Dimming Sun's rays to cool planet will affect storms too: study

15 November 2017: Injecting billions of reflective particles into the stratosphere could help cool an overheating planet, but would also alter the intensity of tropical storms, researchers said Tuesday.

Depending on the hemisphere in which such aerosols are released, hurricanes in the North Atlantic would become weaker or stronger, they reported in Nature Communications.

Moreover, efforts to engineer lower global temperatures could induce severe drought in northern Africa's Sahel, a region already challenged by climate change, they warned.

With only one degree Celsius (1.8 degrees Fahrenheit) of warming so far compared to pre-industrial times, the world has already seen an upsurge of deadly heatwaves, droughts, and storms engorged by rising seas.

The 196-nation Paris Agreement, adopted in 2015, enjoins the world to cap global warming at "well under" 2 C, and even 1.5 if possible.

But efforts to achieve these goals by reducing greenhouse gas emissions have stalled, leading some scientists to consider "quick fix" engineering solutions that will brake the rise in temperatures.

"In the last decade, solar geoengineering has rapidly garnered attention as a plausible method to counteract global warming," the authors note.

- 'Potentially devastating impacts' -

So-called solar radiation management works by preventing some of the Sun's rays from hitting the planet's surface, forcing them instead back up into space.

Nature sometimes does the same: debris from the 1991 eruption of Mount Pinatubo in the Philippines, for example, lowered the planet's average surface temperature for a year or two afterwards.

Small-scale experiments to test the behaviour of particles in the upper atmosphere are set for next fall, in the state of Arizona.

But the potential for a single country to deploy the technology unilaterally "could have potentially devastating impacts in other regions," they warned.

Earlier research pointed to changes in regional rainfall patterns, and the disruption of monsoons, as potential side-effects of dimming the Sun's radiative force.

Scientists also warn about "termination shock" -- the sudden warming that would likely occur if the system were to fail.

To better understand these pitfalls, a team of scientists led by Anthony Jones of the Met Office Hadley Centre ran state-of-the art climate models measuring likely changes in the ocean and atmosphere.

These showed that adding aerosols in the northern hemisphere would decrease the frequency of cyclones there, while injecting them in the southern hemisphere would have the opposite effect.

The models also showed "potentially devastating impacts" in the Sahel.

The researchers called for the rapid implementation of international regulation to oversee the deployment large-scale solar geoengineering schemes.

"It is going to take a long time before we can predict the effects of solar geoengineering well enough to be confident that we could design an intervention that was both safe and effective," commented John Shepherd, a professor at the University of Southampton, who did not take part in the study.