Fixing our collective meat problem is one of the trickiest challenges in addressing climate change—and for some baffling reason, the world seems intent on making the task even harder.

The latest example occurred last week, when Florida governor Ron DeSantis signed a law banning the production, sale, and transportation of cultured meat across the Sunshine State. 

“Florida is fighting back against the global elite’s plan to force the world to eat meat grown in a petri dish or bugs to achieve their authoritarian goals,” DeSantis seethed in a statement.

Alternative meat and animal products—be they lab-grown or plant-based—offer a far more sustainable path to mass-producing protein than raising animals for milk or slaughter. Yet again and again, politicians, dietitians, and even the press continue to devise ways to portray these products as controversial, suspect, or substandard. No matter how good they taste or how much they might reduce greenhouse-gas emissions, there’s always some new obstacle standing in the way—in this case, Governor DeSantis, wearing a not-at-all-uncomfortable smile.  

The new law clearly has nothing to do with the creeping threat of authoritarianism (though for more on that, do check out his administration’s crusade to ban books about gay penguins). First and foremost it is an act of political pandering, a way to coddle Florida’s sizable cattle industry, which he goes on to mention in the statement.

Cultured meat is seen as a threat to the livestock industry because animals are only minimally involved in its production. Companies grow cells originally extracted from animals in a nutrient broth and then form them into nuggets, patties or fillets. The US Department of Agriculture has already given its blessing to two companies, Upside Foods and Good Meat, to begin selling cultured chicken products to consumers. Israel recently became the first nation to sign off on a beef version.

It’s still hard to say if cultured meat will get good enough and cheap enough anytime soon to meaningfully reduce our dependence on cattle, chicken, pigs, sheep, goats, and other animals for our protein and our dining pleasure. And it’s sure to take years before we can produce it in ways that generate significantly lower emissions than standard livestock practices today.

But there are high hopes it could become a cleaner and less cruel way of producing meat, since it wouldn’t require all the land, food, and energy needed to raise, feed, slaughter, and process animals today. One study found that cultured meat could reduce emissions per kilogram of meat 92% by 2030, even if cattle farming also achieves substantial improvements.

Those sorts of gains are essential if we hope to ease the rising dangers of climate change, because meat, dairy, and cheese production are huge contributors to greenhouse-gas emissions.

DeSantis and politicians in other states that may follow suit, including Alabama and Tennessee, are raising the specter of mandated bug-eating and global-elite string-pulling to turn cultured meat into a cultural issue, and kill the industry in its infancy. 

But, again, it’s always something. I’ve heard a host of other arguments across the political spectrum directed against various alternative protein products, which also include plant-based burgers, cheeses, and milks, or even cricket-derived powders and meal bars. Apparently these meat and dairy alternatives shouldn’t be highly processed, mass-produced, or genetically engineered, nor should they ever be as unhealthy as their animal-based counterparts. 

In effect, we are setting up tests that almost no products can pass, when really all we should ask of alternative proteins is that they be safe, taste good, and cut climate pollution.

The meat of the matter

Here’s the problem. 

Livestock production generates more than 7 billion tons of carbon dioxide, making up 14.5% of the world’s overall climate emissions, according to the United Nations Food and Agriculture Organization.

Beef, milk, and cheese production are, by far, the biggest problems, representing some 65% of the sector’s emissions. We burn down carbon-dense forests to provide cows with lots of grazing land; then they return the favor by burping up staggering amounts of methane, one of the most powerful greenhouse gases. Florida’s cattle population alone, for example, could generate about 180 million pounds of methane every year, as calculated from standard per-animal emissions. 

In an earlier paper, the World Resources Institute noted that in the average US diet, beef contributed 3% of the calories but almost half the climate pollution from food production. (If you want to take a single action that could meaningfully ease your climate footprint, read that sentence again.)

The added challenge is that the world’s population is both growing and becoming richer, which means more people can afford more meat. 

There are ways to address some of the emissions from livestock production without cultured meat or plant-based burgers, including developing supplements that reduce methane burps and encouraging consumers to simply reduce meat consumption. Even just switching from beef to chicken can make a huge difference.

Let’s clear up one matter, though. I can’t imagine a politician in my lifetime, in the US or most of the world, proposing a ban on meat and expecting to survive the next election. So no, dear reader. No one’s coming for your rib eye. If there’s any attack on personal freedoms and economic liberty here, DeSantis is the one waging it by not allowing Floridians to choose for themselves what they want to eat.

But there is a real problem in need of solving. And the grand hope of companies like Beyond Meat, Upside Foods, Miyoko’s Creamery, and dozens of others is that we can develop meat, milk, and cheese alternatives that are akin to EVs: that is to say, products that are good enough to solve the problem without demanding any sacrifice from consumers or requiring government mandates. (Though subsidies always help.)

The good news is the world is making some real progress in developing substitutes that increasingly taste like, look like, and have (with apologies for the snooty term) the “mouthfeel” of the traditional versions, whether they’ve been developed from animal cells or plants. If they catch on and scale up, it could make a real dent in emissions—with the bonus of reducing animal suffering, environmental damage, and the spillover of animal disease into the human population.

The bad news is we can’t seem to take the wins when we get them. 

The blue cheese blues

For lunch last Friday, I swung by the Butcher’s Son Vegan Delicatessen & Bakery in Berkeley, California, and ordered a vegan Buffalo chicken sandwich with a blue cheese on the side that was developed by Climax Foods, also based in Berkeley.

Late last month, it emerged that the product had, improbably, clinched the cheese category in the blind taste tests of the prestigious Good Food awards, as the Washington Post revealed.

Let’s pause here to note that this is a stunning victory for vegan cheeses, a clear sign that we can use plants to produce top-notch artisanal products, indistinguishable even to the refined palates of expert gourmands. If a product is every bit as tasty and satisfying as the original but can be produced without milking methane-burping animals, that’s a big climate win.

But sadly, that’s not where the story ended.

After word leaked out that the blue cheese was a finalist, if not the winner, the Good Food Foundation seems to have added a rule that didn’t exist when the competition began but which disqualified Climax Blue, the Post reported.

