Stratospheric aerosol injection is not a climate solution
Paul Teehan has a PhD in Resource Management and Environmental Studies from the University of British Columbia.
Recent articles in mainstream press (CNN, CBS, Guardian) have discussed the viability of injecting aerosols into the stratosphere in order to dim the sun and potentially cut temperature increases due to global warming in half. The effect would be similar to “mini ice ages” the Earth has experienced in its history following major volcanic eruptions that filled the sky with particulate. It is a tempting solution: it seems to be economically viable at a cost of only a few billions of dollars; it’s technically simple; and it’s likely to actually reduce the global temperature. There are some rather nasty side effects, such as the end of blue skies (the sky would be white), possible excess deaths of tens of thousands per year due to sulphur poisoning, possible disruption of Asian and African monsoon, reduction in efficiency in solar panels, and unknown knock-on effects that are difficult to predict (see this New Yorker article for more). But, with the survival of our ecosystems and humanity itself at stake, surely it’s worth considering? In fact, the history of technological interventions for energy efficiency shows that there is a good chance we would respond to a dimmer sun by maintaining emissions at current levels or maybe even emitting more, which means that dimming the sun would not save us. This is not news to scientists; most are aghast at the thought of geoengineering the planet and would recommend it only as a last-ditch effort to keep us alive a little bit longer. It is not a solution; we have to do it the hard way and cut off emissions at the source.
When people talk about aerosol injection, the framing is usually about whether we can do it, and whether it would have the impact on the climate that we desire. Let’s take those as granted, that we can dim the sun and it would cut global warming impacts due to emissions in half. What happens next? The implicit theory is that humanity gradually reduces our emissions over time, and because the sun is dimmer, we are spared the worse of the climate impacts and our ecosystems survive. Maybe this mitigation buys us some additional time to transition to renewables. A dimmer sun does nothing to reduce other emissions-related impacts like ocean acidification, but maybe we can find other technological solutions to solve these too. This would be a great outcome. Let’s call it the “salvation” outcome. But unfortunately it’s not the only possibility. Here are some others:
“Delay”: With the immediate threat of global warming reduced, the world’s governments feel less urgency to reduce emissions. The transition to renewables slows and emissions plateau. We continue pumping carbon into the atmosphere and now we have to pump sulphur into the atmosphere as well to counter it and this needs to continue indefinitely. Future generations are left with a much harder problem to solve. Meanwhile, the world’s oceans continue to deteriorate. Maybe humanity comes together to solve the problem, and maybe it doesn’t. Our children grow up never seeing a blue sky.
“Rebound”: With the sudden increase in “carbon budget”, some governments feel emboldened to abandon their climate targets and expand fossil fuel extraction and usage. The direct effect of stratospheric aerosol injection is an increase in emissions. Even with the injections, the global temperature continues to climb, though perhaps slightly slower than before, and we may be forced to dim the sun dramatically to keep the temperature down. Eventually we pass a tipping point and ecosystems collapse leading to mass extinction, economic collapse, and the likely end of humanity as we know it.
It’s important to get the framing clear. Don’t mix up the question of whether stratospheric aerosol injection “works” with the question of what are the likely political and social outcomes of this dramatic intervention. It’s an unknown question which of these scenarios, “salvation”, “delay”, or “rebound”, or something else entirely, is most likely, and this is the discussion we should be having.
The history of energy conservation tells us that technological innovations that we expect to result in energy savings tend to be offset by increased consumption, a phenomenon known as the “rebound effect”. The reasoning is straightforward: if something becomes cheaper, people tend to use more of it. For example, LED lightbulbs may use less energy than incandescent bulbs, but the cheaper operating costs mean that more LED lightbulbs will be purchased and installed and used for longer periods of time. Sometimes the expected savings are reduced, and sometimes wiped out completely. In addition, efficiency improvements can stimulate economic growth — cheaper lightbulbs mean more business operating at night, for example — leading to a net increase in energy usage at the macroeconomic level, a phenomenon known as “backfire”, also known as the Jevons Paradox or the Khazzoom-Brooks postulate. The magnitude of the effects are difficult to study and even harder to predict, but they are definitely real.
Would we see a rebound effect in emissions due to the introduction of stratospheric aerosol injection? Considering the difficulty the world’s governments have had making real progress towards emissions targets, and the economic incentives for continuing to extract and burn fossil fuels, it seems highly likely, and more probable than the “salvation” scenario in which we respond to this additional breathing room by emitting less. Frankly, the idea that we are even considering such a drastic approach suggests that we as a society are desperately seeking ways to continue large-scale emissions. If someone is in a growing amount of debt and they open a new credit card, they will probably either maintain or increase their spending, not reduce it. Therefore, we should expect that in response to a dimming sun, progress on global emissions reductions will slow, and the problems will only continue to grow.
There is only one certain way forward. We must live within our means. We must avoid the temptation of dimming the sun to buy us time which we will almost certainly squander, and instead focus on accelerating the transition away from fossil fuels towards renewables. And let’s keep the sky blue for future generations, if we can.
Stratospheric aerosol injection is not a climate solution
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