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The clouds that hang low and thick in our skies, reflecting sunlight back into space, merge into the air as the world warms.
The loss will not only trigger larger-than-expected climate change, but new research suggests it could also undermine the potential of future geoengineering solutions.
The idea of seeding clouds with an injection of light reflecting particles to send sunlight back into space – and thus “cool” the planet – is controversial, but has not yet been proven useful. or even doable in the real world.
Some scientists are more worried about the unforeseen dangers of interference with our planet’s climate, while others point out that this climate hacking solution does nothing to combat ocean acidification or the damaging effects on ecosystems. .
It is as good as the clouds in our sky, and in the next century there may be a lot less. Even in the most ideal scenario, where solar geoengineering works without side effects, a new model suggests that it may not be enough on its own.
If the world’s carbon emissions continue to rise unchecked, we will trigger a much larger cascade of warming – cloud seeding or not.
“Therefore, high concentrations of greenhouse gases can trigger substantial global warming by reducing the cooling effect provided by stratocumulus clouds,” write the authors of the new study, “even when all or large part of the effect of greenhouse gases at the top of the atmosphere is offset by solar geoengineering. ”
This is an extreme scenario where carbon dioxide continues to accumulate in the atmosphere at a concentration four times higher than today.
It would take about a century, the researchers say, and yet it could very well happen, even if we spent decades injecting aerosols into the atmosphere.
Today, stratocumulus clouds cover huge swathes of the subtropical ocean, and recent evidence suggests they are responsible for the reflection of around 5 degrees Celsius from global warming in space.
As greenhouse gases build up in the atmosphere, high-resolution simulations show that these clouds will thin out and possibly even dissipate completely. Even under modest warming scenarios, the results show that the subtropical stratocumulus clouds gradually clear up and separate.
Without this protective shield, all of that heat from the sun can then flow freely into the lower atmosphere and oceans of our planet, raising temperatures all over the world even further.
As such, solar geoengineering can only work up to a point, and in the long run, researchers say it does not replace reducing carbon emissions.
“Solar geoengineering is not a foolproof option to prevent global warming,” the authors conclude, “because it does not mitigate the risks to the climate system that arise from the direct effects of greenhouse gases. on cloud cover ”.
Their model illustrates what happens when the increase in CO2 concentrations occur simultaneously with cooling of clouds. As such, it assumes that solar geoengineering actually works and that our emissions will continue unchecked.
But while growing research has linked increased greenhouse gas emissions to a potential tipping point of thinning cloud cover often overlooked in climate models, it is still unclear at what concentration these clouds Start to thin or how it affects their light reflecting abilities.
The warming of the Earth’s surface causes evaporation and an increase in atmospheric humidity, which appears to weaken the cooling at the top of the clouds, much like the fact that the ground takes longer to cool at night in weather. humid as opposed to dry conditions.
The new model is an interesting exploration of what happens when emissions continue while cloud cooling improves, but it’s still a relatively straightforward explanation that doesn’t take seasonal cycles into account. , “noise” in weather data or regional differences.
“The lack of spatial heterogeneity and temporal variability in our simulations makes it difficult to more accurately quantify the range of CO2 concentrations above which stratocumulus rupture can occur or when clouds reform after CO2 the concentrations are lowered ”, admit the authors.
“Caveats and limitations notwithstanding, the findings illustrate a hitherto unrecognized risk in solar geoengineering.”
The risks and benefits of solar geoengineering remain uncertain, and we need a lot more research before we can say for sure whether it is worth pursuing. Clouds are really hard to simulate; to sow them is quite another problem.
For now, reducing our emissions is undoubtedly the best option.
The study was published in PNAS.
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