I have no special insights into what unfolded behind the scenes. But it reads at least a little as if the competition concocted an excuse to dethrone a vegan cheese that had bested its animal counterparts and left traditionalists aghast. 

That victory might have done wonders to help promote acceptance of the Climax product, if not the wider category. But now the story is the controversy. And that’s a shame. Because the cheese is actually pretty good. 

I’m no professional foodie, but I do have a lifetime of expertise born of stubbornly refusing to eat any salad dressing other than blue cheese. In my own taste test, I can report it looked and tasted like mild blue cheese, which is all it needs to do.

A beef about burgers

Banning a product or changing a cheese contest’s rules after determining the winner are both bad enough. But the reaction to alternative proteins that has left me most befuddled is the media narrative that formed around the latest generation of plant-based burgers soon after they started getting popular a few years ago. Story after story would note, in the tone of a bold truth-teller revealing something new each time: Did you know these newfangled plant-based burgers aren’t actually all that much healthier than the meat variety? 

To which I would scream at my monitor: THAT WAS NEVER THE POINT!

The world has long been perfectly capable of producing plant-based burgers that are better for you, but the problem is that they tend to taste like plants. The actual innovation with the more recent options like Beyond Burger or Impossible Burger is that they look and taste like the real thing but can be produced with a dramatically smaller climate footprint.

That’s a big enough win in itself. 

If I were a health reporter, maybe I’d focus on these issues too. And if health is your personal priority, you should shop for a different plant-based patty (or I might recommend a nice salad, preferably with blue cheese dressing).

But speaking as a climate reporter, expecting a product to ease global warming, taste like a juicy burger, and also be low in salt, fat, and calories is absurd. You may as well ask a startup to conduct sorcery.

More important, making a plant-based burger healthier for us may also come at the cost of having it taste like a burger. Which would make it that much harder to win over consumers beyond the niche of vegetarians and thus have any meaningful impact on emissions. WHICH IS THE POINT!

It’s incredibly difficult to convince consumers to switch brands and change behaviors, even for a product as basic as toothpaste or toilet paper. Food is trickier still, because it’s deeply entwined with local culture, family traditions, festivals and celebrations. Whether we find a novel food product to be yummy or yucky is subjective and highly subject to suggestion. 

And so I’m ending with a plea. Let’s grant ourselves the best shot possible at solving one of the hardest, most urgent problems before us. Treat bans and political posturing with the ridicule they deserve. Reject the argument that any single product must, or can, solve all the problems related to food, health, and the environment.

Give these alternative foods a shot, afford them room to improve, and keep an open mind. 

Though it’s cool if you don’t want to try the crickets.

Eliminating carbon pollution from aviation is one of the most challenging parts of the climate puzzle, simply because large commercial airlines are too heavy and need too much power during takeoff for today’s batteries to do the job. 

But one way that companies and governments are striving to make some progress is through the use of various types of sustainable aviation fuels (SAFs), which are derived from non-petroleum sources and promise to be less polluting than standard jet fuel.

This week, the US announced a push to help its biggest commercial crop, corn, become a major feedstock for SAFs. 

Federal guidelines announced on April 30 provide a pathway for ethanol producers to earn SAF tax credits within the Inflation Reduction Act, President Biden’s signature climate law, when the fuel is produced from corn or soy grown on farms that adopt certain sustainable agricultural practices.

It’s a limited pilot program, since the subsidy itself expires at the end of this year. But it could set the template for programs in the future that may help ethanol producers generate more and more SAFs, as the nation strives to produce billions of gallons of those fuels per year by 2030. 

Consequently, the so-called Climate Smart Agricultural program has already sounded alarm bells among some observers, who fear that the federal government is both overestimating the emissions benefits of ethanol and assigning too much credit to the agricultural practices in question. Those include cover crops, no-till techniques that minimize soil disturbances, and use of “enhanced-efficiency fertilizers,” which are designed to increase uptake by plants and thus reduce runoff into the environment.

The IRA offers a tax credit of $1.25 per gallon for SAFs that are 50% lower in emissions than standard jet fuel, and as much as 50 cents per gallon more for sustainable fuels that are cleaner still. The new program can help corn- or soy-based ethanol meet that threshold when the source crops are produced using some or all of those agricultural practices.

Since the vast majority of US ethanol is produced from corn, let’s focus on the issues around that crop. To get technical, the program allows ethanol producers to subtract 10 grams of carbon dioxide per megajoule of energy, a measure of carbon intensity, from the life-cycle emissions of the fuel when it’s generated from corn produced with all three of the practices mentioned. That’s about an eighth to a tenth of the carbon intensity of gasoline.

Ethanol’s questionable climate footprint

Today, US-generated ethanol is mainly mixed with gasoline. But ethanol producers are eager to develop new markets for the product as electric vehicles make up a larger share of the cars and trucks on the road. Not surprisingly, then, industry trade groups applauded the announcement this week.

The first concern with the new program, however, is that the emissions benefits of corn-based ethanol have been hotly debated for decades.

Corn, like any plant that uses photosynthesis to produce food, sucks up carbon dioxide from the air. But using corn for fuel rather than food also creates pressure to clear more land for farming, a process that releases carbon dioxide from plants and soil. In addition, planting, fertilizing, and harvesting corn produce climate pollution as well, and the same is true of refining, distributing, and burning ethanol. 

For its analyses under the new program, the Treasury Department intends to use an updated version of the so-called GREET model to evaluate the life-cycle emissions of SAFs, which was developed by the Department of Energy’s Argonne National Lab. A 2021 study from the lab, relying on that model, concluded that US corn ethanol produced as much as 52% less greenhouse gas than gasoline. 

But some researchers and nonprofits have criticized the tool for accepting low estimates of the emissions impacts of land-use changes, among other issues. Other assessments of ethanol emissions have been far more damning.

A 2022 EPA analysis surveyed the findings from a variety of models that estimate the life-cycle emissions of corn-based ethanol and found that in seven out of 20 cases, they exceeded 80% of the climate pollution from gasoline and diesel.

