America is failing women’s health

OPINION: Systemic inequity means women in the US die younger and suffer more than they should. It’s time for health for all.

By Susan E. Short By Meghan Zacher

One of the big news stories of 2022 was the overturn of Roe v. Wade, which threw America’s appalling treatment of women’s reproductive health into the international spotlight. But the problem of how the US is failing women’s health goes far beyond abortion rights. This wider issue deserves more attention.

The state of women’s health in the US is shocking — even to us, medical sociologists and demographers with a history of studying gender and health. Population health statistics paint a sobering portrait. Women in the US fare poorly in one way or another compared with women in other high-income countries, compared with US men, and even compared with previous generations of American women. And there’s no sign that these patterns are improving.

Mortality statistics show that US women live substantially shorter lives than women in other high-income countries. While US women’s life expectancy at birth was similar to the average across 23 comparison nations in the Organization for Economic Cooperation and Development in 1980, by 2019 the US had fallen to the bottom of the pack. That year, US women’s life expectancy was 81.4 years — 3.2 years lower than the average across those comparison nations and more than four years lower than in Italy, Switzerland, France, Spain and Japan.

US rates of maternal mortality and  severe maternal morbidity — “near-miss” events that could have resulted in death — are inexcusable. They have been rising for decades, with troubling increases in recent years. Between 2018 and 2020, the  US maternal mortality rate increased from 17.4 deaths per 100,000 live births to 23.8. For comparison, in 2020, the US maternal mortality rate was  more than three times higher than that of 10 other high-income countries, including Canada, the UK and Germany. A  2022 CDC report suggests most pregnancy-related deaths in the US are preventable.

Delivery isn’t the only risk to pregnant people in the US: They die even more often from homicide than they do from pregnancy-related causes. Homicide also ranks among the  top five causes of death for girls and women up to age 44 in the US overall.

Women’s health in the US and elsewhere also suffers needlessly from the silence and stigma about female bodies that persist in science, medicine and society. The lack of science on the clitoris,  even its basic anatomy, is a notable example.  Experts agree, too, that our understanding of basic uterine and menstrual physiology is lacking. Endometriosis, a painful and poorly understood condition that involves endometrial tissue growing outside the uterus,  affects over 11 percent of women aged 15 to 44 in the US, many of whom wait years for a diagnosis. Millions more suffer during menopause from night sweats, memory lapses and sleep difficulties. Too many dismiss all this pain and suffering as natural — something to be endured.

The leading cause of death among US women is heart disease. A  2022 study of emergency room visits by adults 55 and under revealed that women who came in with chest pain waited longer to see a doctor or nurse and were less likely to be admitted for observation than men. A 2009 experimental study found that when women and men reported exactly the same cardiovascular symptoms,  doctors were less certain of how to diagnose women than men, and were twice as likely to misdiagnose middle-aged women with a mental health condition compared with men.

Similar things happen with other health conditions. For example, women who came to an emergency room with abdominal pain in the US  waited longer for pain medication, and were less likely to be given opioid analgesics, than men.

These statistics all point in the same direction. The United States is failing women’s health. But why?

People often assume that the main reason for women’s poor health is underlying sex-based biology. But biology is unlikely to explain why women in the US die younger than women in other high-income countries. Neither is health care spending. The US spends more per capita on health care than any other country in the world.

The root cause of US women’s poor health is non-medical. It is systemic inequity: everything from unfair structures and practices that benefit the advantaged, to gender bias in science, to cultural expectations about what can and should be. Scientists have shown how sexism — together with racism, nativism, ablism, and other systems of privilege and oppression — shape the scientific questions we ask, as well as our everyday experiences, with profound implications for health.

It’s powerfully telling that Indigenous women and Black women in the US are two to three times more likely to die from pregnancy-related complications than white women. That less educated women die years earlier than more educated women, and that women in Mississippi die younger than women in Massachusetts. Some suggest that the source of these inequalities lies in preexisting chronic conditions and things like obesity, smoking and individual actions labeled “health behaviors” that are assumed to be a matter of personal choice. But this misses the point. These differences, too, reflect systemic inequity. Our bodies — indeed, our biology — do not exist apart from our social surroundings.

To make change, a shift towards equity — in and out of science — is needed.

Inclusive science means, among other things, equitable funding. Despite progress, a 2021 study reported that the National Institutes of Health (NIH) — the largest public funder of health research in the US — tends to overfund research on diseases that disproportionately affect men, while underfunding those primarily affecting women. Funding for research on the health of transgender and gender non-binary people also lags. On the hopeful side, the NIH’s Office of Research on Women’s Health, the National Institute on Minority Health and Health Disparities, and the Office of Behavioral and Social Science Research, among others, are working to advance research on the social foundations of health. That should be applauded.

The overturn of Roe v. Wade, and recent moves to legislate abortion bans, undermine everyone’s health. Laws matter, and changing laws in the direction of equity (instead of away from it), would be an important step. But laws alone can’t create the shift we need. Systemic injustice courses through all sectors, and will give rise to unjust legislation or practices again and again. We need a wholescale social movement that is broader.

We need to think things can and should be different, and make them so. Systems and structures rely on people to create and maintain them. The progress of the MeToo and Black Lives Matter movements are signs of hope. We can get there: It’s time to double down and advocate for health for all.

Lea en español

10.1146/knowable-121922-1

Susan E. Short and Meghan Zacher are sociologists at the Population Studies and Training Center at Brown University. They research the social foundations of health.

Susan E. Short and Meghan Zacher are sociologists at the Population Studies and Training Center at Brown University. They research the social foundations of health.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

The obscure calculation transforming climate policy

After long debate, economists and philosophers are reaching consensus on how to value future generations

By Ula Chrobak

Barring a mass Homo sapiens extinction event from, say, nuclear war or another disaster, many more billions of humans will be born on the Earth in the coming millennia. For philosophers and economists, this poses a tricky question: What do we owe these future humans? How should we divide our resources between the 8 billion people alive now and those to come?

This isn’t just fodder for a thorny thought experiment. While it’s not often stated explicitly, all governments make trade-offs with the welfare of future generations when they make decisions that have long-term consequences, such as those related to energy production and infrastructure. Economists have even devised calculations to better explore such trade-offs, as well as a key variable — the social discount rate — which has been the subject of a hot debate for at least the past 15 years.

Just last month, the Biden Administration proposed a consequential change for how the United States handles the math used to probe this ethical question. Officials recommended that the government nearly quadruple its social cost of carbon — a monetary estimate of the costs to the economy, environment and human welfare for every ton of carbon dioxide emitted into the atmosphere.

This value can be used to calculate, in dollars, the effect of various actions, such as the benefit of avoided carbon emissions from a new subway route or the costs of building natural gas lines. To reach this new estimate, officials used a new social discount rate: 2 percent, down from the 3 percent used previously (a larger discount rate translates into a lower cost). Because the resulting social cost of carbon is so much higher, this change makes it suddenly look far more costly to pollute — or to approve policies that would increase greenhouse gas emissions.

Climate policy wonks, many of whom wrote to the government to voice their opinions, closely watched this development because it could lead to a shift in how the US — the world’s greatest cumulative emitter of greenhouse gases — regulates its contribution of climate-heating gases. But the US is just one of many entities using social discount rates to estimate how much it’s worth, in today’s dollars, to avoid billions in climate damage in future decades.

