Could the answer to global warming actually lie in putting more chemicals into the atmosphere? A growing number of climatologists and engineers believe that "geoengineering" — putting reflective aerosols into the atmosphere — may be the most cost-effective way of reversing global climate change.
In a study released earlier this week, California Institute of Technology scientists say that "solar radiation management" — essentially "turning down the sun" by artificially reflecting some of the sun's rays back into space — could be used to change the climate back to "pre-industrial" levels. According to the report, by reducing the sun's rays just .5 percent, the entire Arctic sea ice extent could be recovered.
In fact, geoengineering has already happened in a sense. In 1991, Mt. Pinatubo, a volcano in the Philippines, had one of the strongest eruptions recorded in the 20th century. The resulting explosion injected 20 million tons of sulfur dioxide into the stratosphere, resulting in as much as a 4 percent decline in total solar radiation that reached the earth during the first half of 1992. The global temperatures during the following months were about a degree cooler than normal.
"We know for a fact that geoengineering would cool the planet just by virtue of watching what happened after the Pinatubo eruption. But it would also have other consequences" study coauthor Doug MacMartin says. "It's clearly not as good as cutting emissions in the first place, but given the trajectory we seem to find ourselves on, it might be the only option."
Of course, messing with the chemistry of earth's atmosphere is risky business. Most previous attempts at modeling geoengineering have considered injecting aerosols uniformly across the entire stratosphere — which means the earth's climate would ultimately be impacted in unpredictable ways. Putting more chemicals into the stratosphere could also open new holes in the ozone layer, scientists warn. It could also cause unpredictable changes to earth's precipitation patterns.
During the Cold War, the United States looked into using the weather as a weapon and the Soviet Union looked for ways to make Siberia more hospitable, though neither experiment succeeded. In 2009, in one of the first ever field tests to use geoengineering as a climate change solution, a Russian scientist and Vladimir Putin adviser put aerosol generators on top of a helicopter in order to measure the resulting decrease in the sun's rays.
In his latest proposals, MacMartin says that by targeting specific parts of the atmosphere — say the northern hemisphere, for instance, effects to the rest of the earth would be minimized. Stratospheric aerosols would likely be delivered via aircraft that flew higher than standard commercial planes.
Scientists could theoretically control how long the aerosols stayed in the atmosphere depending on how high in the atmosphere they were released.
"Our question is — can we do this in a way that doesn't solve all the problems, but at least mitigates some of them," MacMartin says.
That means starting small. Ideally, MacMartin says, aerosols could be injected into the Northern Hemisphere during the Arctic summer and they would naturally dissipate within a few months.
"We don't know what the consequences would be of doing this, but we also don't know what the consequences of not doing this would be," he says. "It seems to me to be quite likely we will find ourselves in a place where the consequences of not doing geoengineering are so insurmountable we'll feel forced into a position of doing at least some of it."