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Unless greenhouse-gas emissions drop drastically, efforts to save the planet could depend on controversial technologies that directly manipulate the environment, according to a report by Britain's top science academy.

The study released Tuesday examines geoengineering, a potentially dangerous and unproven branch of climate science that proposes large-scale interference with nature. Examples include sending thousands of gigantic mirrors into space to reflect sunlight away from the Earth, propelling dust or other particles into the stratosphere to mimic the cooling effect of volcanoes and fertilizing the ocean by scattering iron to boost carbon-absorbing plankton.

“The global failure to make sufficient progress on mitigation of climate change is largely due to social and political inertia, and this must be overcome if dangerous climate change is to be avoided,” says the report by the Royal Society. “If this proves not to be possible, geoengineering methods may provide a useful complement to mitigation and adaptation if they can be shown to be safe and cost effective.”

The report arrives ahead of a United Nations conference on climate change in Copenhagen in December, where world leaders will discuss a successor agreement to the Kyoto Protocol, which expires in 2012. The study takes pains to stress that geoengineering technologies are not a panacea for global warming.

Manipulating the environment so aggressively and intentionally is considered irresponsible by some scientists and environmentalists, who both fear geoengineering would give people licence to continue polluting and that it could lead to harmful unintended consequences. For example, using mirrors in space would cause the sun's light to flicker and shooting particles into the upper atmosphere could damage the ozone layer.

The study, called Geoengineering the Climate , recommends increased financial support for research into geoengineering to determine whether effective measures can be developed to slow the Earth's warming.

“It's important to do the research now so that if these ideas really are bad that we know they're bad and in a situation of crisis nobody would decide to deploy them,” said Ken Caldeira, a climate scientist at the Carnegie Institution of Washington. “On the other hand, if they really do … reduce suffering, then it would be a mistake not to take advantage of that opportunity.”

In the worst-case scenarios of climate change, cities such as Vancouver, New York and Shanghai are swamped by rising sea levels caused by melting ice in Greenland and the Antarctic. Other parts of the world could be devastated by extended droughts, hurricanes and other severe weather.

“We have to have some way of managing that risk and geoengineering is the only plausible way,” said David Keith, an expert in the field at the University of Calgary.

Both Prof. Keith and Prof. Caldeira, who were part of the 12-member working group responsible for the report, likened efforts to reduce climate change to preventive behaviour by homeowners, who rid their properties of flammable objects but still purchase fire insurance.

“I look at emissions reductions as trying to keep your house from catching on fire and these geoengineering schemes as a kind of insurance policy,” Prof. Caldeira said.

Prof. Keith said merely talking about geoengineering has been nearly taboo in scientific circles over the past 15 years. However, he said it is “becoming less controversial by the hour” because of increased attention to the seriousness of climate change and reports such as yesterday's.

“The science is very weak and that's exactly why we think research is needed. That's the key point, because of the taboo, there's been so little research on this topic,” he said.

The report notes that global warming will likely exceed 2 degrees Celsius this century unless worldwide greenhouse-gas emissions fall by at least 50 per cent of 1990 levels by 2050, with even greater declines thereafter. Carbon dioxide, which is produced when fossil fuels are burned, and other greenhouse gases trap heat in the atmosphere.