Volcanic eruptions help to cool the planet. Can geoengineers harness this in order to combat global warming?
Is there a way to directly prevent global temperature rise? Nature may hold the answer. While volcanic eruptions may evoke images of fire, lava, and ash; the after effects of such heat-filled explosions can lead to drastic short-term global cooling. Geoengineers are working to recreate such conditions to counteract climate change. But should we mess around with our climate in such a major way?
The power of volcanic eruptions to change global climate and weather is somewhat surprising. As far back as AD186, the effects of an eruption at Lake Taupo (New Zealand) could be seen across the world, as records show sunsets appeared redder in both China and Rome for a year following the eruption. Mount Tambora on the island of Sumbawa (Indonesia) sparked what was known as the Year Without Summer in 1816, after a large eruption on 5-15 April 1815 prompted temperatures to drop 0.7ºC worldwide. This volcanic winter triggered failed harvests across Europe, plunging the continent into widespread famine. These eruptions are rare events, but they can have an intense and lingering effect on our planet. In the midst of fears about global warming, this natural process which fuels planetary cooling has garnered increasing attention from the international community.
Hot on the heels of the Montreal Protocol, a massive eruption in the Philippines showed just how powerfully volcanoes can influence our climate. On 15 June 1991, Mount Pinatubo ejected a plume of molten rock, ash and gas 40 km into the atmosphere. From this volcanic debris, 20m metric tonnes of sulfur dioxide gas pierced the stratosphere.
Up in the stratosphere, the sulfur dioxide gas reacted with water to form clouds of tiny sulfate particles. Air currents allowed this sulfuric acid mist to spread, and within three weeks it had enveloped the world. This protective barrier of sulfates happened to be just the right size to reflect some solar radiation away from the Earth. The amount of sunlight which reached the Earth dropped by 10% from 1992-1993, leading to a small, but worldwide, cooling effect of 0.5ºC. The dispersed sunlight following the Pinatubo eruption also made the skies appear much whiter, and fashioned dazzling sunsets worldwide.
Geoengineering: Can we really change the Earth’s climate?
The eruption of Mount Pinatubo sparked ongoing interest into large-scale manipulation of our planet’s environment. As far back as 1974, Mikhail Budyko suggested we cool the earth by launching sulfate aerosols into the skies. But the concept of deliberately modifying the Earth’s climate in such a way has had strong antagonists from the start; mainly because most of the consequences are unknown. Called climate intervention, planetary tinkering and hacking, geoengineering has become something of a dirty word.
The basic premise involves using aircraft, artillery shells, tall-towers, or high-altitude blimps to inject sulfur dioxide — or other sulfate precursors — into the stratosphere. This solar radiation management would cool the planet, and reduce or even reverse sea ice melting and sea level rise. Plant productivity would increase because sunlight would be more diffuse, allowing the terrestrial carbon dioxide sinks to expand.
Political constraints and scientific caution have meant that no real-world experiment has recreated the conditions of an explosive volcanic eruption. Most research looks at how many sulfate aerosols are required to stall global warming, based on measurements from volcanic eruptions. One prominent model released in 2008 suggested that we would need to inject 2-4m tonnes of sulfur dioxide every year just to avoid doubling the carbon dioxide level. Meteorologist Alan Robock, in his paper entitled "20 reasons why geoengineering may be a bad idea" estimated that one Pinatubo size eruption would be required every 4-8 years to balance the rate of emissions.
Despite the potential to lessen the impact of anthropogenic climate change, there are many risks. We know precipitation patterns can change when the stratosphere is altered. This was observed in the aftermath of the 1783 Laki eruption in Iceland, which was known to have weakened both the Indian monsoon and the Sahel rains. Deliberate intervention in the stratosphere could cause similar droughts again in Africa and Asia. As less sunlight will be reaching the Earth, solar power capacity will be reduced, changing the amount of renewable energy we can harvest. Another known after-effect is that the recovery of the Antarctic ozone hole would be delayed, and further Arctic ozone depletion likely. Somewhat less tangible are the potential psychological impacts from the absence of blue skies, not to mention the political and ethical quandaries that arise from manipulating Earth’s delicate climate.
Is geoengineering actually possible?
While modelling the effects of geoengineering is useful, these models and theories about injection are untried and untested, so it is difficult to know if they would work in real life. If solar radiation management is ever going to be used to induce global cooling, engineering studies about how this might be done are necessary.
A group actively researching the feasibility of geoengineering is the Stratospheric Particle Injection for Climate Engineering (SPICE). SPICE evaluates how to deliver aerosol particles into the stratosphere and the costs these might incur. While other groups (like Robock) believe military fighter jets would be the most cost-effective option, SPICE proposes that tethered weather balloons which pump up slurries or gas from the ground are the cheapest, most environmentally friendly option.
Sulfuric acid precursors (synthetic versions of what is released by volcanoes) are the most common candidates for injection. Alongside these, SPICE is also experimenting with titanium dioxide particles. Where most sulfuric acid precursors are toxic — and can cause acid rain in the lower atmosphere — titanium dioxide is non-toxic and stable. What makes it particularly attractive is that it is already produced in large quantities industrially. It is the primary white pigment in paint, a white filler in paper, and is also one of the reflective agents in sunblock which helps block UV radiation. These current uses mean that titanium dioxide is already available in a variety of particle sizes, is cheap to make, and it’s easily accessible.
Even if it is possible, what are the risks?
Humans are inadvertently geoengineering our planet and our climate by our industrial actions. Yet the resounding voice of the scientific community is that any solar radiation management should only be used as a last resort. Reports written earlier this year by the National Research Council of the US National Academy of Sciences, confirm what the Royal Society declared in 2009: manipulating the amount of solar radiation that reaches the Earth is just too risky. All scientists working in this field agree that reducing emissions is the only way to stop climate change, and any use of geoengineering techniques is a temporary solution in case of climatic catastrophe.
These concerns are justified. Just as volcanic eruptions can tweak rainfall patterns around the world, so, too, can planned injections of sulfate aerosols. The monsoons of Africa and Asia are too important to the global population to risk modifying. Any progress made by the Montreal Protocol repairing the Antarctic ozone hole would be set back.
This drastic measure might fix the immediate effects of global warming, such as sea level rise. But reducing the amount of sunlight which reaches the surface of the Earth will not prevent further accumulation of carbon dioxide in the atmosphere, or the acidification of the world’s oceans.
Whether or not to manipulate our climate is a decision that the world needs to make together. The technology is readily available, and it’s not too expensive. Should a nation feel that they have no other option as they face imminent climate change disasters, they just might try it. And who could stop them? You can’t retrieve the particulates once they’re out there. The stratosphere is not isolated, and any injection would have flow-on effects all over the world.
For now, any climate intervention based on replicating what our volcanoes achieve so effortlessly, will remain on the back shelf. Only in case of catastrophic emergency.