Futuristic climate solution could spell disaster for Earth's own defenses

Among other hard lessons, 2020 shows that climate change's deadly effects are no longer just a terrifying future — they are happening, now.

Fires, floods, and drastic climatic swings are affecting people and animals across the world, and even our most desperate solutions might not save us. Rather, it could destroy one of our greatest natural protections.

But that doesn't mean we should throw in the towel just yet. A new study suggests that one of the most-debated future-proofing ideas, solar geoengineering, may not be the solution to our present crisis. But that doesn't mean it can't still play a crucial role in solving our planet's climate problem.

Solar geoengineering is hotly debated among climate scientists. Instead of focusing on changes we can make on Earth to mitigate climate change, solar geoengineering takes the fight directly to the source: the Sun.

Here's how such an approach would go down: Scientists would inject tiny, reflective particles, like sulfur dioxide, into the Earth's atmosphere to act as a shield against incoming sunlight. Similar to how a windshield screen keeps the inside of your car from heating up on a summer day, this aerosol shield would (in theory) limit the Earth's warming and balance rising levels of CO2.

Scientists have voiced concerns about the potential problems with this solution in the past. Now, a team of scientists from the California Institute of Technology and the Pacific Northwest National Laboratory argues the "solution" could actually endanger one of Earth's natural climate protections — clouds.

In fact, solar geoengineering could cause certain kinds of clouds to essentially disappear from the sky entirely, the study suggests.

"[T]here is another set of risks of solar geoengineering that has not received the attention it deserves," write the authors. "[E]levated [greenhouse gas] concentrations may trigger substantial global warming by reducing the cooling effect stratocumulus clouds provide, even when all or much of the effect of [green house gas] at [the top of the atmosphere] is compensated by solar geoengineering."

Their findings were published in a new paper on Monday in the journal Proceedings of the National Academy of Sciences.

See also: Could solar geoengineering solve African poverty?

Cloud science — The researchers used climate modeling to imagine how a century of solar geoengineering would impact the planet's cloud cover. In particular, they wanted to see how the cloud coverage above subtropical oceans would be affected.

These clouds play a huge role in regulating the planet's overall heat, cooling it by as much as 14 degrees Fahrenheit. The clouds are cooled by a process called "radiative cooling," where by infrared radiation balances out the absorption of energy from the Sun. This drives turbulent air downward for a cooling effect. But elevated greenhouse gas levels, which solar geoengineering would not address, would disrupt this cooling process.

Similar to how it is easier for the air outside to cool down when it's dry than when it's humid, the authors explain that increased levels of CO2 and water vapor in the atmosphere weaken the radiative cooling effect these clouds rely on. As a result, the clouds can begin to thin.

Unintended consequences — The models suggest unabated levels of greenhouse gas regardless of overall climate warming, would have detrimental effects on this crucial cloud coverage within 100 years. This would have a knock-on effect on the planet's resultant temperature. Losing these clouds would trigger an onslaught of global warming, up to 9 degrees Fahrenheit, the study finds.

Solar geoengineering is not a fail-safe solution to our climate problem, the researchers say. But that doesn't necessarily mean it can't play a role at all, the study's first author and professor of environmental science and engineering at CalTech, Tapio Schneider, explains to Inverse.

"Solar geoengineering is still feasible on timescales of decades," Schneider explains. "[It] can be combined with any other method that reduces the accumulation of greenhouse gases in the atmosphere. This includes emission reductions, carbon capture — for example in smokestacks — and storage, or ways of scrubbing CO2 from the atmosphere."

Ultimately, these results demonstrate that there's still a lot left and learn about the benefits, and the shortcomings, of geoengineering, Schneider says.

And that is before we even get to "the thorny questions of governance, ethics, and geopolitics" such climate hacking would trigger, Schneider says.

Looking ahead, Schneider and his team hope to refine their models to see how these theoretical, high-tech solutions could shape our planet's future — and whether we are setting ourselves up for a fall.

Abstract: Discussions of countering global warming with solar geoengineering assume that warming owing to rising greenhouse-gas concentrations can be compensated by artificially reducing the amount of sunlight Earth absorbs. However, solar geoengineering may not be fail-safe to prevent global warming because CO2 can directly affect cloud cover: It reduces cloud cover by modulating the longwave radiative cooling within the atmosphere. This effect is not mitigated by solar geoengineering. Here, we use idealized high-resolution simulations of clouds to show that, even under a sustained solar geoengineering scenario with initially only modest warming, subtropical stratocumulus clouds gradually thin and may eventually break up into scattered cumulus clouds, at concentrations exceeding 1,700 parts per million (ppm). Because stratocumulus clouds cover large swaths of subtropical oceans and cool Earth by reflecting incident sunlight, their loss would trigger strong (about 5 K) global warming. Thus, the results highlight that, at least in this extreme and idealized scenario, solar geoengineering may not suffice to counter greenhouse-gas-driven global warming.