Across influential institutions around the world — including governments as well as financial organizations such as the World Bank — economists punch social discount rates into mathematical formulas to weigh the future costs and benefits of proposals to build new bridges and roads, invest in clean energy research and regulate greenhouse gases. You’re probably already familiar with the results of these analyses, even if you didn’t know about social discount rates. Consider when a politician says that a proposed environmental regulation would cause too much harm to the economy, for example. How do officials make those calls? The secret ingredient is social discount rates. 

“It is probably the single most important variable in terms of working out what you have to do for climate change mitigation,” says Mark Freeman, an economist focused on intergenerational finance at the University of York and coauthor of a recent review of social discounting in the Annual Review of Resource Economics. He concludes this based on current research that found that the social cost of carbon is more sensitive to policymakers’ choice of discount rate than other variables. “People need to worry about this more. It matters.” 

Seemingly small changes in discount rates can result in vastly different climate policy outcomes. During the Trump administration, officials claimed that a rollback in automobile fuel efficiency standards would result in $6.4 billion in economic benefits. They based their calculations on a discount rate of 7 percent, which “basically means you don’t care about anything that happens after about 25 years,” says Ben Groom, an economist at the University of Exeter and lead author of the Annual Review of Resource Economics paper. Under President Barack Obama, those same fuel efficiency standards had been deemed to produce a net economic benefit based on a 3 percent discount rate.

Economists use discounting to weigh the pros and cons of getting things sooner rather than later. For individuals, such calculations can be pretty straightforward: “If I were to offer you a Lamborghini today or a Lamborghini in 10 years, who’s going to wait for 10 years?” Freeman sometimes asks his students. Our preference for getting that Lambo today — or an equivalent sum of cash, if you don’t care for sports cars — isn’t just impatience. It’s rational, in economic terms. A hundred dollars is, generally, going to be worth more if you get it today rather than in a year. That’s due to factors like inflation, as well as the lost opportunity to invest your Benjamin today and watch it grow with compound interest.

When economists consider the impacts of an investment today on the welfare of large groups of people, the discount rate becomes a social discount rate — and weighing the factors that influence the rate gets more complicated. One reason is that policymakers can’t snap their fingers and pour money into every public need at once. Instead, they have to assess the most cost-effective use of funds by adding up all the costs of a program or policy, then adding up all the benefits, and comparing the two price tags.

These comparisons are relatively easy when considering a project with immediate results, such as an investment in schools or safe drinking water. But sometimes officials have to compare near-term priorities with projects that may not fully pay off for 100 or more years, as is the case with many climate policies. It’s not always selfishness that might prevent policymakers from acting on climate change, says Tamma Carleton, an economist at the University of California, Santa Barbara. “They are also trying to think about our educational systems, poverty eradication and healthcare.”

Economists use social discount rates to determine how much a future benefit, like $1 trillion in averted climate damages in 2100, would be worth today, explains Carleton. In the US, federal agencies are required to prepare cost-benefit analyses for projects that could have a large economic impact now or in the future. If the benefits far outweigh the costs, a proposed rule or bill is more likely to be seen as viable and move forward.

But here you might say, is it really necessary to discount future people in order to do these comparisons?

Welcome to one of the most consequential yet obscure ethical debates known to humankind. About 15 years ago, Nicholas Stern, a climate economist at the London School of Economics, set off an argument about discounting that continues today. In the 2006 UK government study led by Stern, The Economics of Change: The Stern Review, he used a social discounting approach that explicitly took our ethical responsibility to future generations into account.

Stern used a very low discount rate, 1.4 percent, to support the conclusion that large investments were urgently needed to prevent future climate damages. That value — while still discounting a small amount for future economic growth and the possibility of human extinction — treated the welfare of future generations equally. As he and coauthors summed up, “if a future generation will be present, we suppose that it has the same claim on our ethical attention as the current one.”

However, future economic growth is not 100 percent guaranteed, and the damage wrought by climate change could worsen life for individuals in the next century. In this scenario, some economists have argued, using a zero or even a negative discount rate would make the most sense.

These arguments have irked some economists, including William Nordhaus of Yale University, who was awarded a Nobel Prize in 2018 for his work in climate change economics. “The Review takes the lofty vantage point of the world social planner, perhaps stoking the dying embers of the British Empire, in determining the way the world should combat the dangers of global warming,” he wrote in a paper published in the Journal of Economic Literature. Nordhaus thought that Stern’s approach risked impoverishing people today to tackle future climate change, and favored a higher discount rate based on market interest and savings rates.

Today, most economists favor some amount of discounting, for two reasons: People tend to be impatient, and future people will be richer than today’s. This desire for more immediate payoff isn’t necessarily a bad thing, says Freeman. Most of us already discount future people, he points out. “I mean, I love my children more than I love my great-, great-, great-grandchildren,” he says. “So why should I not value my children more than my great-, great-, great-grandchildren?”

While it may seem intuitive to say future people deserve the same consideration as people today, many economists counter that the people of the future will probably be richer as a result of economic growth. And the same sum of money is less meaningful for a rich person compared to a poor person. “One hundred dollars matters more for me than it does for Jeff Bezos,” says Carleton. Adds Groom: “If the future is richer, then we are the poor people.” Groom and others argue that putting money toward future people without discounting is like taking money from the poor to give to the rich.

Some experts — including economists and philosophers focused on intergenerational ethics — add that we need to consider the possibility that the human species will go extinct. It would be a shame, they say, to go all in on programs benefiting humans hundreds of years from now, only for them to end up dying out due to a meteorite or nuclear war.

Increasingly, governments are using lower discount rates to reflect the urgent need to address climate-warming emissions. The recent US Environmental Protection Agency report used a 2 percent discount rate as one factor in recalculating the social cost of a ton of carbon, down from the 3 percent rate used by the Obama administration. The adjustment contributed to an increase to $190 from $51 per ton. Earlier, at the end of 2020, New York State officials updated their own social cost of carbon to $125 a ton, also by using a discount rate of 2 percent. The change affects many government decisions, explains Maureen Leddy, director of the state’s office of climate change. For example, an agency purchasing new vehicles for its fleet has to factor in the social cost of carbon emissions generated by buying gas-powered cars, which could make electric vehicles look much less expensive in comparison. 

But why is 2 percent so hot these days? One reason is that the rate seems to bridge the ethics-versus-pure-economics divide. In survey research, Freeman and Groom found that the median discount rate chosen by both economists and philosophers was 2 percent, which in turn supports policy actions that are expected to limit global warming to 1.5°C by 2100. The two groups don’t necessarily get to that number the same way, but they seem to agree that rate is best for discounting long-term government projects, such as those that would affect climate change. 

That said, it might not be fair to use the same low social discount rates worldwide. A low discount rate might motivate climate action in richer countries, but shouldn’t necessarily be used in less developed countries, explains Nfamara Dampha, a researcher of natural capital and ecosystem services at the University of Minnesota and an author of a review on discounting and environmental change in the Annual Review of Environment and Resources. “The problem with [using] the same approach in developing countries is that there is already a lot of poverty, there is already a lot of inequality,” he says. By using a low discount rate, “you’re constraining those people to minimize their consumption for the benefit of the future.” 

For countries with acute problems such as a lack of clean water, higher discount rates may be warranted to direct public funds toward the immediate benefits of alleviating such issues. Meanwhile, Dampha says that wealthier countries that have contributed a large share of climate-warming emissions should use low discount rates when funding environmental projects in developing countries, as a matter of climate justice. “The payments for ecosystem services should be sourced globally to developing countries,” he says. 

