Dark clouds cover sky above melted ice floes in Svalbard

Photo: BJ Kirschhoffer / Polar Bears International

Geoengineering – Good Idea? Bad Idea? Do We Need to Know?

By Dr. Flavio Lehner, Chief Climate Scientist



20 May 2024

As the problem of climate change has become more widely recognized, people have started to look for solutions in earnest. There are broadly two ways to counter climate change in the near term: (1) stop emitting greenhouse gases and (2) actively cool the planet. The former is pursued through international climate negotiations as well as bottom-up efforts to curb emissions. The latter, often referred to as “geoengineering,” has long been a taboo topic amongst scientists and in politics. “Climate intervention,” as it has been called more recently, is a deliberate modification of Earth’s climate to reduce the worst outcomes of greenhouse gas-driven climate change. It is akin to treating the symptoms of a disease rather than its root cause.

The most discussed climate intervention idea is Solar Radiation Modification (SRM): the reflection of a portion of the incoming solar radiation back to space — basically a sun umbrella. This could be achieved by spraying aerosols, tiny particles like those that make up a cloud from a wildfire, into the stratosphere (above where commercial airplanes fly), where they reflect sunlight. Another less well-developed idea is to inject salt particles into clouds to make them brighter and thus increase their reflectivity.

Naturally, such ideas invite skepticism from seasoned environmentalists or even just keen observers of history. Humans have a track record of creating new problems when trying to fix existing ones, for example by introducing one invasive species to combat another. On the other hand, one can argue that climate change is an urgent matter that requires creative and multi-pronged solutions.

Here, by answering some common questions around climate intervention and SRM specifically, we provide our current perspective on the issue. This is a rapidly evolving topic, so we expect to update this article in the future.

 Is it a good idea?

  • Climate damages are mounting. The latest assessment report of the Intergovernmental Panel on Climate Change (IPCC) made very clear that we are in the process of fundamentally changing our climate through greenhouse gas warming and that the risk for large-scale disruption of ecosystems increases with every additional tenth of a degree of warming. At the same time, reducing greenhouse gas emissions has proven challenging. While there has been progress towards more carbon-neutral energy production, it is not happening fast enough to prevent further escalation of climate change impacts. Therefore, it makes sense to look for a “quick fix,” a temporary solution to stave off the worst effects of global warming while we work on reducing emissions to get the climate back into equilibrium.

  • Scientific understanding. The primary SRM idea is based on a well-known natural analog: explosive volcanic eruptions inject sulfur dioxide into the stratosphere, creating aerosols. These aerosols reflect solar radiation, leading to a measurable global cooling effect that lasts a bit more than a year — the time it takes for the aerosols to fall back out of the stratosphere. In other words, we understand a good portion of the relevant physics and chemistry from studying past volcanic eruptions. Also, the amount of sulfur dioxide we would need to inject into the stratosphere to combat the warming from greenhouse gases is not huge compared to how much humans already emit into the lower part of the atmosphere through various industrial activities. It would be a significant effort to get the sulfur dioxide into the stratosphere, but costs might be smaller than what scientists estimate the climate change damages from increasing extreme weather events are.

Polar bear standing on the edge of the sea ice

Photo: Kt Miller / Polar Bears International

Is it a bad idea?

  • Risks. Although we understand much about the anticipated impacts of SRM, we have never lived in a world with a thermostat in the form of a perpetual volcanic eruption keeping global temperatures in check. Significant uncertainties remain. Scientists are running hypothetical scenarios of SRM with climate models on big supercomputers to better understand how our climate would change — not just in terms of global temperature, but also in terms of regional rainfall patterns and other important quantities for socio-economic functioning. Are the changes brought about by SRM worse than the impacts from climate change? And for whom? The jury is still out and, therefore, deployment of SRM would currently be a big risk. So far, this research is mostly based on computer simulations, but humans will eventually want to test these ideas in the real world.

  • Remaining issues. SRM is not a panacea. It would mostly combat warming but would do nothing against other climate change issues such as ocean acidification, which is a result of increasing carbon dioxide being dissolved into the ocean. There is also evidence that certain ocean currents, which weaken under warming, would not bounce back to previous levels.

  • Governance and termination shock. Assuming SRM could be deployed without any grave side effects, the question of governance comes up immediately. Who decides how much SRM to deploy? What is the optimal level and for whom? Given current world affairs, it is difficult to imagine that countries would easily agree on these important details. And, perhaps most worrisome, what if SRM were terminated before we managed to curb greenhouse gas emissions? Referred to as “termination shock,” such a scenario would see global temperatures jump to whatever greenhouse gas concentration level we’ve reached within just a few years, a potentially extremely disruptive warming rate.

Delayed action on greenhouse gas emissions. There is concern that with deployment of SRM, momentum towards reducing greenhouse gas emissions would slow, psychologically akin to a patient experiencing relief after his symptoms, but not their cause, are being treated.

Polar bear on sea ice

Do we need to know?

Ever since one of the first proposals for climate intervention was published in the 1990s, the argument prevailed that even to research this topic is an ethically wrong distraction from the real problem. A counterpoint is that in the 1980s computer model-based research revealed that the climate effects of a global nuclear war would be far worse than the bombs themselves, arguably supporting a lasting nuclear peace and serving as an example of the value of researching even some ethically questionable topics.

With mounting climate damages and the increasing willingness of billionaires to privately fund research into SRM, it has now become a topic that cannot be ignored. In fact, recent years have seen reports on SRM from the National Academy of Sciences as well as funding calls from federal science agencies for studying the potential impacts from SRM. Given the importance of SRM for world politics, one can expect that many actors will want to weigh in and that the misinformation campaigns common to politics will affect this topic. It is therefore vital that research into SRM is conducted in the most transparent way possible, including at public universities, to provide society with the necessary information to discuss the pros and cons of SRM. Funding sources and conflicts of interest need to be disclosed, partnerships need to be vetted carefully, and scientific results need to be interpreted against the backdrop of ongoing climate change and the relative failure to address its root cause.

Dr. Flavio Lehner is the chief climate scientist at Polar Bears International and an assistant professor in Earth and Atmospheric Sciences at Cornell University.