To stabilize global temperatures, humanity needs to replace the energy basis of industrial modernity. We must build vast constellations of wind and solar farms, lace continents with high-voltage transmission lines, replace all internal combustion engines with batteries, decarbonize heavy industry, increase the energy efficiency of our buildings, expand mass transit, and promote housing density, among myriad other things.
Unless we just need to dump 139 billion gallons of extremely white paint across roughly 2 percent of the Earth’s surface.
This week, the New York Times reported on Xiulin Ruan’s extraordinary feat of pigmentary engineering. A researcher at Purdue University, Ruan has spent years trying to develop a maximally reflective type of white paint, one that could bounce upwards of 95 percent of the sun’s rays off of any given surface and then back out into deep space, cooling the planet in the process. Now, Ruan’s team has engineered a shade that reflects 98 percent of sunlight.
Cover a building in Ruan’s white paint, and you’ll render its surface eight degrees cooler than the air temperature by day, and 19 degrees cooler by night. Such paint would thereby enable that building to use up to 40 percent less air-conditioning to achieve the same internal temperature.
More stunning than these local effects are the paint’s potential global ones. The substance redirects so much light and heat back into space that, according to one calculation, it could offset the impact of ongoing carbon emissions if we could somehow pour it over 1 to 2 percent of the entire planet.
Of course, this is not an especially practical proposition. After all, 71 percent of the Earth’s surface is water. You would therefore need to cover a land mass roughly the size of the United States in ultrawhite paint in order to stop the planet from absorbing more heat than it emits and stabilize global temperatures. And you wouldn’t actually want to concentrate such paint in a single contiguous area, as this would have severely disruptive implications for the regional climate. Rather, you would need to distribute giant expanses of white paint at strategic locations around the planet.
Even if humanity could execute such a quixotic plan, doing so still wouldn’t actually obviate the need for decarbonization. Paint erodes, after all. Relying exclusively on reflected sunlight to compensate for the greenhouse effect would be perilous.
Nevertheless, Ruan’s invention calls attention to the fact that humanity has the capacity to not just mitigate future warming, but actually reduce global temperatures through feats of engineering. Consciously manipulating the reflectivity of the Earth’s surface and atmosphere, or the alkalinity of its oceans, are risky endeavors. But they are (almost certainly) less hazardous than tolerating more than 1.5 degrees Celsius of warming above preindustrial levels. In any case, there is simply no way to improve climatic conditions, rather than merely constraining their degradation, without some form of geoengineering.
Ruan’s white paint can play a role in cutting temperatures, as can techniques for reducing the acidity of the ocean and increasing its absorption of CO2. Eventually, it is possible that we will develop economically viable means for sucking carbon out of the atmosphere and burying it in the Earth. At present, however, there is only one logistically and economically viable means of engineering a cooler planet: injecting sunlight-reflecting aerosols into the stratosphere, also known as solar-radiation management.
Within the climate movement, there are (at least) two prominent objections to dedicating significant funding to geoengineering research and development. One is that geoengineering presents a moral hazard: If people took the first two paragraphs of this article literally and concluded that we can carry on burning fossil fuels in perpetuity, so long as we pump aerosols into the atmosphere, lime into the oceans, and white paint across every stretch of asphalt, then the political impetus for decarbonization would be lost. Humanity would then wager its long-term survival on a collection of pseudo-fixes that only work temporarily and will present greater risks the more we must rely on them.
A second objection is that geoengineering in general — and solar-radiation management in particular — is a hubristic endeavor. Any attempt to impose our will over systems as unintelligible as the troposphere can only lead to ruin. As Naomi Klein has argued, “To fix the crud in our lower atmosphere by pumping a different kind of crud into the stratosphere” would be to risk causing “the earth to go wild in ways we cannot imagine.” After all, the Earth’s “self-organizing, complex, adaptive systems” possess “emergent properties that simply cannot be predicted.”
These concerns are not unfounded. But they are nonetheless unpersuasive.