In the future, Freeman hopes that the public can be more involved in discussions involving social discount rates. “At the moment, it’s all very behind closed doors, which isn’t great,” he says. “Why should I have any special say in what the discount rate is?” At their core, after all, these social discount rates are political decisions — ones that can directly impact policies, including how to temper the worst effects of climate change.

10.1146/knowable-120622-1

Ula Chrobak is a freelance science journalist based in Reno, Nevada. You can read more of her work at her website: ulachrobak.com.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

Fiber optics take the pulse of the planet

It’s like radar, but with light. Distributed acoustic sensing — DAS — picks up tremors from volcanoes, quaking ice and deep-sea faults, as well as traffic rumbles and whale calls.

By Carolyn Wilke

Andreas Fichtner strips a cable of its protective sheath, exposing a glass core thinner than a hair — a fragile, 4-kilometer-long fiber that’s about to be fused to another. It’s a fiddly task better suited to a lab, but Fichtner and his colleague Sara Klaasen are doing it atop a windy, frigid ice sheet.

After a day’s labor, they have spliced together three segments, creating a 12.5-kilometer-long cable. It will stay buried in the snow and will snoop on the activity of Grímsvötn, a dangerous, glacier-covered, Icelandic volcano.

Sitting in a hut on the ice later on, Fichtner’s team watches as seismic murmurs from the volcano beneath them flash across a computer screen: earthquakes too small to be felt but readily picked up by the optical fiber. “We could see them right under underneath our feet,” he says. “You’re sitting there and feeling the heartbeat of the volcano.”

Fichtner, a geophysicist at the Swiss Federal Institute of Technology in Zurich, is one of a cadre of researchers using fiber optics to take the pulse of our planet. Much of this work is being done in remote places, from the tops of volcanoes to the bottoms of the seas, where traditional monitoring is too costly or difficult. There, in the last five years, fiber optics have started to shed light on seismic rumblings, ocean currents and even animal behaviors.

Grímsvötn’s ice sheet, for example, sits on a lake of water thawed by the volcano’s heat. Data from the new cable reveal that the floating ice field serves as a natural loudspeaker, amplifying tremors from below. The work suggests a new way to eavesdrop on the activity of volcanoes that are sheathed by ice — and so catch tremors that may herald eruptions. 

Like radar, but with light

The technique used by Fichtner’s team is called distributed acoustic sensing, or DAS. “It’s almost like radar in the fiber,” says physicist Giuseppe Marra of the United Kingdom’s National Physical Laboratory in Teddington, England. While radar uses reflected radio waves to locate objects, DAS uses reflected light to detect events, from seismic activity to moving traffic, and to determine where they occurred.

It works like this: A laser source at one end of the fiber shoots out short pulses of light. As a pulse moves along the fiber, most of its light continues forward. But a fraction of the light’s photons bang into intrinsic flaws in the fiber — spots of abnormal density. These photons scatter, some of them traveling all the way back to the source, where a detector analyzes this reflected light for hints about what occurred along the fiber’s length.

An optical fiber for DAS typically stretches several to tens of kilometers, and it moves or bends in response to disturbances in the environment. “It wiggles as cars go by, as earthquakes happen, as tectonic plates move,” says earth scientist Nate Lindsey, coauthor of a 2021 article on fiber optics for seismology in the  Annual Review of Earth and Planetary Sciences. Those wiggles change the reflected light signal and allow researchers to tease out information such as how an earthquake bent a cable at a certain point.

An optical cable captures vibrations, for instance, of seismic tremors along its whole length. In contrast, a typical seismic sensor, or seismometer, relays information from only one spot. And seismometers can be costly to deploy and difficult to maintain, says Lindsey, who works at a company called FiberSense that is using fiber-optic networks for applications in city settings.

DAS can provide about 1 meter resolution, turning a 10-kilometer fiber into something like 10,000 sensors, Lindsey says. Researchers can sometimes piggyback off existing or decommissioned telecommunications cables. In 2018, for example, a group including Lindsey, who was then at UC Berkeley and Lawrence Berkeley National Laboratory, turned a 20-kilometer cable operated by the Monterey Bay Aquarium Research Institute — normally used to film coral, worms and whales — into a DAS sensor while the system was offline for maintenance.

“The ability to just go under the seafloor for tens of kilometers — it is remarkable that you can do that,” Lindsey says. “Historically, deploying one sensor on the seafloor can cost $10 million.”

During their four-day measurement, the team caught a 3.4-magnitude earthquake shaking the ground some 30 kilometers away in Gilroy, California. For Lindsey’s team, it was a lucky strike. Earth scientists can use seismic signals from earthquakes to get a sense of the structure of the ground that the quake has traveled through, and the signals from the fiber-optic cable allowed the team to identify several previously unknown submarine faults. “We’re using that energy to basically illuminate this structure of the San Andreas Fault,” Lindsey says.

Eavesdropping on cities and cetaceans

DAS was pioneered by the oil and gas industry to monitor wells and detect gas in boreholes, but researchers have been finding a variety of other uses for the technique. In addition to earthquakes, it has been harnessed to monitor traffic and construction noise in cities. In densely populated metropolises with significant seismic hazards, such as Istanbul, DAS could help to map the sediments and rocks in the subsurface to reveal which areas would be the most dangerous during a large quake, Fichtner says. A recent study even  reported eavesdropping on whale songs using a seabed optical cable near Norway.

But DAS comes with some limitations. It’s tricky to get good data from fibers longer than 100 kilometers. The same flaws in the cables that make light scatter — producing the reflected light that is measured — can deplete the signal from the source. With enough distance traveled, the original pulse would be completely lost.

But a newer, related method may provide an answer — and perhaps allow researchers to spy on a mostly unmonitored seafloor, using existing cables that shuttle the data of billions of emails and streaming binges.

In 2016, Marra’s team sought a way to compare the timekeeping of ultraprecise atomic clocks at distant spots around Europe. Satellite communications are too slow for this job, so the researchers turned to buried optical cables instead. At first, it didn’t work: Environmental disturbances introduced too much noise into the messages that the team sent along the cables. But the scientists sensed an opportunity. “That noise that we want to get rid of actually contains very interesting information,” Marra says.

Using state-of-the-art methods for measuring the frequency of light waves bouncing along the fiber-optic cable, Marra and colleagues examined the noise and found that — like DAS — their technique detected events like earthquakes through changes in the light frequencies.

Instead of pulses, though, they use a continuous beam of laser light. And unlike in DAS, the laser light travels out and back on a loop; then the researchers compare the light that comes back with what they sent out. When there are no disturbances in the cable, those two signals are the same. But if heat or vibrations in the environment disturb the cable, the frequency of the light shifts.

With its research-grade light source and measurement of a large amount of the light initially emitted — as opposed to just what’s reflected — this approach works over longer distances than DAS does. In 2018, Marra’s team demonstrated that they could detect quakes with undersea and underground fiber-optic cables up to 535 kilometers long, far exceeding DAS’s limit of around 100 kilometers.

This offers a way to monitor the deep ocean and Earth systems that are usually hard to reach and rarely tracked using traditional sensors. A cable running close to the epicenter of an offshore earthquake could improve on land-based seismic measurements, providing perhaps minutes more time for people to prepare for a tsunami and make decisions, Marra says. And the ability to sense changes in seafloor pressure may open the door to directly detecting tsunamis too.