Moreover, the three most recent estimates from those models found ethanol emissions surpassed even the higher-end estimates for gasoline or diesel, Alison Cullen, chair of the EPA’s science advisory board, noted in a 2023 letter to the administrator of the agency.

“Thus, corn starch ethanol may not meet the definition of a renewable fuel” under the federal law that mandates the use of biofuels in the market, she wrote. If so, it’s then well short of the 50% threshold required by the IRA, and some say it’s not clear that the farming practices laid out this week could close the gap.

Agricultural practices

Nikita Pavlenko, who leads the fuels team at the International Council on Clean Transportation, a nonprofit research group, asserted in an email that the climate-smart agricultural provisions “are extremely sloppy” and “are not substantiated.” 

He said the Department of Energy and Department of Agriculture especially “put their thumbs on the scale” on the question of land-use changes, using estimates of soy and corn emissions that were 33% to 55% lower than those produced for a program associated with the UN’s International Civil Aviation Organization.

He finds that ethanol sourced from farms using these agriculture practices will still come up short of the IRA’s 50% threshold, and that producers may have to take additional steps to curtail emissions, potentially including adding carbon capture and storage to ethanol facilities or running operations on renewables like wind or solar.

Freya Chay, a program lead at CarbonPlan, which evaluates the scientific integrity of carbon removal methods and other climate actions, says that these sorts of agricultural practices can provide important benefits, including improving soil health, reducing erosion, and lowering the cost of farming. But she and others have stressed that confidently determining when certain practices actually and durably increase carbon in soil is “exceedingly complex” and varies widely depending on soil type, local climate conditions, past practices, and other variables.

One recent study of no-till practices found that the carbon benefits quickly fade away over time and reach nearly zero in 14 years. If so, this technique would do little to help counter carbon emissions from fuel combustion, which can persist in the atmosphere for centuries or more.

“US policy has a long history of asking how to continue justifying investment in ethanol rather than taking a clear-eyed approach to evaluating whether or not ethanol helps us reach our climate goals,” Chay wrote in an email. “In this case, I think scrutiny is warranted around the choice to lean on agricultural practices with uncertain and variable benefits in a way that could unlock the next tranche of public funding for corn ethanol.”

There are many other paths for producing SAFs that are or could be less polluting than ethanol. For example, they can be made from animal fats, agriculture waste, forest trimmings, or non-food plants that grow on land unsuitable for commercial crops. Other companies are developing various types of synthetic fuels, including electrofuels produced by capturing carbon from plants or the air and then combining it with cleanly sourced hydrogen. 

But all these methods are much more expensive than extracting and refining fossil fuels, and most of the alternative fuels will still produce more emissions when they’re used than the amount that was pulled out of the atmosphere by the plants or processes in the first place. 

The best way to think of these fuels is arguably as a stopgap, a possible way to make some climate progress while smart people strive to develop and build fully emissions-free ways of quickly, safely, and reliably moving things and people around the globe.

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here.

Usually when we talk about climate change, the focus is squarely on the role that greenhouse-gas emissions play in driving up global temperatures, and rightly so. But another important, less-known phenomenon is also heating up the planet: reductions in other types of pollution.

In particular, the world’s power plants, factories, and ships are pumping much less sulfur dioxide into the air, thanks to an increasingly strict set of global pollution regulations. Sulfur dioxide creates aerosol particles in the atmosphere that can directly reflect sunlight back into space or act as the “condensation nuclei” around which cloud droplets form. More or thicker clouds, in turn, also cast away more sunlight. So when we clean up pollution, we also ease this cooling effect. 

Before we go any further, let me stress: cutting air pollution is smart public policy that has unequivocally saved lives and prevented terrible suffering. 

The fine particulate matter produced by burning coal, gas, wood, and other biomatter is responsible for millions of premature deaths every year through cardiovascular disease, respiratory illnesses, and various forms of cancer, studies consistently show. Sulfur dioxide causes asthma and other respiratory problems, contributes to acid rain, and depletes the protective ozone layer. 

Air pollution is killing millions of people per year.

It would be a vastly better outcome for humanity if we could cut it rapidly, despite the resulting warming impact on the climate. https://t.co/JYWAWwVtiG

— Zeke Hausfather (@hausfath) April 8, 2024

But as the world rapidly warms, it’s critical to understand the impact of pollution-fighting regulations on the global thermostat as well. Scientists have baked the drop-off of this cooling effect into net warming projections for the coming decades, but they’re also striving to obtain a clearer picture of just how big a role declining pollution will play.

A new study found that reductions in emissions of sulfur dioxide and other pollutants are responsible for about 38%, as a middle estimate, of the increased “radiative forcing” observed on the planet between 2001 and 2019. 

An increase in radiative forcing means that more energy is entering the atmosphere than leaving it, as Kerry Emanuel, a professor of atmospheric science at MIT, lays out in a handy explainer here. As that balance has shifted in recent decades, the difference has been absorbed by the oceans and atmosphere, which is what is warming up the planet. 

The remainder of the increase is “mainly” attributable to continued rising emissions of heat-trapping greenhouse gases, says Øivind Hodnebrog, a researcher at the Center for International Climate and Environment Research in Norway and lead author of the paper, which relied on climate models, sea-surface temperature readings, and satellite observations.

The study underscores the fact that as carbon dioxide, methane, and other gases continue to drive up temperature​​s, parallel reductions in air pollution are revealing more of that additional warming, says Zeke Hausfather, a scientist at the independent research organization Berkeley Earth. And it’s happening at a point when, by most accounts, global warming is about to begin accelerating or has already started to do so. (There’s ongoing debate over whether researchers can yet detect that acceleration and whether the world is now warming faster than researchers had expected.)

Because of the cutoff date, the study did not capture a more recent contributor to these trends. Starting in 2020, under new regulations from the International Maritime Organization, commercial shipping vessels have also had to steeply reduce the sulfur content in fuels. Studies have already detected a decrease in the formation of “ship tracks,” or the lines of clouds that often form above busy shipping routes. 