The green transition is unfolding at a calamitously slow pace. But it is underway. The world’s most powerful governments have all poured substantial (if inadequate) funds into decarbonization. Carmakers are planning for a future free of internal combustion engines. Renewable energy is becoming cost-competitive with fossil fuels. Much of the world’s economic elite is literally invested in a low-carbon future. We are not on track to phase out fossil fuels at the speed necessary for meeting the IPCC’s goals. But the path of least resistance is no longer an indefinite extension of the carbon economy. There is little risk that increasing public investment into the research and development of geoengineering techniques will lead the world to abandon decarbonization.
There is no question that solar geoengineering presents significant risks. Adding aerosols to the atmosphere could exacerbate air pollution and damage the ozone layer. It would also have disparate impacts on different regions of the globe. Concentrate aerosol particles in a particular stretch of the stratosphere, and you may render one nation more agriculturally fertile and another more vulnerable to drought. The geopolitical implications of solar-radiation management could therefore prove explosive.
Still, the risks of manipulating the stratosphere must be weighed against those of not doing so.
Cooling the Earth by pumping aerosols into the atmosphere would not actually be a new endeavor for humanity. We have been unintentionally doing precisely that for well over a century. Coal-fired power plants, diesel-fueled cars, and cargo ships all emit vast quantities of sulfur dioxide and other aerosols that can cause asthma and cancer when they get into human lungs. But those same pollutants also cause temperature reductions when they get into the atmosphere by reflecting sunlight back into space. According to the IPCC’s estimates, manmade aerosols have been cooling the planet by as much as 0.8 degrees Celsius.
This reality complicates efforts to limit global warming. After all, decarbonization requires shuttering coal plants, getting diesel trucks off the road, and lowering emissions from cargo ships, airplanes, and other industrial sectors. And yet, the more we eliminate such sources of air pollution, the fewer aerosols there will be in the atmosphere. This is because, unlike carbon, sulfur dioxide tends to fall out of the stratosphere within two years of its emission. Thus, if we stop pumping more aerosol pollutants into the atmosphere, the scrim of sulfur that’s been tempering global warming this whole time will quickly dissipate, and temperatures will spike by nearly one degree.
Of course, a total cessation of aerosol pollution is not going to happen. But even a modest increase in global temperatures, as a result of lost aerosols, could make restricting warming to 1.5 or even two degrees Celsius all but impossible.
Thus, intentionally injecting sulfur dioxide into the stratosphere is quite plausibly a precondition for keeping future warming within tolerable bounds, at least until global decarbonization has been fully achieved.
Solar geoengineering’s great promise, however, is not that it can merely prevent a sudden spike in global temperatures, but that it can actually bring about a reduction in such temperatures. David Keith, a professor of applied physics at Harvard, estimates that injecting 2 million tons of sulfur annually into the stratosphere could reflect away enough sunlight to cool the planet by one degree. Which is to say, it could bring global temperatures back down to roughly their preindustrial level.
This is not something that even rapid and total decarbonization could achieve. It will take thousands of years for the greenhouse gasses we’ve already emitted to exit the atmosphere. Humanity is currently poised to greatly exceed the IPCC’s 1.5-degree Celsius target for warming. And even if we did miraculously achieve that goal, the ecological consequences of even that much warming would still be devastating for large portions of humanity. A little more than one degree of warming is already causing upwards of 100,000 deaths from heat exposure every year; invoking more frequent droughts in some regions and floods in others; increasing the intensity and frequency of natural disasters; and threatening to destroy many low-lying communities. What’s more, we do not know exactly what amount of warming will be sufficient to trigger feedback loops that accelerate further warming and environmental destruction.
Needless to say, climactic changes that render water and agriculturally viable land more scarce in some regions are liable to increase geopolitical conflict. And such changes will also alter complex ecologies in ways that we cannot fully anticipate. Therefore, declining to reduce global temperatures through geoengineering entails many of the same risks as injecting aerosols into the sky.
The critical question is how the respective risks compare. Answering that with adequate confidence will require more research. But the existing literature suggests that the benefits of reducing global temperatures by one degree would outweigh the costs. According to Harvard’s Keith, any consequent increase in air-pollution deaths from adding sulfur to the air would be 10 to 100 times smaller than the resulting decrease in deaths from extreme heat.
Crucially, one of solar-radiation management’s chief limitations — the fact that it must be repeated ceaselessly to maintain its effects — also mitigates the risk of attempting it: If we find that the consequences of intentional solar geoengineering are unfavorable, the sulfur we added to the atmosphere will dissipate within two years.