In late 2021, Marra’s team managed to sense seismicity across the Atlantic on a 5,860-kilometer optical cable running on the seafloor between Halifax in Canada and Southport in England. And they did so with far greater resolution than before, because while earlier measurements relied on accumulated signals from across the entire submarine cable’s length, this work parsed changes in light from roughly 90-kilometer spans between signal-amplifying repeaters.

Fluctuations in intensity of the signal picked up on the transatlantic cable appear to be tidal currents. “These are essentially the cable being strummed as a guitar string as the currents go up and down,” Marra says. While it’s easy to watch currents at the surface, seafloor observations can improve an understanding of ocean circulation and its role in global climate, he adds.

So far, Marra’s team is alone in using this method. They’re working on making it easier to deploy and on providing more accessible light sources.

Researchers are continuing to push sensing techniques based on optical fibers to new frontiers. Earlier this year, Fichtner and a colleague journeyed to Greenland, where the East Greenland Ice-Core Project is drilling a deep borehole into the ice sheet to remove an ice core. Fichtner’s team then lowered a fiber-optic cable 1,500 meters, by hand — and caught a cascade of icequakes, rumbles that result from the bedrock and ice sheet rubbing together.

Icequakes can deform ice sheets and contribute to their flow toward the sea. But researchers haven’t had a way before now to investigate how they happen: They are invisible at the surface. Perhaps fiber optics will finally bring their hidden processes into the light.

Lea en español

Carolyn Wilke is a Chicago-based freelance science journalist. Find her on Twitter @carolynmwilke.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

Are we ready? Understanding just how big solar flares can get

Recasting the iconic Carrington Event as just one of many superstorms in Earth’s past, scientists reveal the potential for even more massive, and potentially destructive, eruptions from the sun

By Christopher Crockett

On May 1, 2019, the star next door erupted.

In a matter of seconds, Proxima Centauri, the nearest star to our sun, got thousands of times brighter than usual — up to 14,000 times brighter in the ultraviolet range of the spectrum. The radiation burst was strong enough to split any water molecules that might exist on the temperate, Earth-sized planet orbiting that star; repeated blasts of that magnitude might have stripped the planet of any atmosphere.

It would be bad news if the Earth’s sun ever got so angry.

But the sun does have its moments — most famously, in the predawn hours of September 2, 1859. At that time, a brilliant aurora lit up the planet, appearing as far south as Havana. Folks in Missouri could read by its light, while miners sleeping outdoors in the Rocky Mountains woke up and, thinking it was dawn, started making breakfast. “The whole of the northern hemisphere was as light as though the sun had set an hour before,” the Times of London reported a few days later.

Meanwhile, telegraph networks went haywire. Sparks flew from equipment — some of which caught on fire — and operators in Boston and Portland, Maine, yanked telegraph cables from batteries but kept transmitting, powered by the electrical energy surging through the Earth.

The events of that Friday evoked biblical descriptions. “The hands of angels shifted the glorious scenery of the heavens,” reported the Cincinnati Daily Commercial. The actual impetus was a bit more prosaic: The skies had been set ablaze by an enormous blob of electrically charged gas, shot out from the sun following a flash of light known as a solar flare.

Such a blob — a tangle of plasma and magnetic fields — is known as a coronal mass ejection. Upon arrival at Earth, such an ejection can trigger the most ferocious of geomagnetic storms. The 1859 storm, named the Carrington Event for the scientist who witnessed the flare that preceded it, has long been upheld as the most powerful wallop that the sun has ever delivered.

But in recent years, research has indicated that the Carrington Event was just a taste of what the sun can throw at us. Tree rings and ice cores encode echoes of dramatically stronger solar storms in the distant past. And other stars, such as Proxima Centauri, show that even the most energetic documented solar outbursts pale in comparison with what is possible.

Nevertheless, the Carrington Event offers important clues to what the sun might have in store for Earth in the future, solar physicist Hugh Hudson writes in the 2021 Annual Review of Astronomy and Astrophysics. “Danger lurks for humanity’s technological assets, especially those in space,” writes Hudson, of the University of Glasgow. In the wake of a Carrington-like event today, entire power grids could shut down and GPS satellites could be knocked offline.

Understanding just how severe solar storms can be provides insights into what the universe may sling our way — and maybe how to foretell the next one so that we’re better prepared when it happens.

Anatomy of a flare

Roughly 18 hours before the 1859 event brightened Earth’s skies, an English astronomer noticed something strange on the surface of the sun.

While working in his observatory, Richard Carrington saw two brilliant points of light emerge from among a clutch of dark sunspots and vanish within five minutes. Another English astronomer, Richard Hodgson, saw the same thing, noting that it was as if the brilliant star Vega had appeared on the sun. At the same time, compass-like needles at England’s Kew Observatory twitched, a hint of the magnetic storm about to ensue.

Before then, no one knew about solar flares — mostly because no one was tracking sunspots every clear day the way Carrington was. Decades would pass before astronomers and physicists could unravel the physics of solar flares and their impact on Earth.

A solar flare is an eruption on the sun, a sudden flash of light — usually near a sunspot — that can release as much energy as roughly 10 billion 1-megaton nuclear bombs. The trigger is a sudden, localized release of pent-up magnetic energy that blasts out radiation across the entire electromagnetic spectrum, from radio waves to gamma rays.

Many solar flares, though not all, are accompanied by a coronal mass ejection, a massive chunk of the sun’s hot gas blown into space along with a tangle of magnetic fields. Billions of tons of sun stuff can billow out into the solar system, crossing the 150 million kilometers to Earth’s orbit in anywhere from about 14 hours to a few days. 

Most solar eruptions miss our planet by a wide margin. But occasionally, one gets aimed right at Earth. And that’s when things can get interesting.

About eight minutes after a solar flare, its light reaches Earth in a flash of visible light. That’s also when a spike in ultraviolet light and X-rays sprays the upper atmosphere, causing a slight magnetic disturbance at the surface. That was the twitch the magnetic instruments at the Kew sensed in 1859.

The coronal mass ejection can trigger a geomagnetic storm when it encounters the magnetic field that envelops Earth. The disturbance to the magnetic field induces electrical currents to course through conductors, including wires and even the planet itself. At the same time, high-speed charged particles spewed by the sun crash into atoms in the upper atmosphere, lighting up the aurora.

The 1859 flare has long been, and remains, a standout in its energy and effects on Earth. Comparably powerful solar eruptions are often referred to as “Carrington events.” But it does not stand alone.

“It’s oftentimes described as the most intense storm ever recorded,” says Jeffrey Love, a geophysicist at the US Geological Survey in Denver. “That’s possibly not exactly true, but it certainly is one of the two most intense storms.” Or three or four.

In May 1921, the sun dealt our planet a geomagnetic storm on par with the Carrington Event. As in 1859, a brilliant aurora appeared well beyond the polar regions. Telegraph and telephone systems broke down, with some sparking destructive fires.

And just 13 years after Carrington spied his eponymous flare, another solar storm came along that by some measures may have topped it. “It looks now, based on aurora and sparse magnetometer measurements, that an event in 1872 was probably larger than the Carrington Event,” says Ed Cliver, a solar physicist retired from the US Air Force.

These storms show that the Carrington Event wasn’t a “black swan,” Hudson says. If anything, the sun has been holding back in the modern era. Evidence from the more distant past points to a few solar storms that make the Carrington Event seem almost puny by comparison.

