A decade and change ago, as the world woke up to the catastrophe of climate change, campus activists were looking for ways to heal the environment at scale. They landed on an unusual one: the free market. Climate change is the world’s biggest unpriced externality, in that neither the producers nor the consumers of fossil fuels pay for the damage they cause to the environment. Gas is too cheap; ultimately, every living thing on the planet bears the cost. Perhaps activists could get the market to price that externality in by nudging investors to divest.

Students at dozens of universities, galvanized by the nonprofit 350.org, began protesting at academic-leadership and investment offices, asking for endowments to quit holding shares in fossil-fuel companies. The students picketed. They marched. They conducted sit-ins. They held votes. “You do not want your institution to be on the wrong side of this issue,” Stephen Mulkey, the president of Maine’s Unity College, the first to divest using 350.org’s guidelines, told Inside Climate News in 2012. “We realized that investing in fossil fuels was an unethical position.”

Still, the demands sounded symbolic at best, the movement brimming with idealism and energy but to what end? Companies like Chevron and ExxonMobil are profitable because of the world’s unslakable demand for gas; folks dumping their stocks would not change that. Such firms would “find other willing buyers” for the shares, Drew Faust, Harvard’s then-president, argued in response to students’ divestment campaign in 2013. And Harvard, she noted, used no small amount of light sweet crude itself.

But divestment had worked in other contexts: helping to end apartheid in South Africa, for instance. And the financial argument was, in theory, sound. Divestment can reduce a company’s value: Some folks sell their stock, others refuse to buy, the share price falls if there aren’t enough other, interested investors to step in. More important, it makes corporate growth more expensive. Exploration, mining, extraction, shipping—these are all extremely costly for energy firms. If such firms have less cash on hand and a harder time raising it, projects might not pencil out, energy prices might go up, and their profit margins might fall.

[Read: A major new index fund should unnerve climate-skeptical CEOs]

By 2018, less than a decade since the climate divestment movement picked up in the United States, more than 1,000 institutional investors with $6.2 trillion in assets under management had committed to divestment, the firm Arabella Advisors has estimated; some of today’s tallies are several times higher. The list of entities quitting fossil-fuel investment now includes several large pension funds, the country of Ireland, the Ford and Rockefeller foundations, and dozens of private colleges and universities. In 2021, Harvard (under new management) divested. In July, Seattle University did too. Last month, New York University, despite its deep ties with Wall Street, agreed to do so as well.  

Has it worked? On the margin perhaps. Some analyses find that the movement is still too small to have any effect. But one broad analysis of lending to oil-and-gas firms in 33 countries from 2000 to 2015 found that divestment was “associated with lower capital flows,” an effect “enhanced in more stringent environmental policy regimes and diminished in countries which heavily subsidize fossil fuels.”

But the single most important effect of divestment isn’t about the money at all, but something stranger and more diffuse: It takes away the “social license” of the fossil-fuel industry, as the movement’s leader, Bill McKibben, puts it. It makes extractive companies seem socially irresponsible and unworthy of public investment. It makes people think twice about working for such firms. It pushes all companies to acknowledge the environment, and to understand that being a major emitter is a bad business practice. It helps pressure corporate financiers to take climate seriously, something that really will keep the planet livable.

To be clear: A single person selling their Exxon stock is not going to change the trajectory of the climate crisis. A few families committing their 401(k) money to green funds is not going to hasten the world’s transition to renewable energy.

But McKibben is right. Symbolism matters. And if you are worried enough about the climate to want to take personal action, moving your money to green funds is one of the easiest ways to do it—one that takes perhaps five minutes, one time, plus a bit of emailing once a year. Contrast that with quitting meat, giving up your car, or stopping air travel.

If you like to pick your own stocks, the choice is simple: Either divest, or invest with intention. Just don’t buy stocks from major emitters, including coal, oil, and gas companies. Or buy the stocks of brown companies that really are trying to go green, rather than their less-green rivals. Tell these companies at shareholder meetings that you want them to commit to environmental standards. The economists Alex Edmans, of London Business School; Doron Levit, of the University of Washington; and Jan Schneemeier, of Indiana University, call this strategy “tilting.” “Divestment is most effective at starving a company of capital and hindering expansion, but tilting is more powerful” at getting a company to lower its emissions, the economists have found.   

