By Cornelia Dean

(Credit: Reuters/NASA)  

From our colleagues at Dot Earth:

Some questions are relatively straightforward. For example: Could engineers pump chemicals into the atmosphere to increase the amount of sunlight reflected away from Earth, cooling the planet? Almost certainly, the answer will turn out to be yes.

But would the consequences of this step or any other climate-altering geoengineering be acceptable? From an engineering standpoint, that question is hard to answer – no one can say for sure what the consequences might be. Beyond that, though, what is “acceptable?” This is not a question that scientists or engineers have the authority to answer.

Although geoengineering is a subject of lively debate among a relatively small group of scientists, so far there has been little public discussion. (I wrote an article about the technology, and another one about engineering ethics generally.) Now the Royal Society, Britain’s leading scientific academy, has entered the debate with a new report, “Geoengineering the Climate.”

At the moment, the technology of geoengineering “is bedeviled by much doubt and confusion,” the astrophysicist Martin Rees, who heads the Royal Society, writes in the report’s introduction. “Some schemes are manifestly far-fetched, others are more credible, and are being investigated by reputable scientists; some are being promoted over-optimistically.”

The report, by a panel of experts convened by the society, says more research is needed on geoengineering techniques, and that it should involve international collaborations and discussions with the public.

The best approach – the “safest and most predictable,” the report says – would be to avoid the need for geoengineering in the first place by drastically reducing emissions of heat-trapping greenhouse gases. But unless emissions are cut to half of what they were in 1990, the report says, the planet appears to be on course for a rise in temperature of almost 4 degrees Fahrenheit by the end of the century – enough to cause severe problems and, potentially, to prompt calls for geoengineering action.

But as Dr. Rees put it, “the technology do to so is barely formed, and there are major uncertainties regarding its effectiveness, costs and environmental impacts.” Because there is so little peer-reviewed research, he wrote, the report as a whole is based on “necessarily preliminary and incomplete information.”

The other questions are more difficult. For example, using chemicals to make the planet more reflective might cool things a bit, but it would do nothing to reduce other greenhouse-gas impacts, like rising acidity in the oceans as they absorb more carbon dioxide.

Is that acceptable? Who decides?

As people look to geoengineering as a weapon against the effects of global warming, the report says, public attitudes toward geoengineering “and public engagement in the development of individual methods proposed, will have a critical bearing on its future.”