‘If something can shave off just half a degree, that means millions fewer impacted by heatwaves, crop failures or flooding.’
By
As global temperatures climb and extreme weather events become more frequent, scientists are exploring the use of solar geoengineering, a set of different measures all geared towards reflecting sunlight and cooling the Earth.
“The world is making progress on emissions,” says solar geoengineering researcher Dr Pete Irvine of the University of Chicago, “but even if every country meets its current pledges, we are still tracking towards more than 2.5 degrees of warming by century’s end.”
That level of warming could lead to severe impacts such as loss of biodiversity, health crises and unchecked polar melting, adds Irvine, who the cofounder of SRM360, a nonprofit hub investigating ways to reflect the heat of the sun.
There are other strong voices in the scientific community that argue solar geoengineering measures could – if successful – simply relieve the urgent pressure to implement necessary deep cuts to greenhouse gas emissions.
Irvine argues that emissions cuts need to happen come what may, and that solar geoengineering should not be seen as a substitute for emissions cuts or carbon removal schemes but as an added measure to help cool the planet.
Eliminating emissions will stop climate change from worsening, but to actually bring temperatures back down to a safer, more stable level will need removal of hundreds of billions of CO2 already in the atmosphere, says Irvine. “Solar geoengineering could help us manage risks along the way.”
Scientific techniques that seek to reflect the sun’s energy back into space, and thus cool Earth, are all referred to as solar geoengineering, or as sunlight reflection methods (SRM). There are two leading strategies aiming to do this.
There is stratospheric aerosol injection (SAI), which involves releasing fine, reflective particles, such as sulphur compounds, into the upper atmosphere. Scientists say it could reduce global temperatures by 1 degree if deployed widely.
The other option is marine cloud brightening (MCB). The goal here is to make low-lying clouds more reflective of sunlight. This is achieved by injecting tiny particles of sea salt into the clouds – making them brighter, and increasing their ability to reflect sunlight away from the Earth and back into space.
Irvine says that although SRMs are beneficial, none of them alone can fully address the root cause of the warming problem: the build-up of greenhouse gases in our atmosphere. “They can’t stop acidification of oceans or repair ecosystems already damaged by climate pressure.”
Their implementation can carry a risk of harmful side effects. Measures to introduce SAI, for instance, could result in increases, albeit mild, in acid rain, and potential delays in healing of the ozone layer.
And there is even a risk of a “termination shock”, Irvine adds, which is a risk of a rapid spike in temperature if SRMs were started and then abruptly halted.
The global politics involved could be tricky, too, he says, if countries become suspicious of each other’s actions or motives. “Imagine a powerful country deploying SRM unilaterally. Even if their intention was to benefit everyone, perception matters. What happens if droughts or storms are blamed, rightly or wrongly, on their actions? The risk of conflict, or global mistrust, is real.”