[Read: Never acquire clothes the same way again]

Jacquelyn Pless, of MIT, has studied which kinds of corrective actions are meaningful in a corporate context—so you can know that the firms you’re investing in really are committed to saving the planet, or at least to not destroying it. She has found that companies that set long-term emissions targets, have a neutral party oversee their emissions data, tie executive compensation to environmental performance, support government climate-change bills, and set an internal carbon price do best in terms of lowered emissions.

If you like to invest in actively or passively managed funds rather than picking your own stocks, things get even easier. All of the major asset managers offer green mutual funds and index funds, meaning funds that do not put money into extractive industries and that hold companies in their portfolio to certain environmental standards. You can put or switch your money into them with nothing more than a few clicks. And let your fund manager or investment adviser know that you demand green funds: These companies manage gigantic pools of money and large shareholder voting blocs that are powerful influences on the companies whose stocks they hold.

There isn’t much downside to doing this. Green funds tend to do about as well as their conventional counterparts, at least for now. Perhaps the bigger issue is that there’s some evidence that companies in ESG funds do not actually have better environmental practices: There’s a lot of greenwashing going on. The answer for the individual is to do some due diligence, perhaps interviewing your fund manager and making sure that you are comfortable with where your money is going.

But don’t worry about it too much. The symbolism of green investment is more important than the dollars-and-cents effect. As many people as possible need to act like we are in a world worth saving. Becoming part of the divestment movement and greening your 401(k) is a quick and underappreciated way to do that.

You know the smell of warm, buttered popcorn. A crisp autumn day. The pungent, somewhat sweet scent that precedes rain. But could you begin to describe these aromas in detail? Or compare them? Your nose has some 400 olfactory receptors that do the work of translating the world’s estimated 40 billion odorous molecules into an even higher number of distinct scents your brain can understand. Yet although children are taught that grass is green and pigmented by chlorophyll, they rarely learn to describe the smell of a freshly cut lawn, let alone the ozone before a storm. The ability to express our sense of smell, in part because we’ve ignored it, eludes most of us.

Humans are not alone in this limitation. We have invented machines that can “see” and “hear”: Audio was first recorded and played back in 1877, and the first moving image followed a year later. A musical note is defined by its pitch, a single number, and computers represent a color with three numbers—the red, green, and blue (RGB) values that correspond to the types of color-receiving cells in our eyes. A song is a sequence of sounds, and an image, a map of pixels. But there has never been a machine that can flawlessly detect, store, and reproduce odors.

[Read: The hidden world of scents outside your door]

Scientists are working to change that. At the end of August, researchers published a paper presenting a model that can describe a molecule’s scent as well as, or even better than, a person (at least in limited trials). The computer program does so by placing molecules on a sort of odor map, where flowery smells are closer together than to, say, rotten ones. By quantitatively organizing odors, the research could mark a significant advance in enhancing our understanding of human perception. As it has already done for the study of vision and language, AI may be auguring a revolution in the study of this more enigmatic human sense.

“The last time we digitized a human sense was a generation ago,” Alex Wiltschko, a neuroscientist and a co-author of the paper, told me. “These opportunities don’t come around that often.” Computers can’t quite smell yet, but this research is a big step toward that goal, which Wiltschko began pursuing at Google Research and is now the focus of his start-up, Osmo. “People have been trying to predict smell from chemical structure for a long time,” Hiroaki Matsunami, a molecular biologist at Duke who studies olfaction and was not involved with the study, told me. “This is the best at this point in order to do that task. In that sense, it’s a great advance.”

Machine-learning algorithms require a huge amount of data to function, and the only information available for a scent comes from notoriously unreliable human noses and brains. (Even slight tweaks to a molecule can make a sweet, banana-scented compound reek of vomit; mysterious changes to your nose and brain, as many unfortunately learned from developing COVID-19, can make coffee smell of sewage.) Wiltschko and his team set out to identify and curate a set of roughly 5,000 molecules and associated odor descriptions (“alcoholic,” “fishy,” “smoky,” and so on) from researchers in the flavor and fragrance industries, then fed that data to a type of algorithm called a graph neural network, which was able to represent each molecule’s atoms and chemical bonds in a sort of internal diagram. The resulting program can, given a molecule’s structure, predict how it will smell as a combination of the existing odor labels.