Forgotten flares

Trees have long memories. Each year of growth chronicles tidbits about environmental conditions at the time in concentric annual rings. From those rings researchers can reconstruct scenes from Earth’s past.

Some cedar trees in Japan recall a tsunami of atomic particles hurled from the sun around the year 775. Those trees recorded a significant uptick in carbon-14, a radioactive variant of carbon that trees absorb from the atmosphere. Carbon-14 emerges from run-ins between atmospheric nitrogen and cosmic rays — high-speed particles from space that pummel our planet daily. Some solar flares shower Earth with an excess of cosmic rays, which ramps up production of carbon-14. The change in carbon-14 levels recorded in 775 was about 20 times larger than the normal ebb and flow from the sun, researchers reported in 2012.

“The clear suggestion there was that super events could happen, because this was a factor of 10 — if it was a solar flare — a factor of 10 or 20 or more greater than the Carrington Event,” Hudson says.

A carbon-14 boost in tree rings showed signs of another sizable solar event in 994. Ice cores from Antarctica showed a corresponding increase, in both 994 and 775, of beryllium-10, another product of cosmic rays — adding more certainty to the tree ring findings.

Looking farther back in time, a study of ice cores suggests a third similar event around 660 BCE. And in August (in a paper still undergoing peer review), researchers reported two more  carbon-14 spikes in tree rings from around 7176 BCE and 5259 BCE, possibly on par with the 775 event.

It’s hard to directly compare these past storms with the Carrington Event, says Ilya Usoskin, a space physicist at the University of Oulu in Finland and a coauthor of the August study. The 1859 flare did not produce a particle downpour on Earth, so there are no carbon-14 counts to compare. But the 775 event appears to be one of the strongest solar particle storms recorded in the last 12,000 years, Usoskin says.

There is a catch, Hudson notes. Tree rings are laid down annually, so a few smaller flares within the span of several months might appear as one big event in the tree ring record.

But even then, any one of these smaller flares may still have been impressive. “Every one of those events would be at least on the order of three times as big as the Carrington Event in terms of its energy,” Cliver says.

That, however, is still modest compared with some other stars in our galaxy.

Super flares

If life does exist on the planet orbiting Proxima Centauri, it probably has a rough go of it.

“You really are looking at having something like a Carrington Event happening daily,” says Meredith MacGregor, an astrophysicist at the University of Colorado Boulder. Even stronger “super flares,” like the one she and colleagues spotted in 2019, may go off roughly every other day. Her team spotted that flare, possibly 100 times as powerful as the Carrington Event, after watching the star next door for just 40 hours.

With a near-constant barrage of flares, any atmosphere clinging to the rocky planet snuggled up close to the star would never have time to recover. “Yes, a Carrington Event [on Earth] would fry some electronics and would ruin GPS signals,” MacGregor says, “but it’s not going to destroy the habitability of our planet.”

To be clear, Proxima Centauri is not like the sun. It’s an M dwarf, a diminutive orb that glows red. And these tiny stars are famous for their oversized flares. But some sunlike stars can send up super flares as well.

This realization has come from telescopes in space designed to look for planets around other stars. NASA’s now-defunct Kepler telescope did this by looking for subtle dips in starlight as planets crossed in front of their suns.

Over four years, Kepler recorded 26 super flares — up to about 100 times as energetic as the Carrington Event — on 15 sunlike stars, researchers reported in January. NASA’s ongoing TESS mission, another space-based telescope hunting for exoplanets,  found a similar frequency of superflares on sunlike stars in its first year of operation.

The Kepler data imply that sunlike stars experience the most powerful of these flares roughly once every 6,000 years. Our sun’s most powerful eruption in that time span is an order of magnitude weaker — but could a super flare be in our future?

“I don’t think any theory has sufficient predictive capability to mean anything,” Hudson says. “The leading theory basically says that the bigger the sunspot, the greater the flare.” Sunspots mark where the sun’s magnetic field punches through its surface, preventing hot gas from bubbling up from below. The spot looks dark because it’s cooler than everything around it.

And that is one difference between the sun and its eruptive neighbors. Super flares seem to happen on stars with cool, dark spots far larger than ever appear on the sun. “Based on known spot areas, there would therefore be a limit,” Hudson says.

The intricacies of any star’s magnetic machinations — spots, flares, etc. — are still poorly understood, so tying all these observations into one cohesive story will take time. But the quest to understand all this might improve predictions about what to expect from the sun in the future.

Flares that are powerful enough to disrupt our power grid probably occur, on average, a few times a century, Love says. “Looking at 1859 kind of helps put it in perspective, because what’s happened in the space-age era, since 1957, has been more modest.” The sun hasn’t aimed a Carrington-like flare at us in quite a while. A repeat of 1859 in the 21st century could be disastrous.

Humanity is far more technologically dependent than it was in 1859. A Carrington-like event today could wreak havoc on power grids, satellites and wireless communication. In 1972, a solar flare knocked out long-distance telephone lines in Illinois, for example. In 1989, a flare blacked out most of Quebec province, cutting power to roughly 6 million people for up to nine hours. In 2005, a solar storm disrupted GPS satellites for 10 minutes.

The best prevention is prediction. Knowing that a coronal mass ejection is on its way could give operators time to safely reconfigure or shut down equipment to prevent it from being destroyed.

Building in extra resiliency could help as well. For the power grid, that could include adding in redundancy or devices that can drain off excess charge. Federal agencies could have a stock of mobile power transformers standing by, ready to deploy to areas where existing transformers — which have been known to melt in previous solar storms — have been knocked out. In space, satellites could be put into a safe mode while they wait out the storm.

The Carrington Event was not a one-off. It was just a sample of what the sun can do. If research into past solar flares has taught us anything, it’s that humanity shouldn’t be wondering if a similar solar storm could happen again. All we can wonder is when.

Lea en español

10.1146/knowable-091721-1

Christopher Crockett is a staff researcher for Knowable and a freelance science writer living in Arlington, Virginia. He is thankful for the sun but wouldn’t want to see it when it’s angry.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

Secession is here: States, cities and the wealthy are already withdrawing from America

Acts of secession are happening across the U.S. Vector Illustration/Getty Images

Michael J. Lee, College of Charleston

Rep. Marjorie Taylor Greene, a Republican from Georgia, wants a “national divorce.” In her view, another Civil War is inevitable unless red and blue states form separate countries.

She has plenty of company on the right, where a host of others – 52% of Trump voters, Donald Trump himself and prominent Texas Republicans – have endorsed various forms of secession in recent years. Roughly 40% of Biden voters have fantasized about a national divorce as well. Some on the left urge a domestic breakup so that a new egalitarian nation might be, as Lincoln said at Gettysburg, “brought forth on this continent.”

The American Civil War was a national trauma precipitated by the secession of 11 Southern states over slavery. It is, therefore, understandable that many pundits and commentators would weigh in about the legality, feasibility and wisdom of secession when others clamor for divorce.

But all this secession talk misses a key point that every troubled couple knows. Just as there are ways to withdraw from a marriage before any formal divorce, there are also ways to exit a nation before officially seceding.

I have studied secession for 20 years, and I think that it is not just a “what if?” scenario anymore. In “We Are Not One People: Secession and Separatism in American Politics Since 1776,” my co-author and I go beyond narrow discussions of secession and the Civil War to frame secession as an extreme end point on a scale that includes various acts of exit that have already taken place across the U.S.

