Few scientists working on ways to geoengineer the atmosphere to cool Earth think it鈥檚 anything but a scary idea. Unfortunately, it鈥檚 a scary idea that we may soon need to embrace.
Solar radiation management (SRM) attempts to slow the more disastrous aspects of rising global temperatures by adding particles to the upper atmosphere to reflect a small percentage of incoming sunlight, potentially slowing, halting or even reversing warming.
Researchers at Harvard University are about to launch a project to field test the idea and see if it could work for real. It will be on a far smaller scale than necessary to alter planetary temperatures, but it still amounts to the world鈥檚 biggest trial of the technique. The plan is to spray chemicals such as calcium carbonate into the stratosphere from a balloon above Arizona.
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Those who study geoengineering take great pains to emphasise that this method, potentially quick to deploy and relatively cheap, would not be a permanent fix for global warming. It would be, in effect, a climate tourniquet to temporarily stem the upward march of temperatures and the dangers that flow from that.
A dangerous idea
SRM alone would do nothing to halt the rise in atmospheric CO2, nor would it halt the growing acidification of the oceans. It also brings risks: the possible environmental side effects include massive droughts and disrupted rainfall patterns, while the political conflicts over control and liability may prove equally or even more dangerous.
But despite all these shortcomings, we may eventually have to use it. Why? Because efforts to reduce greenhouse gas emissions planetwide have been sluggish, all but wiping out the chance of holding global temperatures to a 1.5掳C increase, below which seriously damaging climate change is thought unlikely.
Even avoiding a 2掳C rise now looks in doubt. And there is widespread agreement among climate scientists that warming above 3掳C risks 鈥渃atastrophic鈥� and 鈥渁pocalyptic鈥� impacts.
Such delay brings one major complication to the fore: the lag between action and effect. Due to various geophysical factors, such as CO2 persisting in the atmosphere for decades, even a rapid reduction in greenhouse gas emissions won鈥檛 immediately end temperature rises. The longer we wait to really get going, the more likely it is that we鈥檒l see more than 3掳C of warming, even after our efforts have begun in earnest.
Political fallout
At the planetary level, that would mean that our best efforts may not be enough to keep temperatures at a liveable level. Politically, that means billions of people and many countries will have drastically changed their lifestyles and economies without any apparent benefit. Imagine the political fallout when we eliminate carbon emissions but temperatures keep rising and climate disruption worsens.
Thus the importance of the , and those to follow, for a stopgap technique that could help avoid such fallout. Complex computer simulations show that SRM could hold down temperatures and real-world observations of similar natural phenomena (such as volcanic eruptions blasting particles into the stratosphere) support the idea, but there is no hands-on experience with the technique outside labs.
We need to know how it could work and, even more importantly, how it could fail before we face the possibility of needing to use it. Such trials may well prove critical to our civilisation鈥檚 ability to deal with global climate disruption.
Even the co-lead of the Harvard experiment, atmospheric scientist , calls its full-scale deployment a 鈥渢errifying prospect鈥�. He鈥檚 right, but it might be the only way to avoid an even worse outcome.
