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Surprising Science

#4: Blot Out the Sun—Or Face Extinction

David Keith, director of the Energy and Environmental Systems Group at the University of Calgary, says geoengineering should be “a central part of how we think about managing climate risk over the next 100 years.”

If we keep emitting carbon into the atmosphere at the current increasing rate, by the end of the century the surface temperature of the Earth will rise between 2.0 and 11.5 degrees Fahrenheit, according to a 2007 report from The Intergovernmental Panel on Climate Change. Depending on the severity of the global temperature increase, the polar ice sheets could melt and disintegrate, causing sea levels to rise, coastal cities to be submerged, and catastrophic storms and other weather-related problems to markedly increase.

Over centuries, says NASA scientist James Hanson, we could actually get a “runaway greenhouse effect, and then that’s it for all the species on this planet.” As the Earth gets warmer and warmer, says Hanson, the oceans will begin to evaporate, creating more greenhouse gas in the form of vapor. Finally, “the oceans will begin to boil, and the planet will become so hot that the ocean ends up in the atmosphere.”

International efforts have been underway for years to cut carbon emissions through conservation and alternative energy—but what will happen if those efforts are too little, too late? A number of climate scientists are now suggesting that we seriously consider proposals to introduce reflective particles or gas into the upper atmosphere to deflect solar energy—simulating the previously measured global-cooling effects of volcanic eruptions.

“There’s no question that … you can put stuff up in the stratosphere and it will cool the planet down,” says David Keith, director of the Energy and Environmental Systems Group at the University of Calgary, who says this kind of geoengineering should be “a central part of how we think about managing climate risk over the next 100 years.”

“The most obvious thing to do is put reflective aerosols into the air because that’s roughly what nature does with volcanoes,” says Keith. “After a big volcano [eruption] like Pinatubo, the earth gets colder within a year and we know a fair amount about what happens.” When Mount Pinatubo erupted in 1991 in the Philippines, the average global temperature temporarily decreased by nearly one degree Fahrenheit as particles hung in the stratosphere.

Some models propose pumping sulfur dioxide gas into the stratosphere through long tubes.  One such model has been put forth by Intellectual Ventures, a company founded by former Microsoft technology chief Nathan Myhrvold, who suggests we might pump sulfur dioxide through “a hose lifted more than 15 miles into the atmosphere using helium-filled balloons.”  Other studies have indicated that it may be better to directly release sulfuric acid or engineered nanoparticles from high-flying aircraft.

Keith thinks that there should be a serious international research program that looks at this type of technology, and “if the results are that it appears this can meaningfully reduce climate risks, then we should … begin to implement gradually.”


How effective could this be? Nobel Prize-winning atmospheric chemist Paul Crutzen, who has put forth proposals for this kind of geoengineering, says “About 3 million tons per year of sulfur are needed to lower average temperature at the Earth’s surface by a couple of degrees [Celsius].” Or around 4 degrees Fahrenheit.

According to researchers at Rutgers University, “Anthropogenic stratospheric aerosol injection would cool the planet, stop the melting of sea ice and land-based glaciers, slow sea level rise, and increase the terrestrial carbon sink, but produce regional drought, ozone depletion, less sunlight for solar power, and make skies less blue.”

Why We Should Reject This

There is no question that geoengineering will have a number of negative consequences—including many we probably haven’t even considered.

“You’re altering the natural system … to lower the temperature,” says Bill Chameides, dean of Duke’s Nicholas School of the Environment. “But while you’re lowering the temperature by reflecting light from the stratosphere, you’re decreasing the amount of light that’s absorbed in the stratosphere, that’s absorbed in the atmosphere, that’s absorbed in the surface of the earth.  As a result of that you’re going to change the atmospheric circulation. As a result of that you’re probably going to change precipitation patterns. and as a result of that who knows what? And so what you’re doing is maybe solving one problem and creating another that is maybe even worse than the first one.”

“Ozone would be a problem,” says Crutzen. “[Geoengineering] delays the ‘repair’ of the ozone hole over Antarctica by several decades.” This would expose the Southern Hemisphere to dangerous ultraviolet rays, and, in effect, to increased rates of skin cancer. Other side effects could include increased acid rain, acidification of the oceans, and changes in rainfall that would cause flooding and droughts.

There is also the possibility that different countries could have different views on where their thermostat should be set, leading to war, says Keith: “These are technologies that have a lot of similarities to nuclear weapons in terms of their leverage and control over nature. And in a world with nation-states that’s a scary thing.”

More Resources

Summary of geoengineering research by David Keith.

Intergovernmental Panel on Climate Change Web site.

Intellectual Ventures homepage.


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