Concern for equality and social justice also militates in geoengineering’s favor. In the West, there is a tendency to see solar engineering as a last resort, one we should reach for only once warming has reached an unbearable level. But to no small extent, catastrophic climate change is already here; it’s just unevenly distributed. For people occupying the world’s hottest and most arid regions, or its poorest low-lying islands, 1.5 degrees of warming will be sufficient to radically degrade living conditions, if not send them into exile.
Those most vulnerable to climate change are, generally, also among the populations least responsible for it. Poor nations have emitted far less carbon than rich ones, and they are also far less able to insulate their citizens from the consequences of climatic changes. Combine this fact with the reality that equatorial regions are disproportionately poor, and it is clear that acquiescence to 1.5 degrees of warming will impose disproportionate costs on the world’s least fortunate, and most blameless, populations.
Therefore, if we wish to prioritize the interests of the most vulnerable, we must deem abstention from geoengineering enormously hazardous. This in turn should lead us to tolerate a significant degree of risk in order to reduce global temperatures. Indeed, by improving the welfare of (disproportionately poor) hot regions of the planet, at a slight expense to (disproportionately wealthy) cold ones, solar geoengineering has the potential to greatly ease global inequality. One attempt to model this impact found that it could reduce economic inequality by 25 percent at the global level, roughly similar to the income compression achieved within the U.S. during the four decades following the New Deal.
None of this means Joe Biden should dispatch a fleet of sulfur-spewing planes to the stratosphere tomorrow. First, we need better information about how to optimize such a program. We need to know which aerosols will reflect sunlight most effectively, and at the smallest possible cost to air quality. We need to understand how to space out aerosols in a manner that will alter weather patterns in a minimally disruptive and inequitable way. Notably, there is reason to think that such a distribution would be possible to achieve. One early study identified a deployment strategy that would appear to bring all of the world’s regions closer to their preindustrial levels of rainfall and temperature. In any case, the pro-solar-engineering think tank SilverLining estimates that a $2.6 billion annual investment into solar-engineering research would be sufficient to secure confident answers to the relevant policy questions.
Once we do have adequate insight into such matters, we should be able to execute a solar-radiation management policy with little difficulty. This is the singular virtue of aerosol injection, relative to trying to paint 2 percent of the Earth’s surface white or other somewhat novel schemes for cooling global temperatures. According to Keith, to reduce global temperatures by one Celsius degree via solar geoengineering, we would just need to send roughly 100 high-altitude aircraft into the stratosphere and have them release a little less than 2 million tons of sulfur. (For context, we currently, unintentionally generate roughly 40 million tons of sulfur by burning fossil fuels each year.)
As Ryan Cooper notes in Heatmap, the annual cost of such an endeavor is likely to be measured in the tens of billions. That isn’t nothing. But it’s also a small fraction of the Pentagon budget.
Ideally, a solar-geoengineering scheme would be formulated through multilateral global institutions and secure input and buy-in from all the world’s nations. Nonetheless, one of the policy’s virtues is that it provides the U.S. government with a lever for temporarily halting (or reversing) global warming, irrespective of what other nations do. Ultimately, the trajectory of future emissions will primarily be determined by decisions made in China, India, and other industrializing countries, which will be responsible for the lion’s share of CO2 emitted this century. Decarbonization in those nations is a precondition for achieving climate stability. But if China phases out fossil fuels at a slower than promised pace, solar geoengineering makes it possible for the U.S. (or any other sufficiently wealthy and technologically advanced nation) to single-handedly buy the world more time.
Geoengineering is a complement to decarbonization, not a substitute for it. To continue saturating the atmosphere with greenhouse gasses, while seeking to offset the temperature impact through aerosols, would be insane. Such a course of action would leave the world vulnerable to experiencing an abrupt surge in global temperatures should humanity ever fail to replenish the stratosphere’s aerosols in due time. Further, the more sulfur dioxide we need to pump into air, the more hazardous the potential side effects.
But if we want to reverse the climate change that we’ve already experienced, and safeguard vulnerable populations from the consequences of our historical carbon emissions, then there is no alternative to blotting out the sun. Or at least, there will not be until we figure out a way to paint the entire United States white.