Again, this is a good thing in the most important way: maritime pollution alone is responsible for tens of thousands of early deaths every year. But even so, I have seen and heard of suggestions that perhaps we should slow down or alter the implementation of some of these pollution policies, given the declining cooling effect.

A 2013 study explored one way to potentially balance the harms and benefits. The researchers simulated a scenario in which the maritime industry would be required to use very low-sulfur fuels around coastlines, where the pollution has the biggest effect on mortality and health. But then the vessels would double the fuel’s sulfur content when crossing the open ocean. 

In that hypothetical world, the cooling effect was a bit stronger and premature deaths declined by 69% with respect to figures at the time, delivering a considerable public health improvement. But notably, under a scenario in which low-sulfur fuels were required across the board, mortality declined by 96%, a difference of more than 13,000 preventable deaths every year.

Now that the rules are in place and the industry is running on low-sulfur fuels, intentionally reintroducing pollution over the oceans would be a far more controversial matter.

While society basically accepted for well over a century that ships were inadvertently emitting sulfur dioxide into the air, flipping those emissions back on for the purpose of easing global warming would amount to a form of solar geoengineering, a deliberate effort to tweak the climate system.

Many think such planetary interventions are far too powerful and unpredictable for us to muck around with. And to be sure, this particular approach would be one of the more ineffective, dangerous, and expensive ways to carry out solar geoengineering, if the world ever decided it should be done at all. The far more commonly studied concept is emitting sulfur dioxide high in the stratosphere, where it would persist for longer and, as a bonus, not be inhaled by humans. 

On an episode of the Energy vs. Climate podcast last fall, David Keith, a professor at the University of Chicago who has closely studied the topic, said that it may be possible to slowly implement solar geoengineering in the stratosphere as a means of balancing out the reduced cooling occurring from sulfur dioxide emissions in the troposphere.

“The kind of solar geoengineering ideas that people are talking about seriously would be a thin wedge that would, for example, start replacing what was happening with the added warming we have from unmasking the aerosol cooling from shipping,” he said. 

Positioning the use of solar geoengineering as a means of merely replacing a cruder form that the world was shutting down offers a somewhat different mental framing for the concept—though certainly not one that would address all the deep concerns and fierce criticisms.

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Back in 2018, I wrote a piece about the maritime rules that were then in the works and the likelihood that they would fuel additional global warming, noting that we were “about to kill a massive, unintentional” experiment in solar geoengineering.

Another thing

Speaking of the concerns about solar geoengineering, late last week I published a deep dive into Harvard’s unsuccessful, decade-long effort to launch a high-altitude balloon to conduct a tiny experiment in the stratosphere. I asked a handful of people who were involved in the project or followed it closely for their insights into what unfolded, the lessons that can be drawn from the episode—and their thoughts on what it means for geoengineering research moving forward.

Keeping up with Climate 

Yup, as the industry predicted (and common sense would suggest), this week’s solar eclipse dramatically cut solar power production across North America. But for the most part, grid operators were able to manage their systems smoothly, minus a few price spikes, thanks in part to a steady buildout of battery banks and the availability of other sources like natural gas and hydropower. (Heatmap)

There’s been a pile-up of bad news for Tesla in recent days. First, the company badly missed analyst expectations for vehicle deliveries during the first quarter. Then, Reuters reported that the EV giant has canceled plans for a low-cost, mass-market car. That may have something to do with the move to “prioritize the development of a robotaxi,” which the Wall Street Journal then wrote about. Over on X, Elon Musk denied the Reuters story, sort of—posting that “Reuters is lying (again).” But there’s a growing sense that his transformation into a “far-right activist” is exacting an increasingly high cost on his personal and business brands. (Wall Street Journal)

In a landmark ruling this week, the European Court of Human Rights determined that by not taking adequate steps to address the dangers of climate change, including increasingly severe heat waves that put the elderly at particular risk, Switzerland had violated the human rights of a group of older Swiss women who had brought a case against the country. Legal experts say the ruling creates a precedent that could unleash many similar cases across Europe. (The Guardian)

In late March of 2017, at a small summit in Washington, DC, two Harvard professors, David Keith and Frank Keutsch, laid out plans to conduct what would have been the first solar geoengineering experiment in the stratosphere.

Instead, it became the focal point of a fierce public debate over whether it’s okay to research such a controversial topic at all.

The basic concept behind solar geoengineering is that by spraying certain particles high above the planet, humans could reflect some amount of sunlight back into space as a means of counteracting climate change. 

The Harvard researchers hoped to launch a high-altitude balloon, tethered to a gondola equipped with propellers and sensors, from a site in Tucson, Arizona, as early as the following year. After initial equipment tests, the plan was to use the aircraft to spray a few kilograms of material about 20 kilometers (12.4 miles) above Earth and then fly back through the plume to measure how reflective the particles were, how readily they dispersed, and other variables. 

But the initial launch didn’t happen the following year, nor the next, the next, or the next—not in Tucson, nor at a subsequently announced site in Sweden. Complications with balloon vendors, the onset of the covid pandemic, and challenges in finalizing decisions between the team, its advisory committee, and other parties at Harvard kept delaying the project—and then fervent critiques from environmental groups, a Northern European Indigenous organization, and other opponents finally scuttled the team’s plans.

Critics, including some climate scientists, have argued that an intervention that could tweak the entire planet’s climate system is too dangerous to study in the real world, because it’s too dangerous to ever use. They fear that deploying such a powerful tool would inevitably cause unpredictable and dangerous side effects, and that the world’s countries could never work together to use it in a safe, equitable, and responsible way.

These opponents believe that even discussing and researching the possibility of such climate interventions eases pressures to rapidly cut greenhouse-gas emissions and increases the likelihood that a rogue actor or solitary nation will one day begin spraying materials into the stratosphere without any broader consensus. Unilateral use of the tool, with its potentially calamitous consequences for some regions, could set nations on a collision course toward violent conflicts.

