Interest in—as well as concerns about—solar radiation modification (SRM, also known as solar geoengineering) has gathered momentum in recent months: from stunt deployment by a commercial startup to objections expressed in the media that Africa be used as a laboratory for environmental manipulation and the reactions to them, from plans by eminent scientists to refreeze the Arctic to rare bipartisan U.S. Senate support for scientific research into the idea.
Interest in—as well as concerns about—solar radiation modification (SRM, also known as solar geoengineering) has gathered momentum in recent months: from stunt deployment by a commercial startup to objections expressed in the media that Africa be used as a laboratory for environmental manipulation and the reactions to them, from plans by eminent scientists to refreeze the Arctic to rare bipartisan U.S. Senate support for scientific research into the idea.
As the latest report from the Intergovernmental Panel on Climate Change (IPCC) made clear, the world is now more likely than not to exceed—for possibly several decades—the 1.5-degrees-Celsius goal, and the impacts of a warming world are increasingly being felt. Climate policymakers are anxious and unsure about what the future may bring, but a growing number are aware that the option to use—or not use—SRM may well be part of the discussion.
SRM would aim to address a symptom of climate change by reflecting more sunlight back into space in order to directly reduce Earth’s temperature. There are several different types of SRM, including brightening marine clouds, painting rooftops white, covering glaciers, and injecting aerosols into the stratosphere. This article focuses on the latter.
Governments, the United Nations, and even the private sector are devoting greater attention to the possible risks and benefits of using these techniques to help manage the perils from temporarily overshooting the temperature goal of 1.5 degrees Celsius.
But with increasing knowledge, critical questions have emerged. Should there be a single finger on the global thermostat? Under which international process or institution would momentous decisions on whether or not to deploy be made, and will all countries and concerns be represented? Will more research and further awareness of SRM undermine global momentum to reduce emissions, remove atmospheric carbon, and strengthen adaptation? What would be the implications of unilateral deployment? How would an international agreement on SRM—of any nature—be enforced?
At present, there is no comprehensive international governance for these techniques. According to the IPCC report, the lack of a formal, robust international governance for SRM poses a risk in itself, potentially leading to unilateral, uninformed actions and forcing governments to react hastily in a crisis.
Consider the balloons launched in Mexico last year as a small-scale commercial SRM intervention carried out by a U.S.-based startup selling “cooling credits” for releasing high-altitude balloons with aerosols. No prior consultations with the government or local communities were undertaken. Initial deployment prompted the Mexican government to announce it would block such activities. The company has since continued launches from the United States, which has not taken any action thus far.
For the last six years, we at the Carnegie Climate Governance Initiative have been meeting with representatives of governments and civil society organizations around the world and encouraging them to address the lack of governance for SRM. While some progress has been made, the issue deserves more attention—and soon.
The most widely researched, and controversial, type of SRM is stratospheric aerosol injection. If deployed at scale, it would quickly lower the global mean temperature and affect every country and ecosystem in the world, but not necessarily equally.
Currently, stratospheric aerosol injection exists only in computer models and is not ready for deployment, though some outdoor experiments have been attempted and others implemented. The premise behind it, however, mimics what happens during a volcanic explosion when sulfur aerosols are released into the lower stratosphere. The aerosols reflect some sunlight back into space—dimming the sun temporarily and thus lowering the global temperature.
Some scientists suggest that airplanes could regularly release reflective aerosols into the lower stratosphere, and that Earth’s temperature would cool significantly within a matter of months. No other method for addressing warming could bring such rapid results, with the lowest price tag for direct costs on the order of $20 billion annually per 1 degree Celsius of cooling.
Therein lies part of this technique’s allure—and danger. SRM is not a solution to climate change as it does not address its root cause: excess greenhouse gas emissions. Only reducing emissions and removing atmospheric carbon can do that. SRM addresses one of its symptoms: temperature rise. According to the IPCC, at best, it could be a supplement to overall efforts that address climate change.
However, many worry that SRM could be seen by some as a way to provide a quick, bandage-type solution to the climate crisis—one that doesn’t require the world to decarbonize, including through the radical transformation of unsustainable lifestyles. Attempts at such a nonsolution would be completely erroneous, but the temptation could remain.
Overshooting the Paris Agreement temperature goals entails risks for both humanity and the ecosystems we depend on for survival. As U.N. Secretary-General António Guterres has said, “Every fraction of a degree matters.” Deploying SRM also entails risks—known and unknown—and must be seen in the context of a world that is hotter than the one any previous generation has experienced, which will become hotter still over the period of an overshoot.
The hard truth is that there are no risk-free options.
If stratospheric aerosol injection were to be used, it would need to be deployed—and governed—continuously for decades, potentially for generations, depending on the world’s progress in reducing emissions and removing excess carbon already in the atmosphere.
Models show that both its risks and benefits would be uneven. It could, for example, harm the ozone layer, upset monsoon cycles, and trigger or exacerbate potential conflicts. Suddenly terminating its use, because either governance lapsed or deployment was sabotaged, could be devastating for biodiversity.
Conversely, its use could potentially alleviate suffering for millions of people living in regions with extreme heat, saving lives and livelihoods and reducing many of the impacts of a warming climate.
Should humanity forgo learning about such techniques, thereby accepting the risks from overshooting 1.5 degrees Celsius and the potential for climate tipping points to be triggered? Or should we deliberately alter the climate using SRM? Do we have the right to do that—or not to do that? How might the world make such a decision? Based on whose authority?
The vast majority of government representatives we have spoken with want to learn and understand more about the risks, benefits, and governance challenges of SRM before they make decisions.
There are far more questions than answers. But one thing is clear: whether you agree or disagree with SRM as a potential emergency tool to temporarily supplement existing efforts, the risks of the current lack of governance need to be addressed.
A recent report published by the U.N. Environment Programme, for example, calls for a “robust, equitable and rigorous trans-disciplinary scientific review process to reduce uncertainties associated with SRM and better inform decision-making.” Some scientists have called for banning the use of SRM and related research, while others are calling for more or more balanced research. A key governance gap to be filled relates to whether or not to pursue research, and if so, how.
Many government representatives we have spoken with also recognize the importance of public engagement and the need to involve a broad swath of society with different views and perspectives to engage in national and international informed discussions on this issue.
They also recognize the need to proceed with governance frameworks that involve all countries; recognize an increasingly likely temperature overshoot; support agreed objectives, such as the global Sustainable Development Goals; and, most importantly, do not undermine progress on reducing emissions and removing carbon from the atmosphere, both of which are essential for addressing climate change.
However, they are unsure which current international framework is best suited for which dimension of governance. Should one make use of existing international treaties, such as the United Nations Framework Convention on Climate Change? Should one pursue decisions in fora like the U.N. Environment Assembly? Or would it be more useful to aim for less formalized arrangements of governance?
Our conversations in the last few years indicate that this September, policymakers at the U.N. General Assembly, with its universal representation and ability to address interlinking issues, are well placed to deliberate on how to address the risks of lack of governance around SRM, including by setting the scene to enable and support learning about these techniques; giving guidance to other intergovernmental processes to pursue work related to SRM; considering options that enable and take into account the informed views of all countries and stakeholders; and laying the groundwork for some very difficult decisions in the coming years.
International agreements can take years to negotiate, though, especially when it comes to preserving the global commons. And time is precisely what the world doesn’t have when it comes to addressing climate risks. Building on informal discussions already underway, it’s time for policymakers to accelerate their engagement on this issue. Delaying this conversation only magnifies the already considerable risks.