"Our climate model simulations suggest that if we produce a world with a lot of greenhouse gases in the atmosphere, even relatively crude climate engineering could bring the climate closer to how it was before those greenhouse gas emissions," Caldeira told environmentalresearchweb. "It would not be perfect, but it would be pretty good."

We now know that the Earth is warming rapidly. Arctic sea ice is disappearing at a faster rate than ever before and the southern part of the Greenland ice sheet may collapse at any time. What’s more, the oceans are becoming more acidic and coral reefs and other sensitive marine organisms look set to suffer.

In an ideal world we would reduce carbon dioxide emissions to combat greenhouse gas warming. But, in reality this may be difficult as many nations, especially emerging ones, are reluctant to reduce their emissions for fear of harming their economy. "Much of the developing world is looking to China and India, who have chosen coal power as their main source of energy, as a model, while those of us in the developed world are looking for ways to kick-start our fossil-fuel economies," explained Caldeira.

Climate engineering is thus an alternative, albeit controversial, solution.

Caldeira and Wood came to their conclusion by performing several computer simulations with carbon dioxide added to a model atmosphere. The researchers repeated their simulations, which are based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model v3.1, with and without reduction in the amount of sunlight reaching the Earth's atmosphere. They found that when absorbed sunlight was reduced, the high-carbon dioxide simulation results resembled the low-carbon dioxide simulations without climate engineering.

The duo describe several ways to reduce the amount of solar radiation falling on Earth, but the simplest approach would be to place dust in the stratosphere that would reflect this radiation back into space. "The easiest way to do this may be to introduce sulphur dioxide gas and let it oxidize to sulphate particles," explained Caldeira.

Caldeira and Wood say that a climate engineering programme could help reduce the risk of catastrophic climate change. "But the more difficult question is how society and politicians will respond to such measures," added Caldeira.

The scientists say they now plan to investigate how controllable climate may actually be. For example, what would we need to do in concrete terms if we wanted to produce a particular climate state?

We need climate engineering research and development plans, declares Caldeira, because it is looking increasing unlikely that greenhouse gas emissions will decrease &nsash; at least in the foreseeable future.

"Perhaps we might depend on the human capacity for self-sacrifice when faced with unprecedented, shared long-term risk, and therefore could happily rely on future reductions in greenhouse gas emissions," he said. "But if not, we'd better have another plan."

The researchers reported their work in Phil. Trans. R. Soc. A.