Biden Gives the Go-Ahead on Researching Ways to Reflect the Sun’s Rays
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The most promising way to offset climate change’s effects could be injecting sulfur dioxide (SO2) aerosols directly into Earth’s stratosphere.
However, even current tanker planes would have to be modified to reach the required heights to spew these aerosols.
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There is no “one size fits all” solution to climate change. While decarbonization remains the most important tool in our mitigation toolbox, humanity will need all the help it can get to offset the most devastating effects of our rapidly warming world. One of those tools could be an idea called solar geoengineering (and no, we’re not talking about Dyson spheres). Instead, this kind of geoengineering aims to make Earth’s atmosphere a more effective solar reflector—and now the White House wants to take a closer look.
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Last month, the White House Office of Science and Technology Policy announced a five-year study to scientifically assess “solar and other rapid climate interventions in the context of near-term climate risks and hazards.” In other words, can we somehow alter our atmosphere so that it cools the planet and offsets climate change’s life-threatening side effects?
A Technique as Old as Time
A couple ideas have been floated on ways humans could alter the skies above them. One, called “marine cloud brightening” would spray sea salt crystals into the low-lying clouds covering the oceans. Another idea requires thinning cirrus clouds so heat could more easily escape Earth’s surface. But the most promising (and also the most controversial) plan is to inject sulfur dioxide (SO2) aerosols directly into Earth’s stratosphere.
This particular cooling strategy has been around for about 4.6 billion years. Throughout Earth’s geologic history, volcanoes spewing sulfur dioxide (SO2) have temporarily cooled the planet as the spreading gas diffuses light, turning the sky white and, by extension, making it reflective. For example, the 1991 Mount Pinatubo eruption in the Philippines temporarily cooled Earth’s surface 1 degree Fahrenheit while boosting photosynthesis due to increased diffused light (AKA the stuff plants crave), which in turn pulled more carbon from the atmosphere.
In 1965, a report by the U.S. Environmental Pollution Panel suggested that humans could purposely inject reflective aerosols in the atmosphere to mitigate the worst outcomes of a warming climate. At the time, the paper estimated that such a bold plan could cost $500 million a year. Today, that figure is more like $10 billion. But a cooler world could stave off some of climate change’s worst effects—scientists think the estimated 2 degrees Celsius drop could even refreeze Earth’s poles and slow sea level rise.
Despite all these positives, there’s one really big negative: sulfur dioxide is toxic. In fact, the most common source of the gas today comes from power plants. The gas has also been linked to acid rain and respiratory illness.
“Yes, damaging the ozone is bad, acid deposition is bad, respiratory illness is bad, absolutely. And spraying sulfur in the stratosphere would contribute in the bad direction to all of those effects,” Edward Parson, an environmental law professor at UCLA, told CNBC. “But you also have to ask, how much and relative to what?”
Flying Too High?
The other big roadblock for this ambitious aerosol plan is getting it up in the stratosphere in the first place.
Several studies have shown that the best altitude for deploying aerosols is at about 15 miles above Earth’s surface, where air is calm and the mist could hang around between six months to two years. Unfortunately, only the most advanced high-altitude planes can even hope to reach those heights, which would likely explode costs. Even with some aerosol-spewing plans requiring lower (and less effective) altitudes, current tanker planes, like the Boeing KC-135R or the Boeing KC-46A Pegasus, would have to be modified for the mission. Some researchers even suggest designing an entirely new plane purpose-built to spew some SO2.
Unfortunately, there are other roadblocks that extend beyond altitude. Scientists worry that Earth could effectively lose its blue skies, and the added aerosols could cause a chain reaction of unforeseen consequences. Droughts could intensify in sub-Saharan Africa, weakened extratropical storms could exacerbate pollution, and diseases like malaria could get even worse.
As part of the spending budget for 2022, this five-year study will hopefully find some answers to these lingering questions and figure out once and for all if solar geoengineering is really a helpful ally in the fight against climate change, or an ecological risk whose costs far exceed its benefits.
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