Testing those predictions’ accuracy presented a whole other challenge. The team had to train a new, independent group of people to smell and label a new set of molecules that the program had never analyzed. “People are really bad at [describing scents] when they walk off the street,” Joel Mainland, a neuroscientist at the Monell Chemical Senses Center, in Philadelphia, who helped conduct the training for the study, told me. “If you train them for a couple hours, they get pretty good, pretty fast.”

Over five one-hour sessions, participants were given different substances associated with one of 55 different odors, such as kombucha (“fermented”), a crayon (“waxy”), or a green-apple Jolly Rancher (“apple”), to learn a reference point for each label. Participants then took a test in which they had to describe the smell of 20 common molecules (vanillin is vanilla-scented; carvone is minty), and then retook the test to make sure their judgments were consistent, Emily Mayhew, a food scientist at Michigan State University and co-author of the study, told me. Everybody who passed could help validate the algorithm.

The researchers curated a set of molecules that was highly distinct from the set used to train the program, then had participants smell and describe all of the new molecules with various labels, each rated from zero to five (hypothetically, a lemon might receive a five for “citrus,” a two for “fruity,” and a zero for “smoky.”). The average of all those ratings became the benchmark against which to compare the computer. “If you take two people and you ask them to describe a smell, they will often disagree,” Mainland said. But an average of several smell-trained people is “pretty stable.”

Overall, the AI model “smelled” a bit more accurately than the people participating in the research. The program provides “a really powerful demonstration that some key aspects of our odor perception are shared,” Sandeep Robert Datta, a neurobiologist at Harvard who did not conduct the research but is an informal adviser to Osmo, told me. Exactly what two people think a lemon smells like varies, but most will agree a lemon and an orange both smell of citrus, and an apple does not.

[Read: The difference between speaking and thinking]

Then there’s the study’s map. Every molecule, and in turn its odor, can be numerically represented in a mathematical space that the authors call a “principal odor map.” It provides insight into not just the relation between structure and smell but also the way our brain organizes odors, Wiltschko told me: Floral scents are in one section of the map, meaty ones in another; lavender is closer to jasmine on the map than it is to a beefy aroma.

Datta cautioned that he would not describe the odor map as principal so much as perceptual. “It does a beautiful job of capturing the relationship between chemistry and perception,” he said. But it doesn’t take into account all the steps—from receptors in our nose to the cerebral cortex in our brain—that occur as a molecule is turned into chemical signals that are then transformed into verbal descriptions of a smell. And the map isn’t like RGB values in that it doesn’t describe basic components that can make any smell—although it does “suggest to us that RGB [for smell] is possible.” The computer model’s perceptual odor map is an “extraordinarily important proof of concept,” he added, and provides crucial insights into how the brain appears to organize smells. For instance, you might assume certain categories of smell—citrus and smoky, for instance—are entirely separate, Datta said. But the odor map suggests that paths connect even these disparate scents.

The model is just the first in many advances needed to digitize scent. “It still lacks some of the important aspects of smell,” Matsunami told me, which the paper’s authors readily admit. Their program cannot predict how molecules smell in combination, and most natural odors are the results of very complex mixtures. It also wasn’t designed to take into account odor concentration, which can change not just the degree but also the quality of a smell (the molecule MMB, for instance, gives off a pleasant odor in small doses and is added to household cleaners, but in high concentrations it helps make cat urine smell like cat urine.) That the model also predicts a smell only on average makes it unclear how well the program would do in real-world settings, given people’s individual perceptions, Datta said. Even though the research is like the “Manhattan Project for categorizing odor qualities relative to physical, chemical parameters,” Richard Doty, the director of the Smell and Taste Center at the University of Pennsylvania, who was not involved with the study, told me, it’s unclear to him how much further the model can bring our understanding of smell given how complex our nose is. “I don’t know where it leads us.”