GOP Rep. Marjorie Taylor Greene wants red and blue states to separate. Anna Moneymaker/Getty Images

Scaled secession

This scale begins with smaller, targeted exits, like a person getting out of jury duty, and progresses to include the larger ways that communities refuse to comply with state and federal authorities.

Such refusals could involve legal maneuvers like interposition, in which a community delays or constrains the enforcement of a law it opposes, or nullification, in which a community explicitly declares a law to be null and void within its borders. At the end of the scale, there’s secession.

From this wider perspective, it is clear that many acts of departure – call them secession lite, de facto secession or soft separatism – are occurring right now. Americans have responded to increasing polarization by exploring the gradations between soft separatism and hard secession.

These escalating exits make sense in a polarized nation whose citizens are sorting themselves into like-minded neighbhorhoods. When compromise is elusive and coexistence is unpleasant, citizens have three options to get their way: Defeat the other side, eliminate the other side or get away from the other side.

Imagine a national law; it could be a mandate that citizens brush their teeth twice a day or a statute criminalizing texting while driving. Then imagine that a special group of people did not have to obey that law.

This quasi-secession can be achieved in several ways. Maybe this special group moves “off the grid” into the boondocks where they could text and drive without fear of oversight. Maybe this special group wields political power and can buy, bribe or lawyer their way out of any legal jam. Maybe this special group has persuaded a powerful authority, say Congress or the Supreme Court, to grant them unique legal exemptions.

These are hypothetical scenarios, but not imaginary ones. When groups exit public life and its civic duties and burdens, when they live under their own sets of rules, when they do not have to live with fellow citizens they have not chosen or listen to authorities they do not like, they have already seceded.

Schools to taxes

Present-day America offers numerous hard examples of soft separatism.

Over the past two decades, scores of wealthy white communities have separated from more diverse school districts. Advocates cite local control to justify these acts of school secession. But the result is the creation of parallel school districts, both relatively homogeneous but vastly different in racial makeup and economic background.

Several prominent district exits have occurred in the South – places like St. George, Louisiana – but instances from northern Maine to Southern California show that school splintering is happening nationwide.

As one reporter wrote, “If you didn’t want to attend school with certain people in your district, you just needed to find a way to put a district line between you and them.”

Many other examples of legalized separatism revolve around taxes. Disney World, for example, was classified as a “special tax district” in Florida in 1967. These special districts are functionally separate local governments and can provide public services and build and maintain their own infrastructure.

The company has saved millions by avoiding typical zoning, permitting and inspection processes for decades, although Florida Gov. Ron DeSantis has recently challenged Disney’s special designation. Disney was only one of 1,800 special tax districts in Florida; there are over 35,000 in the nation.

Jeff Bezos paid no federal income taxes in 2011. Elon Musk paid almost none in 2018. Tales of wealthy individuals avoiding taxes are as common as stories of rich Americans buying their way out of jail. “Wealthier Americans,” Robert Reich lamented as far back as the early 1990s, “have been withdrawing into their own neighborhoods and clubs for generations.” Reich worried that a “new secession” allowed the rich to “inhabit a different economy from other Americans.”

Some of the nation’s wealthiest citizens pay an effective tax rate close to zero. As one investigative reporter put it, the ultrawealthy “sidestep the system in an entirely legal way.”

Spectators applaud after the Buckingham County Board of Supervisors unanimously votes to pass a Second Amendment sanctuary resolution at a meeting in Buckingham, Va., Dec. 9, 2019. AP Photo/Steve Helber

One nation, divisible

Schools and taxes are just a start.

Eleven states dub themselves “Second Amendment sanctuaries” and refuse to enforce federal gun restrictions. Movements aiming to carve off rural, more politically conservative portions of blue states are growing; 11 counties in Eastern Oregon support seceding and reclassifying themselves as “Greater Idaho,” a move that Idaho’s state government supports.

Hoping to become a separate state independent of Chicago’s political influence, over two dozen rural Illinois counties have passed pro-secession referendums. Some Texas Republicans back “Texit,” where the state becomes an independent nation.

Separatist ideas come from the Left, too.

“Cal-exit,” a plan for California to leave the union after 2016, was the most acute recent attempt at secession.

And separatist acts have reshaped life and law in many states. Since 2012, 21 states have legalized marijuana, which is federally illegal. Sanctuary cities and states have emerged since 2016 to combat aggressive federal immigration laws and policies. Some prosecutors and judges refuse to prosecute women and medical providers for newly illegal abortions in some states.

Estimates vary, but some Americans are increasingly opting out of hypermodern, hyperpolarized life entirely. “Intentional communities,” rural, sustainable, cooperative communes like East Wind in the Ozarks, are, as The New York Times reported in 2020, proliferating “across the country.”

In many ways, America is already broken apart. When secession is portrayed in its strictest sense, as a group of people declaring independence and taking a portion of a nation as they depart, the discussion is myopic, and current acts of exit hide in plain sight. When it comes to secession, the question is not just “What if?” but “What now?”

Michael J. Lee, Professor of Communication, College of Charleston

This article is republished from The Conversation under a Creative Commons license. Read the original article.

A Fresh, Flavorful Take on Family Dinner

(Culinary.net) If your family ever gets stuck in a dinner routine rut, it can feel like you’re eating the same recipes over and over again.

However, this fresh and unique recipe for Cuban Chicken with Salsa Fresca might inspire you to think outside the culinary box and give your family members the satisfactory flavor they desire at dinnertime. With fresh ingredients and a wholesome flavor, this meal is perfect to add to your dinner menu rotation.

The chicken is full of flavor and baked using multiple seasonings to create a Cuban-like taste. The salsa fresca, which is added on top of the chicken, is a tad sweet with grapefruit segments and juice, but also satisfying with jicama, onion, cilantro and jalapeno. It adds so much color to your plate, and all these flavors mash together for something unique and special.

To start, create the marinade for your chicken and let it rest to allow all those wonderful spices to do their jobs. Set it in the fridge for 30 minutes or more.

Next, it’s time to make the salsa fresca. Start by chopping red onion and jicama then add grapefruit and jalapeno to the mix. Add grapefruit juice, olive oil and, finally, cilantro. Stir well with a large spoon until everything is combined.

Once the chicken is baked, cut it and assemble. The final result is a juicy chicken breast with a sweet yet crisp salsa topping. The flavors in this dish harmonize together to bring you a bite you have likely never experienced before.  

This meal is also nutritious with fresh fruit and lean chicken, so it’s a meal almost anyone can enjoy, even if you’re on a healthy eating kick.

Find more recipes and family dinner ideas at Culinary.net.

Watch video to see how to make this recipe!

 

Cuban Chicken with Salsa Fresca

Servings: 5

• 1          cup grapefruit juice
• 2          tablespoons olive oil
• 2          teaspoons garlic powder
• 2          teaspoons cumin
• 2          teaspoons paprika
• 1          teaspoon crushed red pepper
• 1 1/4    pounds boneless, skinless chicken breasts

Salsa Fresca:

• 1          cup grapefruit segments
• 1/2       jicama, cubed
• 1/2       red onion, chopped
• 3/4       cup grapefruit juice
• 4          tablespoons olive oil
• 1/2       cup fresh cilantro, chopped
• 1          jalapeno pepper, chopped

1. Heat oven to 400 F.
2. In large bowl, mix grapefruit juice, oil, garlic powder, cumin, paprika and red pepper until combined. Add chicken to bowl and turn to coat. Refrigerate 30 minutes or longer.
3. To make salsa fresca: In medium bowl, mix grapefruit segments, jicama, red onion, grapefruit juice, olive oil, cilantro and jalapeno pepper until combined. Refrigerate until ready to serve.
4. Remove chicken from marinade. Place chicken in baking dish. Bake 25-30 minutes until chicken is cooked through.
5. Serve chicken with salsa fresca.