Harvard’s single, small balloon experiment, known as the Stratospheric Controlled Perturbation Experiment, or SCoPEx, came to represent all of these fears—and, in the end, it was more than the researchers were prepared to take on. Last month, a decade after the project was first proposed in a research paper, Harvard officially announced the project’s termination, as first reported by MIT Technology Review.

“The experiment became this proxy for a kind of debate about whether solar geoengineering research should move forward,” Keith says. “And that’s, I think, the ultimate reason why Frank and I decided to pull the plug. There’s no way, given that weight that SCoPEx had come to hold, it made sense to move forward.”

I’ve been writing about solar geoengineering for more than a decade. I reported on the conference in 2017, and I continued to cover the team’s evolving plans over the following years. So the cancellation of the project left me puzzling over why it failed, and what that failure says about the latitude that researchers have to explore such a controversial subject.

In recent days, I asked a handful of people who were involved in the project or followed it closely for their insights and thoughts on what unfolded, what lessons can be drawn from the episode—and what it means for geoengineering research moving forward.

Few of the people I spoke with believe it spells the end of outdoor experiments in solar geoengineering, but some argue that it should—and others believe any future proposals should proceed in a very different way if researchers hope to avoid the same fate.

A short history of SCoPEx

Nature offered the inspiration for solar geoengineering: massive volcanic eruptions in the past have cooled global temperatures by emitting vast amounts of sulfur dioxide, which eventually form sulfuric acid aerosols that reflect away solar radiation. 

The 1991 eruption of Mount Pinatubo in the Philippines, for instance, blasted nearly 20 million tons of sulfur dioxide into the stratosphere, cooling global surface temperatures by around 0.5 °C for months.

But one concern about relying on the gas for geoengineering is that sulfuric acid also depletes the ozone layer, which shields life on Earth from harmful ultraviolet light. So some researchers, including Keith, have used computer models to explore whether we could reduce or even reverse that side effect by replacing sulfur dioxide with other substances, including diamond dust, alumina, or calcium carbonate. 

The SCoPEx researchers discussed the possibility of releasing several materials over a series of flights, including sulfuric acid, but they mainly emphasized calcium carbonate.

They hoped that the data from the launches could refine the accuracy of geoengineering simulations and improve our understanding of the technology’s potential benefits and risks.

“You have to go measure things in the real world, because nature surprises you,” Keith said at that conference in 2017.

He has continually stressed that the amount of material involved would represent a small fraction of the particulate pollution already emitted by planes, and that doing the same experiment for any other scientific purpose wouldn’t have raised an eyebrow.

But theirs became a lightning rod. In their effort to be upfront and transparent about their plans, Keith believes, they set off a self-reinforcing cycle of overheated press coverage and fierce attacks from critics, all of which inflated public concerns about what he contends was an ordinary experiment with negligible environmental impact. 

The team’s initial hopes for launching a balloon in Arizona in 2018 never came to fruition because the balloon vendor they were working with, World View, stopped launching payloads of the necessary weight, Keith says. (The company didn’t respond to an inquiry before press time.)

But the researchers continued to develop the equipment and aircraft in the labs at Harvard, and the university set up an oversight panel that began reviewing the team’s plans and developing guidelines for engaging with the public.

Eventually, the researchers shifted their focus to Sweden, where they began planning a launch to test the aircraft’s equipment, working with the Swedish Space Corporation. The balloon was set to lift off from the Esrange Space Center in Kiruna in the summer of 2021.

The aircraft would not have released any materials during that launch. But anti-geoengineering groups, environmental organizations, Swedish environmental activist Greta Thunberg, the Saami Council (which represents the Indigenous Saami peoples of Northern Europe), and the board of the Royal Swedish Academy of Sciences all criticized the plan, putting pressure on the aerospace company, the research team, and the advisors to halt the launch. 

Solar geoengineering “is a technology that entails risks of catastrophic consequences, including the impact of uncontrolled termination, and irreversible sociopolitical effects that could compromise the world’s necessary efforts to achieve zero-carbon societies,” the Saami Council wrote in a letter to the advisory committee. “There are therefore no acceptable reasons for allowing the SCoPEx project to be conducted either in Sweden or elsewhere.”

In response, the advisory committee recommended that the researchers delay their plans until they had conducted conversations about the project with the public and concerned parties. In late March of 2021, the team and the company agreed to stand down.

The project never regained traction from there.

Last spring, Keith moved to the University of Chicago, where he now leads the Climate Systems Engineering initiative, a multidisciplinary research effort dedicated to improving understanding of solar geoengineering, carbon removal, and other interventions that could counteract the effects of climate change.

A few months later, the research team informed the advisory committee that it had “suspended work” on the experiment. Then, last month, Keutsch officially confirmed he’s no longer pursuing the project.

“I felt that it was time to focus on other innovative research avenues in the incredibly important field of [solar radiation modification] that promise impactful results,” he said in an email.

Too dangerous to study

Plenty of observers are pleased with the outcome. 

Hundreds of researchers from a variety of disciplines have signed an open letter calling for an “International Non-Use Agreement on Solar Geoengineering,” stating that governments should commit to “ban outdoor experiments of solar geoengineering.”

Jennie Stephens, a professor of sustainability science and policy at Northeastern University, was one of the letter’s signatories. She argues that the SCoPEx experiment was particularly dangerous, because the funding, attention, and prestige of Harvard conferred legitimacy on planet-scale interventions that, to her mind, can never be safely governed or controlled.

She argues that even if the researchers have the best of intentions, solar geoengineering would ultimately be deployed by people or nations with money and power in ways that most benefit their interests, even if it meant disastrous consequences for other areas. Some research, for instance, suggests that solar geoengineering could significantly reduce rainfall in certain areas and might reduce the yields of some staple crops. While one block of nations might decide to use geoengineering to ease heat waves, what if that reduced the summer monsoons and the food supplies across parts of India or West Africa?

“There’s no way to even imagine deploying it on a global scale so that everybody would benefit,” she says. “Some people would be screwed, and some people may have reduced suffering. So it’s creating one more mechanism by which to interfere with the Earth systems and then privilege some and disadvantage others.”

