Saturday’s enormous eruption of the Hunga Tonga Hunga Ha’apai underwater volcano sent ash 20 kilometres into the stratosphere, accompanied by a 900-kilometre-per-hour sonic boom heard as far away as Alaska and tsunami waves racing around the Pacific.
The blast may be devastating for the people of Tonga and neighbouring areas. The climatic effects of volcanoes are a reminder of Earth’s awesome power but also humanity’s responsibility.
The Tonga volcanoes are sited where the old, cold Pacific geologic plate sinks into the Earth’s mantle beneath the warmer, lighter Australian plate at the Kermadec Trench. When the plate reaches a depth of 100 kilometres or so, its water-rich rocks melt, and the ascending magma creates a volcanic chain. The “Pacific Ring of Fire” reflects this phenomenon, from New Zealand through the Philippines and Japan to Mexico and the Andes.
Volcanoes have a profound impact on short-run climate. They inject ash and, particularly, sulphur dioxide into the upper atmosphere, reflecting the sun’s rays and causing cooling. Halogen compounds may trigger ozone depletion, damaging to human health. Bigger eruptions do not necessarily have the largest effect on climate: it depends on their geographic location, and content of sulphur and other volatile materials.
The super-volcano eruption of Mount Toba in Indonesia about 74,000 years ago may have caused the human population on Earth to dwindle to a few thousand individuals, though this is disputed. Volcanic particles might also have triggered the cold, wet weather of the mid-fourteenth and early-seventeenth centuries, which were followed by famine, plague and war.
The famous Tambora volcano in Indonesia in 1815 created “the year without a summer”, whose gloomy weather inspired Mary Shelley’s classic Frankenstein. A slightly earlier mystery eruption of 1808, possibly a submarine volcano in Tonga, also contributed to this cold period, a time that saw Napoleon’s defeats in the Russian winter and at Waterloo and the collapse of his empire. More recently, the 1982 El Chichon eruption in Mexico and Mount Pinatubo in the Philippines in 1991 cooled Earth by appreciable fractions of a 1°C.
Despite the usual bad-faith commentary, such events do not discredit the knowledge that human emissions of carbon dioxide and other greenhouse gases are driving relentless and dangerous global warming. Volcanic cooling is no more than blips on this trajectory. And volcanic carbon dioxide contributes less than 1 per cent of human emissions yearly.
It is too early to say whether the cataclysm in Tonga will have a wider effect on global climate for a year or two. But it is a reminder that the injection of sulphur dioxide or similar particles into the stratosphere is highly effective in blocking the sun’s rays.
This is the basis for “geoengineering” proposals to offset global warming by artificially carrying reflective particles aloft with aeroplanes or balloons. The material need not be sulphur dioxide; chalk or other stuff could work too.
Compared to the trillions of dollars to retool the global energy economy, geoengineering could be remarkably cheap, as little as $2-2.5 billion annually to cut temperature rises by 1.5°C, the ambition of 2015’s Paris Agreement on climate change.
Geo-engineering, specifically “solar radiation management” (SRM), has often been portrayed as a “last resort”, to be deployed if we perhaps heat the Earth beyond a catastrophic tipping point. Critics have seen it as a dangerous distraction from the essential goal of reducing greenhouse gas emissions. They fear it will be used as a “get out of jail free card” by fossil-fuel interests. A single wealthy country or even mega-rich individual could introduce such a system on their own, over others’ objections.
It does not cut atmospheric carbon dioxide and its negative side effects such as acidification of the oceans. If halted, warming would resume within a year or so at an accelerated pace. And it could result in shifts in precipitation, leaving some areas inundated and others drought-stricken.
Emotions are so strong that campaigners have opposed even the tiniest of experiments, balloons carrying a few kilograms of particles. The scepticism of environmentalists is understandable given the long history of delays, obfuscation and excuses by those seeking a licence to continue polluting.
Similar arguments were made against the idea of adapting to climate change in the 1990s, and against removing carbon dioxide directly from the atmosphere in the 2000s. Now, climate adaptation is accepted as a sad necessity, and an integral part of the Paris Agreement. Carbon dioxide removal on a gargantuan scale by 2050 is the only way that climate models can still hold out any hope of reaching the Paris targets.
Logically, if 1.5°C of warming is still bad, then 1°C would be better. Vulnerable ecosystems, species and human settlements could be saved. So even if we can reduce emissions rapidly, we can offset some of the dangerous possibilities of feedback loops and unexpected consequences by carrying out SRM. That also buys us time to scale up direct removal of atmospheric carbon dioxide.
This is not an argument for rushing into SRM today. But it does encourage learning more urgently. Studying the effects of large volcanoes is useful, but no substitute for well-planned, controlled experiments.
At this moment, we should think first of the people of Tonga, suffering the perhaps catastrophic effects of such an eruption. Climate change will bring disaster, of different types, to a much wider area. Learning from the climatic impact of volcanoes is essential to offsetting some of the consequences of humanity’s own folly.
Robin M. Mills is CEO of Qamar Energy, and author of The Myth of the Oil Crisis