SOURCE:
Culinary.net

A new history for the tropical forests of the Americas

Fossilized leaves and pollen are revealing the evolutionary past of New World tropical forests. The findings are helping to reshape predictions of what might happen to these ecosystems as the climate changes.

By Pablo Correa

In northern Colombia, in a semi-desert region that juts into the Caribbean Sea, its dusty roads traveled by the Wayúu people with their blankets and colorful backpacks, is Cerrejón — one of the largest open-pit coal mines in the world. Excavated for more than 30 years, its huge craters and twisted paths down which the trucks descend give the impression of a tropical hell.

But for the trained eyes of Carlos Jaramillo, that hell is a paradise he always dreamed of finding. There, while working for the Colombian Petroleum Institute more than 20 years ago, Jaramillo, a paleontologist and pollen expert, began with other colleagues to unearth the lost history of the Neotropical forests of the Americas — and to challenge some of the paradigms of paleontology.

Fossil after fossil, these scientists have been reconstructing a history that was thought to be impossible to discover. “For many years, it was believed that almost no fossils had been preserved in the tropics because of the high rates of weathering — the decomposition of minerals and rocks — and, if they did exist, it would be very difficult to find them because of the current forest cover,” says Jaramillo, now a researcher at the Smithsonian Tropical Research Institute in Panama.

While the geology textbooks that Jaramillo and his colleagues learned from said that tropical forests, just like temperate forests, had remained more or less stable in their plant composition for at least 120 million years, recent palaeobotanical findings suggest a very different story.

For the entire Cenozoic, the current geological era that began some 66 million years ago with the meteorite impact that wiped out dinosaurs and many of the planet’s other species, “the climate and geology of the Neotropics have been far from stable,” note ecologist Christopher W. Dick and botanist R. Toby Pennington in a review of the history and geography of Neotropical tree diversity in the 2019 Annual Review of Ecology, Evolution, and Systematics. In addition to the meteorite impact, which marked a before and after in this ecosystem, the rise of the Isthmus of Panama, the formation of the Amazon River and the uplift of the northern Andes, for example, have profoundly influenced the region’s climate, species formation and migration.

But the precise association between these events is unclear. The pieces of that story are what a new generation of scientists has set out to find.

Messages within the pollen

A key piece in reconstructing the history of tropical forests has to do with pollen grains, which contain the male sex cells of most plants and trees; these function like nature’s clock. They are so tiny that, to study them under the microscope, some paleobotanists like to use cat’s whiskers to manipulate them. The wall that covers a pollen grain is quite resistant to temperature changes, helping its preservation for millions of years inside the rocks. And the pollen is so abundant that, although most of it is destroyed, some remains in the geological layers, waiting for a palynologist to set eyes on it. Its virtues do not end there. The shape of pollen is so diverse — circular, triangular, hexagonal, with tiny spikes or warts — that it is equivalent to a fingerprint for plants.

The first fossil signs of the evolution of tropical flora came from the work of palynologists who, in the second half of the 20th century, traveled the Neotropics alongside oil explorers. Their pollen samples and classifications, which helped them to identify potential oil exploration sites, remained far from the gaze of other scientists due to commercial interests.

One of Jaramillo’s studies, together with paleobotanist Paula Mejía Velásquez, now with Leeward Community College in Hawaii, consisted of reviewing two such cores. Drilled by ExxonMobil in the region of Los Mangos, the samples remained ignored for decades in the National Rock Library of the Colombian Petroleum Institute. The cores, some 600 to 700 meters long, contained a pollen chronology that spanned the early Cretaceous, some 120 million years ago, to the present. And within them, the scientists found a powerful reason to continue their research into that remote past: The flowering plants, or angiosperms, which today comprise more than 96 percent of the Neotropical forest, were less than 7 percent at the beginning of the Cretaceous.

“There, I had a logical place to start,” Jaramillo says. “The story I wanted to study is how we went from an ecosystem where there were almost no angiosperms to a forest with 96 percent angiosperms. That is the story of a fundamental change in an ecosystem.”

It is easy to forget how crucial flowering plants are to the survival of so many animal species, including us, wrote paleobotanist Peter Crane, former director of the Field Museum in Chicago and the Royal Botanic Gardens, Kew, in London, in 2010: “Angiosperms provide the energy on which most of the rest of biological diversity depends. The evolution of flowers and flowering plants is therefore both of fundamental significance and of contemporary relevance.”

Charles Darwin himself, in a very famous letter to his friend Joseph Hooker, described the relatively late and apparently sudden appearance of flowering plants as “an abominable mystery.” This abrupt arrival was contrary to his postulates on evolution, according to which changes occurred gradually. In the letter written in July 1879, three years before his death, he commented that he would “like to see this whole problem solved.”

Around 2002, when Jaramillo was working for the Colombian Petroleum Institute, a pair of fossil-loving geology students, Fabiany Herrera and Edwin Cadena — more enthusiastic than well-trained in paleontology — joined the fossil hunt to help unravel the whole story of the Neotropical forests’ past.

Herrera, now assistant curator of paleobotany at the Field Museum, followed Jaramillo’s advice and traveled to Cerrejón to look for a ghost: fossil leaves from the early Cenozoic. In pits up to 2 kilometers in diameter that had been abandoned by the miners, with a geological hammer in hand, smashing one rock after another, Herrera unearthed a palaeobotanical treasure trove: more than 2,000 fossil plants.

Cadena, the other student who had joined the adventure, turned his attention to other residents of those archaic forests. Cerrejón held many hidden surprises: fossils of turtles, crocodiles and giant snakes. In 2009, for example, the remains of a snake measuring 12.8 meters and weighing approximately 1,135 kilograms were discovered there. Named Titanoboa cerrejonensis, it crawled through these ecosystems some 58 million to 60 million years ago, according to the report on the discovery published in Nature. Fossils of these and other animals offer clues about the conditions in these past habitats.

“My role has been to understand how animals, particularly reptiles, relate to these ecosystems and to validate the conditions of temperature, precipitation and other characteristics that we deduce,” explains Cadena, a paleontologist at the Rosario University in Bogota. For example, in the case of a snake like the Titanoboa, its size would require a minimum average annual temperature of 30 to 34 degrees Celsius to survive.

“That feeling of hopelessness, that in the Tropics nothing is preserved, that we would not find the fossils we needed, began to disappear with the visits to Cerrejón,” says Jaramillo.

In the decades that followed, other researchers joined the effort to rewrite the history of Neotropical forests. The exploration sites also expanded: Magdalena River Valley, the Ecuadorian and Colombian Amazon, central Peru, and parts of Argentina and Chile. In 2009, when the Panama Canal expansion began, the researchers took advantage of this new window into the geological depths to continue gathering clues to the past of the forests.

