The Harvard Climate Scientist Who Predicts a ‘Cooling Shock’ Before the Big Heat — and Why Investors Should Care

Climate scientists often pause for a moment before responding to a thought experiment. What if you could rapidly cool the planet by spraying reflective particles into the upper atmosphere and reflecting some sunlight back into space instead of reducing emissions, which takes decades? Imagine being able to purchase time. What would happen if you stopped?
For years, Harvard researchers have been focusing on that final question, which is the most important one for investors. The mechanism is now known as termination shock, a term taken from the language of risk management. Or, to put it more simply, a big heat followed by a cooling shock. The concept is genuinely frightening and deceptively straightforward. If you use stratospheric aerosol injection to artificially suppress global temperatures and then stop the program for any reason (political, financial, logistical), the accumulated warming that was being covered up would quickly resurface. Natural warming occurs in a compressed surge rather than gradually. The planet wouldn’t simply go back to its original location. It would arrive quickly.

A much more modest version of this concept was intended to be tested by Harvard’s SCoPEx project, which is headed by atmospheric chemist Frank Keutsch. tiny balloons. a precisely measured calcium carbonate particle release. An opportunity to watch the behavior of reflective aerosols in the stratosphere under controlled conditions. It literally never lifted off the ground. Harvard declared in March 2024 that Keutsch was abandoning the experiment following years of resistance from environmental organizations, Indigenous communities in Sweden where early tests were scheduled, and ongoing governance disputes. SCoPEx had ended.

The discussion continued despite the shutdown. If anything, it made clear why the discussion is so important. Keutsch had spent years arguing that the world needed more information before making any large-scale decisions regarding solar geoengineering, and that doing careful, limited research was preferable to going into a planetary intervention blind. His detractors were concerned that any research would validate the theory and provide cover for those who favored a technological short cut over the more difficult task of reducing emissions. There were valid points on both sides. There was no clear resolution for either side.
It’s worth stopping to consider the volcanic analogy that lies beneath all of this. The 1991 eruption of Mount Pinatubo in the Philippines released enough sulfur dioxide into the atmosphere to lower average global temperatures by about half a degree Celsius for over a year. It had an impact on crops. The patterns of the weather changed. The cooling was genuine, quantifiable, and completely fleeting. Warming started again after the aerosols dispersed. Researchers examining that incident found it instructive rather than comforting. The experiment had been conducted by nature. The outcomes were convoluted.
David Keith, who attended Harvard for a number of years before relocating to the University of Chicago, has likely done more than anyone else to maintain solar geoengineering as a legitimate scientific inquiry rather than an outlandish theory. He thinks that intentional sulfur dioxide injections into the stratosphere could significantly reduce global temperatures and mitigate the worst immediate effects of warming. He is cautious about recognizing the risks in ways that his detractors occasionally fail to acknowledge. However, in a debate where subtlety is often overlooked, his more general argument—that the technology merits thorough investigation rather than dismissal—has found little comfortable home.
Meanwhile, the university’s own scientists were remarkably open about their worst-case scenarios during a June 2024 Harvard panel titled “What Could Go Wrong?” Assistant professor of Earth and planetary sciences Kaighin McColl outlined what he described as a “plausible scenario” in which portions of the tropics become uninhabitable by the end of the century. Epidemiology professor Caroline Buckee cautioned that heat-related mass migration would put political systems under stress in ways that walls cannot. One statement that stuck was made by panel moderator Daniel Schrag: “Giving people hope based on illusion is not hope.” It’s merely a delusion.
This has practical implications for investors. The costs of climate volatility, such as three significant Atlantic storms in a single season, unending wildfire seasons, and floods in cities built for an older climate, are already starting to be borne by the insurance sector. Even with the best of intentions, the possibility of a geoengineering intervention creates a new class of physical and regulatory risk. Current financial models are not designed to account for abrupt policy reversals, program abandonments in the middle of deployment, or termination shocks that occur over a decade rather than a century.
Solar geoengineering might never leave the lab. The failure of SCoPEx raises the possibility that the governance issues are insurmountable on their own. However, the fundamental physics remains unchanged, and scientists believe that the pressure to try something quick and dramatic will only increase as temperatures rise. It’s genuinely unclear at this point whether that pressure will ultimately overcome the caution. It is evident that the question is no longer solely scientific. It is right in the middle of politics, economics, and the kind of risk assessment that investors should be proficient in but haven’t yet begun to do.