Still, future research could tackle some of these problems, Wiltschko argues, and fine-tune the map itself. The number of dimensions in the map, for instance, is arbitrarily set to optimize the computer program; changes in the training data might improve the model as well. And studying other parts of our olfactory system, such as receptors in our nose or neural pathways to the brain, will likely also help reveal more about how and through what stages the human body processes various smells. One day, a set of programs that can translate the structure, concentration, and mixture of molecules into a smell, paired with a chemical sensor, could truly realize digital olfaction.

Even without proper Smell-o-Vision, it is shocking, in a sense, that a computer model removed from the facts of human embodiment—a program has no nose, olfactory bulb, or brain—can reliably predict how something smells. “The paper implicitly advances the argument that you don’t need to understand the brain in order to understand smell perception,” Datta said. The research reflects a new, AI-inflected scientific understanding that seems to be popping up everywhere—using chatbots to study the human brain’s language network, or using deep-learning algorithms to fold proteins. It is an understanding rooted not in observation of the world so much as that of data: prediction without intuition.

The terror attack on Israel by Hamas has been a divisive—if clarifying—moment for the left. The test that it presented was simple: Can you condemn the slaughter of civilians, in massacres that now appear to have been calculatedly sadistic and outrageous, without equivocation or whataboutism? Can you lay down, for a moment, your legitimate criticisms of Benjamin Netanyahu’s government, West Bank settlements, and the conditions in Gaza, and express horror at the mass murder of civilians?

In corners of academia and social-justice activism where the identity of the oppressor and the oppressed are never in doubt, many people failed that test. In response to a fellow progressive who argued that targeting civilians is always wrong, the Yale professor Zareena Grewal replied: “Settlers are not civilians. This is not hard.” (She has since locked her X account.) Chicago’s Black Lives Matter chapter posted a picture of a paraglider, referencing the gunmen who descended on civilians at a music festival near the Gaza border from the air. (The chapter said in a statement that “we aren’t proud” of the post, which was later deleted.) Harvard student groups posted a letter stating that its signatories “hold the Israeli regime entirely responsible for all unfolding violence.” (Several of the named groups have since withdrawn their endorsement.)

The New York branch of the Democratic Socialists of America promoted a rally where protesters chanted “resistance is justified when people are occupied” and one participant displayed a swastika. These actions prompted criticism by Representative Alexandria Ocasio-Cortez, perhaps the DSA’s most prominent figure, and the resignation of members including the comedian Sarah Silverman. In a statement, the New York City Democratic Socialists regretted the “confusion” that its rhetoric had caused, but added: “We are also concerned that some have chosen to focus on a rally while ignoring the root causes of violence in the region, the far-right Netanyahu government’s escalating human rights violations and explicitly genocidal rhetoric, and the dehumanization of the Palestinian people.”

[Gal Beckerman: The left abandoned me]

In the United Kingdom, where I live, a journalist for the hard-left outlet Novara, Rivkah Brown, tweeted that “the struggle for freedom is rarely bloodless and we shouldn’t apologise for it.” (She has since deleted the post, saying she responded “too quickly and in a moment of heightened emotion.”) Ellie Gomersall, the president of the National Union of Students in Scotland, apologized for reposting content justifying Hamas’s actions. Two days earlier, Gomersall had accused the British Labour Party leader Keir Starmer of being “complicit in the deaths of … trans people” for saying that “a woman is a female adult.” Got that? A politician with an essentialist view of womanhood is complicit in the deaths of innocents, but a terrorist indiscriminately murdering people at a music festival must be understood in context.

In the fevered world of social media, progressive activists have often sought to discredit hateful statements and unjust policies by describing them as “violence,” even “genocide.” This tendency seems grotesque if the same activists are not prepared to criticize Hamas, a group whose founding charter is explicitly genocidal: “The Day of Judgement will not come about until Moslems fight the Jews (killing the Jews), when the Jew will hide behind stones and trees.”

