The world is warming, perhaps unstoppably – and the only solution is to blanket the sky with aerosols. Sunlight levels will drop, the days will darken, and the planet’s path to overheating will be diverted.
This is solar geoengineering, and it sounds like something more along the lines of science fiction than anything based in reality- and according to some scientists and policymakers, desperate times call for desperate measures.
Not so, concludes a new comprehensive study in Nature Ecology & Evolution. Sustained aerosol injection may temporarily chill the planet, but it’ll wreak havoc on the world’s ecosystems – and, at the very least, it’ll just mask climate change’s underlying engine, that of carbon dioxide emissions.
Volcanic eruptions clearly show us that it’s possible to temporarily cool the planet. Plenty of eruptions unleash sulfur dioxide into the air, and if these compounds meet with water, they quickly transform into sulfuric acid. When they condense, they form aerosol particles, which are incredibly effective at scattering and reflecting sunlight.
Certain eruptions produce so much that they cool the regional, or sometimes planetary, climate. Mount Pinatubo’s eruption in 1991 was the most famous recent example of this; its paroxysm, which released millions of tonnes of sulphur dioxide into the stratosphere, had the effect of reducing the average surface temperature of the Earth for the next 15 months for around 0.6°C (about 1°F).
In short, that is what solar geoengineering is, even if the specifics vary.
A multidisciplinary team, led by the University of Maryland, wanted to simulate a 50-year-long solar geoengineering experiment to find out what exactly would happen if this plan was to go ahead, and the results are fairly troubling.
It’s 2020, and the climate is continuing to warm despite mitigation efforts taking place. The world decides to create this artificial volcano, so to speak, and injects 5 million tonnes (5.5 million tons) of sulfurous aerosols into the skies every year – “equivalent to a quarter of the 1991 Pinatubo Mountain volcanic eruption” – for half a century, at the Equator, so as to ensure equal coverage over both hemispheres.
This would indeed slow global warming down, and species already suffering from rapid warming might temporarily find respite during the experiment.
However, the team’s analysis suggests that this experiment would cause precipitation patterns across the world to suddenly shift.
Also, unlike carbon dioxide emissions - which overall has a lifetime of several centuries in the atmosphere - sulfur compounds linger in the stratosphere for around two years or so. So if or when the geoengineering stops in 2070, the sulfur shield will suddenly sift out of the atmosphere. This would allow sunlight levels to spike, which would cause an incredibly sudden warming effect.
Both of these changes would obviously have a dramatic effect on ecosystems across the planet.
Now, the primary issue with anthropogenic climate change isn’t just that the world is warming, it’s that it’s warming at an unprecedented rate, and it’s this rate change that plenty of species cannot adapt to. This sudden 2070 temperature spike would present them with a similar issue.
In order to elucidate this, the team used climate velocities. Simply put, these describe the speed at which ideal climates for ecosystems move as the climate changes. In general, when the climate warms, the ideal zones moves toward the cooler poles and higher altitudes.
When 2070 comes, then, the warming will move these ideal zones 10.4 kilometers (6.5 miles) per year on land, and 12.8 kilometers (about 8 miles) per year in the oceans. This is more than four times greater, and more than six times greater, than what has occurred under recent climate change.
“Temperature velocities at termination also far exceed those predicted for future climate change without geoengineering,” the team add. The Amazon Basin, Africa, Eurasia and the polar regions will be particularly affected.
Species vulnerable to such sudden changes, particularly those unable to migrate to new ecological niches – including vegetation, coral and plenty of amphibians – would be in dire straits, both as precipitation patterns change during the experiment and as the temperatures snap back after 2070.
In general, the authors note that “repeated switching of the climate signal” from warming to cooling to warming again is known to “negatively affect population persistence, increasing the risk of local extinctions.”
In sum, solar geoengineering would create a brand-new catastrophe, one that would likely cause widespread extinctions.
At this point, the technology nor the international will to engage in such a dramatic feat of solar geoengineering doesn’t exist, but it could. There are also other forms of geoengineering available, including physically storing carbon dioxide emissions in impermeable rock, that could be less harmful to the planet.
In any case, the team concluded that “aggressive emissions cuts remain the most robust way to reduce biodiversity impacts from climate change.” Any development of geoengineering schemes – plenty of which are taking place right now – should proceed with “extreme caution.”
"The benefits and potential risks would have to be weighed in any decision to implement geoengineering," study co-author Professor Alan Robock of Rutgers University told IFLScience.
When asked if he would be more likely to support any other geoengineering scheme out there, Robock simply responded: "No."