As time runs out for us to stop the planet from warming further, stratospheric aerosol-based Solar Radiation Management continues to be a possible option. No one believes that it solves the problem – at best it buys more time for us to control our emission of greenhouse gases.
Most scenarios involve injecting sulfates into the stratosphere, but alumina and even diamond dust have been proposed. The idea of course is to shield the Earth’s surface from incoming solar radiation. The most conservative approach would involve injections that would build slowly, complementing CO2 emission mitigation and perhaps CO2 capture, and would be reduced and terminated as mitigation efforts grow. One author calls this the ‘less sub-optimum’ scenario.
It probably is.
We do, however, have plenty of relevant if uncontrolled experiments to think about before jumping for the SRM solution: the eruption of volcanoes. A major eruption, particularly a tropical one, ejects a massive amount of sulfates into the stratosphere 20-40 km above the Earth’s surface. Detected in the ice-cores of Greenland and Antarctica, each of the 16 largest eruptions over the past 2500 years was followed by a decade of colder temperatures, reflected by slower growth in tree ring samples.
So the connection is very clear: reduce the incoming solar radiation with reflective stratospheric particulates, and the planet cools a little.
Sounds too good?
For most major volcanic eruptions we have only the vaguest of information about subsequent biological and sociological effects. Fortunately, we now have a detailed account of the aftermath of one of the largest of these eruptions. Tambora – The Eruption that Changed the World by Gillen D’Arcy Wood, recently published, tells the astonishing tale.
Tambora was a 13,000 ft (4000 m) peak on Sumbawa Island of the Indonesian archiplelago until, in 1815, it blew much of its top half 30-40 km up into the stratosphere. Though no one at the time made the connection, the sulfate ash cloud spread quickly around the planet with cascading cataclysmic impacts over the next three years. Wood has explored the events and connected them convincingly.
In Europe, the US Atlantic States, Yunnan Province in China, Bangali India, Indonesia – crops failed for two years, harvests were lost to frost, drought and floods, while starvation and famine killed huge numbers of people, forced populations into riots and survivors into emigrants, tearing apart the social fabric of communities and families. Cholera raged in Bengal, Typhus spread though Ireland. Meanwhile, Shelley and Byron wrote sensitive apocalyptic poems based on what they saw in Switzerland while Turner painted his famous sunsets in England.
Records of Tambora’s impact on Africa, South America and Australia don’t seem to exist. But though so much of Europe and eastern North America was devastated, Russia and the US states and territories further west were unaffected: there farms flourished and farmers sold their grains at high prices to starving Europeans and Atlantic Americans. Destitute eastern Americans migrated west to the rich grain-growing land around the Mississippi.
And then in 1818 the skies finally cleared, bumper harvests returned, and the misery receded. Some repercussions persisted – shifts in attitudes about colonialism in India and optimism in the US, a shift to opium poppy growing in Yunnan, and cholera drifted on around the planet. As well, the US western farmers lost their market and their farms, bringing on the US depression of 1819-22.
During the three year impact of Tambora’s eruption, global mean temperatures appear to have abruptly dropped only about 1 degree Centigrade, yet many places around the planet experienced the crop failure, famine, epidemic disease, and catastrophic social disruption. Wood’s account is both gripping and very worrisome.
So we are well warned. If we do too little about the rate of current climate change, the scenarios are bleak. If we intentionally embark on Solar Radiation Management, we will without doubt provoke a cascade of unintended effects that could be just as bleak.
There is no quick fix. Our only option remains what it has always been. The importance of the upcoming Paris Conference on Climate Change grows ever greater.