Many of those making inflammatory statements come from what’s sometimes known as the “intersectional left.” This tendency is strongly influenced by the academic disciplines of queer theory and critical race theory, and by the postcolonial idea of the “subaltern,” or marginalized class. Like woke, intersectionality has become a boo-word for the right—but unlike woke, it is a label that some activists proudly embrace, particularly academics and young feminists.

I will go to my grave defending the original conception of intersectionality, a legal doctrine advanced by the American critical race theorist Kimberlé Crenshaw. She made the useful observation that civil-rights legislation has usually treated protected characteristics such as sex and race as discrete, when in fact they are often interlinked. One of her examples was a St. Louis car plant that, for many years, hired white women and Black men but never Black women. Even after management stopped discriminating, Black women always ranked low on the seniority list and therefore were especially vulnerable to layoffs. Yet how could they sue when they were not subject to racism or sexism per se, but an intersection of the two?

However, Crenshaw herself has expressed surprise at how the meaning of intersectionality has changed through its invocation in pop culture. “This is what happens when an idea travels beyond the context and the content,” she told Vox in 2019. In escaping from the academy into the mainstream, intersectionality morphed into both a crude tallying of oppression points and an assumption that social-justice struggles fit neatly together—with all of the marginalized people on one side and the powerful on the other.

That’s how you end up with Queers for Palestine when being queer in Palestine is difficult and dangerous. (In 2016, a Hamas commander was executed after being accused of theft and gay sex.) It’s also how you end up with candidates for Labour Party leadership signing a pledge that insists there “is no material conflict between trans rights and women’s rights,” even when—as in the eligibility rules for women’s sports—some wins for one group plainly come at the expense of the other. The pop version of intersectionality cannot deal with the complexity of real human life, where we can all be, in Jean-Paul Sartre’s phrase, “half-victims, half-accomplices, like everyone else.” In fact, you can support the Palestinian cause without excusing acts of terrorism committed by Hamas. You can question Israel’s military response without excusing acts of terrorism committed by Hamas.

Eliot A. Cohen: Against barbarism

Fitting Israel into the intersectional framework has always been difficult, because its Jewish citizens are both historically oppressed—the survivors of an attempt to wipe them out entirely—and currently in a dominant position over the Palestinians, as demonstrated by the Netanyahu government’s decision to restrict power and water supplies to Gaza. The simplistic logic of pop intersectionality cannot reconcile this, and the subject caused schisms within the left long before Saturday’s attacks. In 2017, Linda Sarsour, one of the organizers of the Women’s March, told The Nation that Zionism and feminism were incompatible: “It just doesn’t make any sense for someone to say, ‘Is there room for people who support the state of Israel and do not criticize it in the movement?’ There can’t be in feminism.” In January 2018, several pro-Palestinian groups boycotted a Women’s March because it featured the actor Scarlett Johansson, who once made an ad for an Israeli company that has a factory in the West Bank. On the other side, Jewish groups condemned three of the Women’s March organizers, including Sarsour, for associating with the openly anti-Semitic Nation of Islam leader Louis Farrakhan.

The leftist belief in the righteousness of “punching up,” a derivation of standpoint theory, is also important here. Again, this idea has mutated from the reasonable observation that different groups have different knowledge based on their experience—I have never experienced being pulled over by a traffic cop as a Black man, and that limits my understanding of the police—to the idea that different rules apply to you depending on your social position. When an oppressed group uses violence against the oppressor, that is justified “resistance.” Many of us accept a mild version of this proposition: The British suffragettes turned to window smashing and bombing after deciding that letter writing and marches were useless, and history now remembers them as heroines. But somehow, in the case of the incursion from Gaza into Israel, the idea of “punching up” was extended to the murder of children. I simply cannot comprehend how any self-proclaimed feminist can watch footage of armed militants manhandling a woman whose pants are soaked with what looks like blood and decide that she has the power in that situation—and deserves her fate.

The sheer number of apologies and climb downs that followed the initial wave of inflammatory posts suggests that some of their authors issued knee-jerk statements of solidarity before they understood exactly what they were endorsing. As the full extent of the weekend’s barbarity becomes clear, some on the intersectional left are—to their small credit—revising their initial reactions. But others are doubling down. Confronted with real violence by genocidal terrorists, they failed the test.