To avoid dangerous levels of global warming, the world must limit average temperature increases to no more than 1.5℃ by the end of the 21st century relative to the preindustrial era. This requires global emissions of planet-warming greenhouse gases to be reduced at a speed that looks increasingly unrealistic. In less than 7 years, the worldwide emissions of carbon dioxide from fossil energy and other sources would have to be cut in half.
As the world is about to cross the line separating climate change that is harmful yet manageable from climate change that is dangerous and potentially uncontrollable, voices are getting louder calling for an emergency measure: blocking sunlight to stop global warming.
The idea of artificially cooling the planet by blocking small amounts of incoming solar energy has been a matter of intense debate for more than two decades. At first, it was a speculative idea at the fringes of climate science. Today, it is a high-stakes political issue being discussed by governments, international organizations, think tanks, and diverse interest groups.
It works like this: by injecting reflective particles into the stratosphere, a small amount of solar energy would be reflected back into space before it reaches the surface of the planet. Redirecting perhaps 2% of incoming solar energy in this manner could effectively stop global warming overnight and at costs that are ridiculously small compared to the costs of transitioning towards 100% renewable energy systems over the next three decades while also slashing emissions from transportation, agriculture, and other sources.
This idea is called solar geoengineering, solar radiation management, or albedo modification and we know that it would work: large volcano eruptions transport sufficient amounts of sulfur dioxide into the stratosphere to reflect enough sunlight for creating short-term anomalies in the historical temperature record. But there are immense risks: not only environmental but also social and political.
It works like this: by injecting reflective particles into the stratosphere, a small amount of solar energy would be reflected back into space before it reaches the surface of the planet. Redirecting perhaps 2% of incoming solar energy in this manner could effectively stop global warming overnight.
A global solar geoengineering program would require stratospheric injections of sulfur dioxide, or similar reflecting materials, of millions of tons per year. While this would stop global warming, it is not entirely clear what side effects, possibly including the catastrophic type, would result. Environmental risks include damage to the ozone layer or reduced photosynthesis in plants. It is also important to understand that, while solar geoengineering is an effective method for stopping global warming, it does not address the cause of the problem, that is, the emission of unsafe volumes of greenhouse gases from various human activities. Even if solar geoengineering would be deployed, all of the greenhouse gases that have built up in the atmosphere would still be there – and would continue rising as we would continue emitting.
If the episode with Make Sunsets shows anything, it is that we simply cannot rely on developers and entrepreneurs to deliver safe and effective technological solutions by themselves.
This means that some important impacts of climate change would continue to get worse, notably the increasing acidity of the world’s oceans due to their absorption of carbon dioxide, with catastrophic consequences for marine life. It also means that an artificial solar mask might discourage governments and industries from rapidly switching to cleaner and greener technological and economic solutions – after all, temperature increases are temporarily under control. Then there is the problem of termination shock: reflective particles would have to continuously be injected into the stratosphere, at high volumes and through technical means that may be demanding, and any sudden discontinuation would remove the global filter and make temperatures rapidly rebound to their natural, higher level in line with atmospheric greenhouse gas stocks. As the problem of global warming is less about the amount of temperature increases but their rate, such a sudden temperature shock would likely have cataclysmic global repercussions.
The possibility of termination shock is not the only aspect of solar geoengineering that requires us to think long and hard about potential governance solutions. Another major question is how to stop a single actor from going ahead with large-scale and global climate manipulation. If China, or the United States, for that matter, would decide in the near future that climate impacts are becoming existential, they might opt to move ahead with a unilateral program for solar geoengineering. If that were to happen, who would be in a position to stop them? In fact, the United States is currently starting up a new federal research program to look into possibilities for solar geoengineering. China has a history of using technical means for weather manipulation and might also be inclined, at some point in the future, to deploy a global solar shield regardless of what the rest of the international community prefers.
It is also important to understand that, while solar geoengineering is an effective method for stopping global warming, it does not address the cause of the problem, that is, the emission of unsafe volumes of greenhouse gases from various human activities.
We can currently witness a somewhat silly premonition of this dark future. Make Sunsets, a US-American startup company claims to have recently commenced stratospheric aerosol injections by launching weather balloons from Mexico (presumably to reduce legal and regulatory risk). Through their website, they are offering for the public to buy “cooling credits” – certain amounts of global cooling that companies or governments may choose to buy, somewhat analogous to the way that certain carbon markets work, yet conceptually flawed and based on shaky mathematical calculations. What if this were India instead, confronted with catastrophic risk to its vast coastal areas from rising sea levels? Or a club of small island states threatened with the physical disappearance of their territory into the sea?
If the episode with Make Sunsets shows anything, it is that we simply cannot rely on developers and entrepreneurs to deliver safe and effective technological solutions by themselves. As climate change accelerates, calls for the deployment of solar geoengineering will get louder. Developing robust frameworks for responsible governance is thus a matter of growing urgency. A new initiative of scientific stakeholders recently began advocating for an international non-use agreement for solar geoengineering. Conversely, the new Climate Overshoot Commission of the Paris Peace Forum is presently exploring potential deployment options to reduce climate risks. The politics are certainly controversial and the debate is contentious. But this is a necessary part of the process.
As long as we do not leave it up to the developers and entrepreneurs.
Dr. Florian Rabitz is a chief researcher in the Research Group Civil Society and Sustainability at the Faculty of Social Sciences, Arts and Humanities. His work explores the role of new and emerging technologies in global environmental politics.