Openness

But many believe it’s essential to learn more about the role that solar geoengineering could play in easing global warming, and whether the side effects could be moderated. There’s a simple reason: if it does work well, it could save many lives and ease suffering as climate change accelerates. 

For these observers, then, the question is: What lessons can be drawn to ensure that other experiments can go forward? And perhaps of equal importance: What lessons shouldn’t be drawn from SCoPEx?

Some researchers in the field fear that the broader takeaway from the termination of the project will be that the Harvard team chose to be too open about its intentions.

The “organized opposition to even the concept of outdoor experiments” makes it difficult for other research groups to pursue similar work and “may increase the probability of rogue actors,” says Michael Gerrard, faculty director of Columbia University’s Sabin Center for Climate Change Law, who served on the advisory committee. He notes that such activities are largely unregulated.

Immediately following the news that Harvard was no longer pursuing the project, several figures in the cleantech industry took to social media to say that people could, or should, release particles into the stratosphere on their own.

While the Harvard team’s public plans were going nowhere, several other individuals claimed to have simply started launching stratosphere-bound balloons without any announcements in advance. They include the CEO of Make Sunsets, a venture-backed geoengineering startup, as well as Andrew Lockley, an independent researcher in the UK. 

Meanwhile, earlier this week, a University of Washington-led research group conducted a small experiment in marine cloud brightening, another form of solar geoengineering, on a decommissioned aircraft carrier anchored off the coast of Alameda, California, according to the New York Times. The team “kept the details tightly held, concerned that critics would try to stop them,” the newspaper reported.

Keith himself is “strongly opposed” to doing anything “rogue,” in the sense of illegal, or to conducting any such research in this field outside of the normal scientific process. And he says that “not being open at all” isn’t the right strategy.  

But he is wrestling with how up-front researchers should be. The level of early notice and transparency they strived for “maybe really doesn’t work in a conflictual environment,” he observes. “So maybe we should have been significantly less open and had a few limited sets of checks.”

Sikina Jinnah, a professor of environmental studies at the University of California, Santa Cruz, who joined the project’s advisory committee after the Sweden decision, draws the opposite lesson about transparency and engagement. 

She says that the Harvard team never got to the point of engaging with the public about its plans in any formal way in Sweden, and she stresses that such conversations should begin much earlier in the process. (This was also one of the main conclusions in the committees’ final report on the experiment, which was released last month.)

“Early engagement, I think, is one of the big take-home lessons,” she says. “And not just sort of cursory ‘giving a public talk’ kind of engagement, but really moving to iterative engagement with communities about their concerns, about questions they may be interested in, and really starting to reframe that kind of engagement process as one that’s not detrimental to the research effort but can actually enhance research and enrich it in ways that are socially beneficial.”

Scientific merit

Other observers believe there was a more basic problem with SCoPEx.

“Most of the scientists in the field didn’t feel like it was a particularly essential experiment,” said Douglas MacMartin, an associate professor at Cornell University who focuses on solar geoengineering, in an email.

As a result, there wasn’t a rush to defend it, he added.

MacMartin explained that the project was more focused on studying alternative aerosols, mainly calcium carbonate, rather than addressing unknowns concerning the substance that most people think would be used: sulfur dioxide. 

That’s because scientists know much more about its overall effects and can model them more accurately, since volcanoes already add the gas to the stratosphere naturally. Climate models also suggest that the impact on ozone would be minimal “and thus not worrisome enough to justify turning to a less-well-understood material,” he said.

Alan Robock, a climate scientist at Rutgers who has highlighted the potential risks of geoengineering, echoed this concern. 

“I don’t think this project ever had a good science question,” he says. “I think it was more driven by wanting to build something, the engineering.”

MacMartin says the crucial starting questions for experiments in this field are what gaps in our understanding such research could fill and whether that information would help to inform decisions about geoengineering. And it’s the pursuit of those answers that should be communicated as the rationale to the public.

But, he says, too often the SCoPEx researchers articulated their case for the work along the lines of, “Hey, this is small—you should let us do it because we want to.”

In an email, Keutsch noted that one of the things they hoped to better understand through the experiment was how plumes of injected particles spread out and mix in the stratosphere. In addition, Keith noted that they did discuss releasing and studying sulfuric acid as well, though they tended to talk more about calcium carbonate.

Broader scientific program

Another concern about the project from early on was that it was a one-off, privately funded experiment, moving ahead outside of any broader, government-backed research program. (Funding came from grants that Harvard provided the researchers as new professors and through the university’s Solar Geoengineering Research Program, which has raised money from the Alfred P. Sloan Foundation, the Hewlett Foundation, the Pritzker Innovation Fund, and other groups and individuals.) For less touchy subjects, such an experiment might be funded and overseen through a federal scientific body like the US National Science Foundation. 

That meant the university had to set up an advisory board if the institution wanted standard scientific oversight—and it meant that that committee had to craft its own rules for how such experiments should proceed, even as the researchers were taking steps toward an initial launch to test out their hardware.

Given the sensitivity of the topic, some observers believe that outdoor solar geoengineering experiments should only proceed through broader, public research programs involving scientific bodies with established practices for evaluating scientific merit, ethics, and environmental impact. Ideally, such programs would include “society-wide engagement,” tapping a variety of experts to impartially inform significant portions of the public about such interventions, explore their areas of concern, and, crucially, use that input to inform the design of the research program, says Holly Buck, an environmental social scientist at the University at Buffalo and author of After Geoengineering.

“Unless government is convening a serious engagement process where they are going to incorporate what they hear into policy in this area, I would expect any sort of outdoor experiment to meet a similar kind of resistance,” she said in an email.

Several nations have set up small-scale research efforts in the field, including the US and China. But a comprehensive program of this sort would require far more funding than has been allocated to date. A 2021 National Academies report recommended that the US government establish a cross-agency research program in solar geoengineering, backed by $100 million to $200 million over a five-year period. 

Future experiments 

Keith himself owns up to several mistakes in the research effort, including failing to anticipate that opponents would raise concerns over the basic hardware test in Sweden. He also says the team was wrong to move ahead without having a public engagement plan in place. The public failure of SCoPEx, he believes, will probably make it more difficult for other experiments in the stratosphere to go forward.

