbon dioxide from the atmosphere and solar radiation management (SRM), which involves reflecting sunlight back into space.

Soaking up carbon

They conclude that CDR technologies would be best suited to combat climate change. These include capturing carbon dioxide from ambient air as well as using land to soak up carbon. "It is too soon to pick winners," says Shepherd. "We need more research into several avenues to decide which technologies are most effective."

However, they conclude that SRM methods, such as constructing giant sunshades in space and pumping aerosols into the atmosphere to reflect sunlight, would not be long-term solutions and their usage offers potentially dangerous consequences. "Using aerosols would be like taking an aspirin to cure a headache," Shepherd told "But it might not be a long-term solution to the underlying problem."

The report, which contains seven recommendations, calls for £10m per year to be spent by UK research councils to fund geoengineering projects. "This is still only about 10% of what the UK spends on climate change," says Shepherd. "We must make sure that the projects are researched in a responsible manner and that they are openly discussed."

For a detailed discussion of geoengineering schemes, see "Engineering the climate", which appears in the September issue of Physics World.