A depressing study shows a big problem with using cloud seed to solve global warming

The clouds that hang low and thick in our sky, reflecting sunlight into space, are melting into thin air as the world warms.

The leak will not only trigger more climate change than we expected, 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 reflect sunlight back into space – thus “cooling” the planet – is controversial, but has yet to be proven useful or even feasible in the real world.

Some scientists worry about the unforeseen dangers of further intruding into our planet’s climate, while others point out that this climate hacking solution does nothing to address ocean acidification or negative ecosystem effects.

It is also as good as the clouds in our sky, and in the next century there may be far fewer of them. 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 global carbon emissions continue to rise without restriction, we will trigger a much larger warming cascade – cloud seeding or not.

“Hence, high concentrations of greenhouse gases can trigger substantial global warming by reducing the cooling effect provided by the stratocumulus clouds,” the authors of the new study write, “even when all or most of the greenhouse gas effect at the top of the atmosphere is offset by solar geoengineering. ”

This is an extreme scenario in which carbon dioxide continues to accumulate in the atmosphere at a concentration four times greater than it is today.

It would take about a century, the researchers say, and yet it could still happen very well, even if we spent decades injecting aerosols into the atmosphere.

Today, stratocumulus clouds cover large areas of the subtropical ocean, and recent evidence suggests they are responsible for reflecting about 5 degrees Celsius of global warming into space.

As greenhouse gases accumulate in the atmosphere, high-resolution simulations show that these clouds will thin out and possibly dissipate completely. Even in modest warming scenarios, the results show that subtropical stratocumulus clouds gradually thin out and break up.

Without this protective shield, all of the sun’s heat can then sink freely into our planet’s lower atmosphere and oceans, further increasing temperatures around the world.

As such, solar geoengineering can only work up to a point, and in the long run, researchers say it cannot replace cutting carbon emissions.

“Solar geoengineering is not a safe 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 CO is increased₂ concentrations occur simultaneously with increasing cloud cooling. As such, it is assumed that solar geoengineering really works and that our emissions will continue out of control.

But while growing research has linked rising greenhouse gas emissions to a potential tipping point in cloud cover thinning that is often overlooked in climate models, it’s still unclear at what concentration those clouds begin to thin or how. this affects their ability to reflect light.

Surface warming on Earth leads to evaporation and increased atmospheric humidity, which appears to weaken the cooling of the top of the clouds, much like how the ground takes longer to cool down at night in wet weather than in dry conditions.

The new model is an interesting exploration of what happens when emissions continue as cloud cooling improves, but it is still a relatively simple explanation that does not take into account seasonal cycles, “noise” in the weather data or regional differences.

“The lack of spatial heterogeneity and temporal variability in our simulations makes it difficult to quantify the CO interval more precisely₂ concentrations on which the rupture of the stratocumulus can occur or when clouds reform after CO₂ concentrations are lowered, “admit the authors.

“Despite the caveats and limitations, the results illustrate a hitherto unrecognized risk of solar geoengineering.”

The risks and benefits of solar geoengineering remain uncertain and we need a lot more research before we can say for sure if it’s worth pursuing. Clouds are really hard to simulate; sowing them is another matter entirely.

For now, reducing our emissions is still arguably the best option.

The study was published in PNAS.