“Which is really sad,” he says. “And I apologize, and it’s a failure.”

But he also says there is still room for other groups to pursue outdoor experiments, and he believes the odds are strong that someone will.

Indeed, there are numerous indicators of growing interest in researching this field and providing funding for it. As noted, the US government is developing a research program. The Environmental Defense Fund is considering supporting scientists in the area and recently held a meeting to discuss guardrails that should govern such work. And a number of major philanthropies that haven’t supported the field in the past are in advanced discussions to provide funding to research groups, sources tell MIT Technology Review.

Meanwhile, under Keith, the University of Chicago is working to hire 10 faculty researchers in this area.

He says he wouldn’t look to lead an outdoor experiment himself at this point, but he does hope that people working with him at the Climate Systems Engineering Initiative would, if it could offer insights into the scientific questions they’re exploring. 

“I absolutely want to see experiments happen from the University of Chicago,” he says.

Harvard researchers have ceased a long-running effort to conduct a small geoengineering experiment in the stratosphere, following repeated delays and public criticism.

In a university statement released on March 18, Frank Keutsch, the principal investigator on the project, said he is “no longer pursuing the experiment.”

The basic concept behind solar geoengineering is that the world might be able to counteract global warming by spraying tiny particles in the atmosphere that could scatter sunlight. 

The plan for the Harvard experiments was to launch a high-altitude balloon, equipped with propellers and sensors, that could release a few kilograms of calcium carbonate, sulfuric acid or other materials high above the planet. It would then turn around and fly through the plume to measure how widely the particles disperse, how much sunlight they reflect and other variables. The aircraft will now be repurposed for stratospheric research unrelated to solar geoengineering, according to the statement.

The vast majority of solar geoengineering research to date has been carried out in labs or computer models. The so-called stratospheric controlled perturbation experiment (SCoPEx) was expected to be the first such scientific effort conducted in the stratosphere. But it proved controversial from the start and, in the end, others may have beaten them across the line of deliberately releasing reflective materials into that layer of the atmosphere. (The stratosphere stretches from approximately 10 to 50 kilometers above the ground.) 

Last spring, one of the main scientists on the project, David Keith, relocated to the University of Chicago, where he is leading the Climate Systems Engineering initiative. The new research group will explore various approaches to solar geoengineering, as well as carbon dioxide removal and regional climate interventions, such as efforts to shore up glaciers. 

That summer, the research team informed its advisory committee that it had “suspended work” on the experiment. But it stayed in limbo for months. No final decision on the project’s fate had been made as of early October, Harvard professor Daniel Schrag, who serves on the advisory committee of the university’s broader Solar Geoengineering Research Program, told MIT Technology Review at the time.

Proponents of solar geoengineering research argue we should investigate the concept because it may significantly reduce the dangers of climate change. Further research could help scientists better understand the potential benefits, risks and tradeoffs between various approaches. 

But critics argue that even studying the possibility of solar geoengineering eases the societal pressure to cut greenhouse gas emissions. They also fear such research could create a slippery slope that increases the odds that nations or rogue actors will one day deploy it, despite the possibility of dangerous side-effects, including decreasing precipitation and agricultural output in some parts of the world.

Keith and other scientists laid out the blueprint of the experiment in a paper a decade ago. Then in 2017, he and Keutsch announced they hoped to carry it out, by launching balloons from a site in Tucson, Arizona as early as the following year.

But the project switched locations several times. Most recently, the team hoped to launch a balloon to test out the aircraft’s hardware from the Esrange Space Center in Kiruna, Sweden in the summer of 2021. But those plans were canceled on the recommendation of the project’s advisory committee, which determined the researchers should hold discussions with the public ahead of any flights. The effort was also heavily criticized by the Saami Council, which represents the indigenous Saami peoples’ groups in Sweden and neighboring regions, as well as environmental groups and other organizations, who argued it’s too dangerous a tool to use. 

Solar geoengineering “is a technology that entails risks of catastrophic consequences, including the impact of uncontrolled termination, and irreversible sociopolitical effects that could compromise the world’s necessary efforts to achieve zero-carbon societies,” the group wrote in a letter to the advisory committee. “There are therefore no acceptable reasons for allowing the SCoPEx project to be conducted either in Sweden or elsewhere.”

When asked why he decided to stop work on the experiment, and if it had anything to do with the public pushback or delays, Keutsch replied via email that he “learned important lessons about governance and engagement throughout the course of this project.”

“The field of [solar radiation management] has undergone a significant transformation in the last few years, expanding the community and opening new doors for research and collaboration,” he added. “I felt that it was time to focus on other innovative research avenues in the incredibly important field of SRM that promise impactful results.”

Amid the delays to the Harvard project, other groups have forged ahead with their own geoengineering-related efforts. The controversial venture-backed startup, Make Sunsets, has repeatedly launched weather balloons filled with a few grams of sulfur dioxide that it claims likely burst in the stratosphere. Meanwhile, an independent researcher in the UK, Andrew Lockley, says he carried out several balloon launches, including a September 2022 flight that burst about 15 miles above the Earth and could have released around 400 grams of sulfur dioxide.

Despite the public controversy, the SCoPEx researchers earned high marks among some in the field for striving to carry out the field effort in a small-scale, controlled, transparent way, setting down clear research objectives and creating an independent advisory committee to review the proposals. 

Gernot Wagner, a climate economist at Columbia Business School and the former executive director of Harvard’s Solar Geoengineering Research Program, said in an email that the cancellation of the project was “unfortunate,” as it had taken on larger significance in the field. 

He stressed that the effort “widened the operating space for other, younger researchers to look into this important topic.” In addition, by publishing the plans in a peer-reviewed journal and operating transparently, the group “set a standard of sorts for responsible research in this area,” he added.

“Responsible researchers deciding not to conduct this kind of research, meanwhile, gives ample room for irresponsible actors with all sorts of crazy ideas,” Wagner said.

