"While reducing emissions is crucial, no level of reduction undertaken now can reverse the warming effect of past and present greenhouse gas emissions."
A Past Resort
Humanity is so desperate for solutions to combat climate change that even methods once touted as speculative science fiction are now being entertained as a plausible way forward.
Solar geoengineering, or solar radiation modification (SRM) — the process of cooling the planet by reflecting sunlight, likely by injecting aerosols into the atmosphere — is one such proposal.
The scientists are not, however, advocating solar geoengineering as the end-all solution, or even a solution. Reducing greenhouse gas emissions is still a must, they caution, no matter what — but they stress the need to properly understand all the benefits and drawbacks of sunlight blocking before it can be completely discounted.
"Given the severity of climate change," the letter begins, "scientists and scientific bodies have recommended research on potential approaches to [SRM]... to slow climate warming and reduce climate impacts."
The letter accounts for several approaches to solar geoengineering. The first and most well-understood is stratospheric aerosol injection, which would reduce sunlight by releasing aerosols like sulfur dioxide into the atmosphere.
Another method, known as marine cloud brightening, would seek to turn clouds into giant sun reflectors by adding sea salt aerosols that would increase their brightness, and a similar method called cirrus cloud thinning would diminish the titular clouds to reduce the amount of warming infrared light they retain.
Positing that decisions on whether to use these methods will be made in the next 10 to 20 years, the scientists call for widespread and extensive research programs, comprehensive assessments on how SRM would affect the environment both globally and regionally, and cooperative international decision-making. After all, they argue, those choices would likely affect the entire planet.
Even though the 2015 Paris Agreement aims to keep warming below 1.5 degrees Celsius "tipping point," the scientists maintain that threshold will be surpassed "in the near term," even with "aggressive action" to reduce emissions.
There is simply too great a number of greenhouse gasses like CO2 already in the atmosphere, they say, and the gasses' long shelf life means their quantity won't significantly reduce anytime soon.
"While reducing emissions is crucial, no level of reduction undertaken now can reverse the warming effect of past and present greenhouse gas emissions," the scientists wrote.
Conversely, what makes solar geoengineering such an attractive option is how quickly it could reduce warming. In fact, pollution from aerosols is already helping to keep the climate cool and "are currently estimated to be offsetting about a third of greenhouse gas climate warming."
All that being said, the call for researching solar geoengineering should not be used to downplay the horrid ways it could backfire. But at some point, we may have to ask ourselves: do we risk it?
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