Turning down the sun

If you can’t stand the heat, turn down the lights.

Canadian researcher David Keith has an idea that might help reduce global temperatures in case of a climatic disaster like rapidly melting polar ice caps: suspending billions of dust-sized particles in the upper atmosphere to reflect light and prevent it from warming the earth.

No one advocates the deployment of such an untested scheme. But Keith’s idea is the latest in a growing list of proposals to try to change — or geoengineer — the earth’s climate on a large scale in case of looming disaster. It has ratcheted up debate over whether governments should research geoengineering solutions and whether even doing such research is a dangerous distraction from the ultimate goal of reducing emissions.

Meanwhile, Keith has begun to examine the feasibility of such an idea. “Knowing that we might be able to use particles like these to block out light has enormous value, the same way as having a fire extinguisher in the house is a good idea,” said Keith, who proposed the idea in a study published in October 2010 in the Proceedings of the National Academy of Sciences. “But no sensible person thinks we should do this before we know a lot more about the risks, or do this instead of cutting emissions.”

The idea of putting particles into the atmosphere to cool the globe isn’t new, but most studies into the subject have focused on the impact of naturally occurring sulfur aerosols from volcanic eruptions. The 1991 eruption of Mount Pinatubo in the Philippines, for example, spewed 20 million tons of sulfur dioxide into the air, which spread in a haze throughout the Earth, reflecting sunlight back into space. Average global temperatures decreased by about 0.9 degrees Fahrenheit over the next 18 months, according to Keith.

Volcanoes loft sulfur dioxide particles about 20 miles up into the stratosphere, where they mix with water vapor and reflect some sunlight back into space. However, these acidic droplets also help break down ozone into regular oxygen gas. That’s a problem because ozone blocks harmful ultraviolet radiation.

Keith’s hypothetical particles would avoid this thorny problem by being designed to levitate about 35 miles above Earth, well above the stratosphere. They also could be engineered to drift toward the Arctic or Antarctic, which could prevent a catastrophic loss of ice caps and glaciers, Keith said. Aligning the particles at the poles would also help preserve normal levels of light reaching the temperate zone surrounding the equator. Light levels in temperate and tropical areas are important to the vitality of plant life, which absorbs carbon, and provides the basis for food chains around the world.

“It’s a really neat idea, subtle and ingenious, that definitely merits further study,” said Jon Shepherd, a climate researcher at the University of Southhampton in the United Kingdom uninvolved in the study. “It’s anybody’s guess whether it’ll prove to be feasible in practice, but well worth exploring.”

But not everybody is thrilled about the idea. “We shouldn’t be putting nanoparticles in the atmosphere, because what goes up must come down,” said Diana Bronson, a spokesperson for the ETC group, an international environmental advocacy group opposed to large-scale geoengineering research. “Eventually these things will drift down to Earth, and that’s concerning because the toxicological properties of nanoparticles are not well understood.”

Keith emphasizes that his ideas, like most in the field, are preliminary, and further improvements are almost certain to occur in the future. Furthermore, he thinks it might be possible to design particles to corrode into the equivalent of dust, which would represent a small fraction of the dust that already exists in great quantities in the lower atmosphere.

Perhaps the most compelling argument against research in geoengineering is the idea that it presents a moral hazard: If people think there may be technological means of reducing some negative effects of climate change, they may be less likely to support the kinds of cuts in carbon emissions that most climate scientists agree are vital.

“This is the serious issue — that just having [geoengineering research] on the table will encourage people to do less,” Keith said. “That’s somewhere Diana Bronson and I would totally agree.”

But it’s hard to know what the effect of research will be, and many contend it is pointless to try to stop it. In conjunction with the Royal Society, which advises the British government on scientific matters, Shepherd published a 2009 study assessing a range of geoengineering options and public attitude toward them. Shepherd said that when many people learned about the existence of geoengineering proposals – like reflecting sunlight with mirrors deployed in space – they reported being more likely to  pursue habits that contribute to less carbon emissions than before.

Under pressure from environmental groups such as ETC, the United Nations Convention on Biological Diversity took up the issue at its biannual meeting in Nagoya, Japan in October 2010. The convention, which includes 193 countries but not the United States, approved an informal “moratorium” on real-world geoengineering activities until threats to biodiversity are better understood.

“It’s a strong expression by the international community — minus the United States, Andorra and the Holy See — that we must proceed with caution and look at effects on biodiversity before experimenting on the real world,” said Bronson.

Other environmental groups see it somewhat differently. Scientists from the National Resources Defense Council and Environmental Defense, for example, have joined a geoengineering task force set up by the non-partisan National Commission on Energy Policy, which seeks to bring scientists, environmentalists and policymakers together to consider the ethics and civics of this research.

“I think the U.N.’s statement was unfortunate,” said Sasha Mackler, the commission’s research director. “It’s premature to bring geoengineering into these sort of frameworks because it’s such a small, nascent field.”

With several countries moving ahead on setting up research programs, “If any group or [any] country ever decides to engage in geoengineering we should have the tools, science and information to understand what the implications of their actions could be, and how we might address them,” Mackler said.