Harvard will continue to study geoengineering through the Solar Geoengineering Research Program, a multidisciplinary research effort set up in 2017 with funding from Microsoft cofounder Bill Gates, the Hewlett Foundation, the Alfred P. Sloan Foundation and other organizations and individuals. Other current or former projects there include a lab study of other materials that could potentially be used for solar geoengineering and an effort to identify and address some of the larger challenges in governing such tools. 

Also on Monday, the project’s advisory committee released a report to highlight the approach it developed to oversee the project and the key lessons learned, in the hope of informing future geoengineering research experiments. It stressed the need to engage with the public early on, to listen to their concerns, and to develop a plan to respond to them.

A handful of studies have concluded that making minor adjustments to the routes of a small fraction of airplane flights could meaningfully reduce global warming. Now a new paper finds that these changes could be pretty cheap to pull off as well.

The common climate concern when it comes to airlines is that planes produce a lot of carbon dioxide emissions as they burn fuel. But jets also release heat, water vapor, and particulate matter that can produce thin clouds in the sky, known as “contrails,” in particularly cold, humid, icy parts of the atmosphere.

When numerous flights pass through such areas, these condensation trails can form cirrus clouds that absorb radiation escaping from the surface, acting as blankets floating above the Earth. 

This cirrus-forming phenomenon could account for around 35% of aviation’s total contribution to climate change—or about 1% to 2% of overall global warming, according to some estimates.

A small fraction of overall flights, between 2% and 10%, create about 80% of the contrails. So the growing hope is that simply rerouting those flights could significantly reduce the effect, presenting a potentially high leverage, low cost and fast way of easing warming. 

Last summer, Breakthrough Energy, Google Research, and American Airlines announced some promising results from a research collaboration, as first reported in the New York Times. They employed satellite imagery, weather data, software models, and AI prediction tools to steer pilots over or under areas where their planes would be likely to produce contrails. American Airlines used these tools in 70 test flights over six months, and subsequent satellite data indicated that they reduced the total length of contrails by 54%, relative to flights that weren’t rerouted.

There would, of course, be costs to implementing such a strategy. It generally requires more fuel to steer clear of these areas, which also means the flights would produce more greenhouse-gas emissions (more on that wrinkle in a moment).

More fuel also means greater expenses, and airlines aren’t likely to voluntarily implement such measures if it’s not relatively affordable. 

A new study published in Environmental Research: Infrastructure and Sustainability explored this issue by coupling commercial tools for optimizing flight trajectories with models that simulated nearly 85,000 American Airlines flights, both domestic and international, under various weather conditions last summer and this winter.

In those simulations, the researchers found that reducing the warming effect of contrails by 73% increased fuel costs by just 0.11% and overall costs by 0.08%, when averaged across those tens of thousands of flights. (Only about 14% of the flights needed to be adjusted to avoid forming warming contrails in the simulations.)

“Obviously there’s a trade-off between added fuel and reductions in harmful contrails; that’s real, and it’s one of the biggest challenges to this climate solution,” says Marc Shapiro, a coauthor of the paper and director of the contrails team at Breakthrough Energy, an organization founded by Bill Gates to spur innovation in clean energy and address climate change. “But what we’re showing in this paper is that the added fuel burn is a lot less than we expected.”

Airlines could also use such a commercial trajectory tool to make decisions that balance their financial and climate goals, he says. For example, they could allow some contrail-forming flights when the cost of adjusting the routes would be especially high.

Other research groups and airlines are also evaluating this concept through projects, including a collaboration between Delta and MIT’s Department of Aeronautics and Astronautics. (MIT Technology Review is owned by MIT but is editorially independent.)

There are other approaches to reducing contrail formation, including switching to different types of fuels or continuing to develop more capable electric or hydrogen-powered aircraft. 

But the studies to date suggest that rerouting flights could be one of the simplest ways of substantially reducing contrail-related warming. 

“So far, it’s looking very promising that it will be the cheapest, fastest way to reduce the climate impacts of aviation,” says Steven Barrett, head of the MIT department. 

Finding any way to make near-term progress on aviation is all the more important since it’s still likely to take a long time to develop and implement scalable, affordable ways of addressing the emissions from heavy fuel use, he adds.

But it will take more modeling studies and real-world experiments to demonstrate that “contrails avoidance,” as the approach is known, works as effectively as hoped.

For one thing, Barrett says, researchers still need to test, refine, and engineer systems that can reliably predict, with enough time to reroute planes, when and where contrails will form—all amid shifting weather conditions.

There are also some thorny complications that still need to be resolved, like the fact that cirrus clouds can also reduce warming by reflecting away short-wave radiation from the sun.

The loss of this cooling effect would have to be tallied into any calculation of the net benefit—or, perhaps, avoided. For instance, Shapiro says the initial strategy might be to reroute flights only during the early evening and night, which would eliminate the sunlight-reflecting complication. 

In addition, any decreased warming from contrail avoidance must more than offset the added warming from increased greenhouse-gas pollution. This becomes a trickier question when we weigh whether we care more about short-term or long-term warming: not producing contrails delivers an immediate benefit, but any added carbon dioxide can take decades to exert its full warming effect and may persist for hundreds to thousands of years.

The new study, at least, found that even when additional greenhouse gases are taken into account, reducing contrails cuts net warming over both a 20-year and a 100-year timeline, though less so in the latter scenario. But that, too, would need to be evaluated further through additional studies.

Yet another open question is whether airspace constraints and traffic bottlenecks might limit airlines’ ability to regularly reroute the necessary flights.

As a next step, Breakthrough Energy hopes to work with airlines to explore some of these questions by scaling up real-world flights and observations. 

But even if subsequent studies do continue to indicate that this is a fast, affordable way to ease warming, it’s still not clear whether airlines will do it if regulators don’t force them to. While the fuel costs to make this work may be tiny in percentage terms, they could add up quickly across a fleet and over time.

Still, the study’s authors assert that they’ve shown contrail avoidance could deliver “massive immediate climate benefits at a lower price than most other climate interventions.” In their view, this approach “should become one of aviation’s primary focuses in the coming years.”