In a lab at Harvard, researchers are trying to replicate the conditions of the stratosphere-the part of the atmosphere that stretches roughly six to 31 miles above the surface of the planet-in tubes. Their goal: to better understand what might happen if humanity eventually decides to embark on a radical, controversial plan to temporarily cool the planet by spraying clouds of particles into the sky.
If it ever happens, the process might involve sending planes into the sky to release particles of a compound like sulfur dioxide that can reflect some sunlight back into space and could temporarily cool the planet. It's not a fix for climate change, and it's a form of geoengineering so extreme that it carries risks that may not be fully predictable.
"Our team here is doing research, because we believe there is still a lot of uncertainty around solar geoengineering, and we think that there is a chance for potential benefits around the world, "says Elizabeth Burns, managing director of Harvard's Solar Geoengineering Research Program. "But we also think that there is a chance for a very real risk."
In a new study in Nature Climate Change researchers from Harvard, MIT, and Princeton used a state-of-the-art, detailed computer model to look at what might happen if solar geoengineering was used to reduce global temperature increases in half. In the scenario, they found that reducing the warming would also offset the increasing intensity of the hurricanes and would help to moderate extreme rain and lack of water for farming (in the model, the rain decreased, but also did the evaporation). Less than 0.5% of the world might see increased impacts from climate change. This is in contrast to some previous studies that found that this type of geoengineering could benefit some parts of the world while large other areas were damaged.
The concept of spraying chemicals in the sky to cool the Earth is not new. It's the same process that happens naturally when the volcanoes erupt. In 1991, when Mount Pinatubo erupted and spilled millions of tons of sulfur dioxide into the atmosphere, it cooled the planet by half a degree Celsius for more than a year. But it's only recently that the researchers have begun to seriously study what might happen if humans deliberately do something similar. At this point, it's still a very small area of study, with relatively little funding, and many unknowns.
Burns emphasizes repeatedly that the world's priority should be to reduce emissions to zero. "Solar geoengineering can not be a substitute for reducing emissions, because it does not address the root cause of climate change," she says. "So if we are to achieve a stable climate, we really need to reduce emissions to zero and then eventually remove the carbon dioxide that is in the atmosphere and store it underground or elsewhere. These actions are really addressing the root cause. Solar geoengineering does not. "
" Alan Robock, a professor of environmental sciences at Princeton, says, "Solar geoengineering does not."
"It would only potentially be used temporarily while we rapidly reduce our emissions to the atmosphere and figure out cheap ways to separate carbon dioxide out," says Alan Robock, "So nobody talks about doing it instead of mitigation. "Robock has documented 27 potential risks of the idea, from the possibility of ozone depletion to potential dryness and a reduction in solar energy production. The paper lists only six potential benefits, but one is significant: the reduction in surface air temperatures could "reduce or reverse the negative impacts of global warming, including flooding, drying, stronger winds, ice-leaching, and sea level rise."  At Harvard, the researchers are studying the possibility of using calcium carbonate (the same particle found in chalk or toothpaste) rather than sulfur dioxide; While sulfur dioxide can speed up the destruction of the ozone layer, calcium carbonate could potentially help it and avoid some other risks. Although the team is now the first to do a real-world experiment, which involves launching a balloon into the stratosphere, releasing a small amount of calcium carbonate, and then measure how the light scatters and changes in atmospheric chemistry. The team was interested in conducting the experiment this year, but will not move forward without the recommendation of an external, independent advisory committee that it creates. "For us, the management of this is equally important as the scientific goals of the experiment," says Burns.
One of the fundamental questions of solar geoengineering is who can decide if it happens: For a action that affects the whole planet who has that right? The actual process may be inexpensive enough (by one estimate, less than $ 10 billion a year) that there is a risk that a single country could decide to act on a one-to-one basis. That's part of the reason that research is so critical; the world needs to understand more about what could happen and whether it could happen responsibly.
"If the international community is faced with impacts of climate change that are severe or more severe than expected, when people then talk about available tools, we need a better understanding of what solar geoengineering may or may not be able to do, "says Burns. "In our view, it's not saying that we need it. If anything, I hope we do not need it. It's a very scary technology. It's pretty terrifying. But the world with severe climate change impacts can also be very scary. And so I think we're researching it so that we can better understand the potential benefits as well as the potential risks that would come alongside this technology. "