The great impact

The fossil evidence that Jaramillo and his colleagues have collected over three decades, at some 50 sites in the Tropics, is providing a better understanding of how and when these cathedrals of biodiversity — the most species-diverse ecological communities in the world — were formed. It has also made it possible to outline how the varieties of plant and animal species has changed; and how they transformed and reacted to the great extinction caused 66 million years ago by the impact of a meteorite in the Yucatan Peninsula that left the Chicxulub crater. With the power of close to a billion bombs of the size dropped on Hiroshima, it led to the extinction of about 76 percent of all marine species and 40 percent of the genera present on the planet at that time.

What were the forests like before and after that impact, a chapter of history known to geologists as the K/Pg boundary, the boundary between the Cretaceous and the Paleogene?

Analysis of 6,000 fossil leaves and 50,000 pollen grains collected from 46 sites — including, of course, Cerrejón, as well as coal mines in central Colombia and the Amazon — have revealed a snapshot of forests 66 million years ago.

In those forests where dinosaurs roamed, a more equitable community of plants lived together. The space was distributed among ferns (50 percent), flowering plants (40 percent) and trees such as araucarias and conifers. The flora did not form the tangled, layered structure of the Neotropical forests today. Light filtered down to the ground, unblocked by the jungle canopy we see today, explains Mónica Carvalho, a paleobotanist and curator at the Museum of Paleontology at the University of Michigan, who with Jaramillo led a study, published in 2021 in the journal Science, that summarizes these findings.

Another difference that these fossils tell us of was a lower contribution, to the atmosphere, of water released by plants. For a paleobotanist like Carvalho, this can be deduced from the length, thickness and patterns of the veins stamped on a fossil leaf, since they provide clues about the metabolism of these plants. And the bites imprinted on these fossil leaves reveal other forest inhabitants — insects — and their ecological interactions. While the insect communities that inhabited these forests before the great extinction were more specialist — one type of insect feeding on one specific type of plant — the post-extinction insects are more generalist: You see the same kinds of damage or bites on almost every plant.

Only after the meteorite did legumes, capable of capturing — or fixing — nitrogen from the air, become as abundant as they are today, which would explain profound changes in soil fertility. However, all this radical change in plant composition was a slow process. After the meteorite, it took at least 7 million years for the forests to recover and surpass the degree of plant diversity present before the impact.

“Thanks to this, we now know that, although flowers diversified in the dinosaur era, they took longer to come to dominate the forest, and that evolutionary opportunity arose for them, thanks to the ecological catastrophe unleashed by the asteroid,” says Carvalho.

Why were those pre-impact forests different from today's forests? In the Science article, Carvalho and colleagues pose three possible answers to that question. A first hypothesis suggests that herbivorous dinosaurs exerted control over the forest; with their disappearance, the ecosystem balance was broken. The second hypothesis refers to the nutrient composition of the soil, which is suspected to have been less fertile before the cataclysm. The ashfall after the Chicxulub impact changed the balance of minerals, providing, for example, more phosphorus. A third hypothesis raises the possibility of a selective extinction that affected conifer lineages — which inhabited smaller ecological ranges — more than angiosperm lineages, which found an opportunity to expand.

“The whole story that this data tells us is incredible,” Jaramillo says. “To know that the forest of today is the product of a precise instant, millions of years ago, of a particular minute, is fantastic.”

Forests and climate change

Beyond understanding the dramatic changes these forests underwent after the Chicxulub meteorite impact, the study of their past is also allowing scientists to decipher how the Neotropical forests have reacted to changes in temperature and higher CO₂ levels, data that may provide clues about what may happen to these ecosystems in the face of global warming.

One answer lies in the Eocene, which began 56.3 million years ago when a phenomenon known as the Paleocene-Eocene Thermal Maximum (PETM) occurred. This short-lived global warming event, the fastest in the last 140 million years, involved a global temperature increase of 5 to 7 degrees Celsius over 10,000 to 50,000 years, Jaramillo describes in one of the chapters of the book The Geology of Colombia. This is the best analog to modern human-induced warming, except that the PETM developed slower than today’s warming, allowing many species to adapt. It occurred because of volcanism in the North Sea, which led to the addition of some 1,300 ppm of CO ₂ to an atmosphere that previously had averaged 500 ppm of CO ₂.

“Although plants can migrate to higher latitudes to escape warming, extinctions in the Tropics would be expected, as the temperature would stress plants beyond their survival limit,” says Jaramillo. But what Jaramillo and his colleagues found when they analyzed the fossil record from three sites in northeastern Colombia and northwestern Venezuela was quite different. As mean annual temperature increased (by between 3.5 and 5 degrees Celsius) during the PETM, in the northern lowlands of the Neotropics, “the rate of origin of new species doubled, while extinction rates remained unchanged.” This increase in temperature resulted in 30 percent more diverse vegetation. Epiphytic ferns, typical of Neotropical forests, and orchids and leaf-cutter ants also took advantage of the energetic bonanza of more CO₂, and greater diversity was observed among them.

Jaramillo believes that these results contradict global paleoclimatic models that predict a collapse of Neotropical vegetation due to heat stress. In an article he coauthored in the 2013 Annual Review of Earth and Planetary Sciences, he noted that in a compilation of 5,998 empirical estimates of temperature over the past 120 million years, “the Tropical Rain Forest did not collapse during past warmings; on the contrary, its diversity increased. The increase in temperature seems to be a major driver in promoting diversity.”

Does this mean that, contrary to apocalyptic forecasts, Neotropical forests could experience a biological bonanza during today’s global warming? Not necessarily. The speed at which humans are causing the accumulation of greenhouse gases is different from that of the PETM, which developed more slowly. Jaramillo says it is not possible to know whether plants under the current scenario would be able to adapt given the sheer speed of change.

However, for Jaramillo, there are signs for optimism — at least regarding the fate of plants. “The genes that regulate photosynthesis are deeply rooted in plant phylogeny and we would expect the physiological function to be similar in Eocene and present-day plants,” he says. In other words, modern plants carry in their DNA the genetic variability to cope with increases in temperature and CO ₂, he notes, “as long as there is enough water in the soil. Water, then, is the key factor to consider in the tropical biomes of the future.”

“Of course, as all good research does, it also begs some further questions,” says Crane, now president of the Oak Spring Garden Foundation, of the work of Jaramillo and his colleagues. Many of these questions, Crane adds, are related to the evolution of flowering plants: What was happening in the late Cretaceous before the meteorite? What was the vegetation like? How did angiosperms evolve before the meteorite impact, before they dominated the forest? Which groups were involved and what kind of ecological communities did they create? And how did those communities take the forest from having essentially no flowering plant trees to having a great variety of flowering plant trees?

But the most urgent and dramatic of the questions on Crane’s list is how forests will react to the unusual changes in global climate that we humans are causing. No one has a definitive answer. What we do know is that plants conquered this planet 470 million to 500 million years ago. We know that 430 million years ago, they caused an explosion of diversity and shaped the biosphere by reducing atmospheric CO ₂ by eight to 20 times. We know that they have survived five mass extinctions, including the one caused by the meteorite.

Plants have always found a way to survive, as Jaramillo explains. On this planet, the inexperienced and new ones are we humans, who appeared less than 300,000 years ago, on one of the smaller branches of the tree of life.

Article translated by Debbie Ponchner

Lea en español

Pablo Correa is a Colombian science journalist and former science, environment and health editor of the Colombian newspaper El Espectador. He was a Knight Science Journalism Fellow at MIT in 2012-2013. He is the author of the book Rodolfo Llinás, la pregunta difícil. Follow him on Twitter @pcorrea78.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.