Some types of air pollution slow global warming — but at the cost of millions of deaths a year.
“The smoke is very thick, like a dark mushroom in the sky,” said reporter Gus Abelgas in a 1991 television broadcast on the ongoing volcanic eruption of Mount Pinatubo in the Philippines. “It’s just like what we saw in Hiroshima.”
After 500 years of dormancy, Mount Pinatubo’s June explosion represented one of the largest volcanic events of the 20th century. The eruption forced approximately 30,000 indigenous Aeta people to evacuate the nearby area and killed over 200 people. (An additional 426 people died in the three months following the explosion due to poor conditions in the evacuation zones.)
The eruption also sent a sulfuric gas cloud into the atmosphere 28 miles high — or five Mount Everests stacked on top of each other. While almost a foot of muddy ash covered the surrounding area, the sulfuric gas mixed with water vapor in the air, creating a layer of a reflective acidic compound that cooled the Earth for two years.
Yes, that’s right: A hot volcanic eruption made the planet cooler.
Sulfur dioxide is one of many aerosol particles that reflects the sun’s light and can act to make temperatures globally cooler than they would be otherwise. Mount Pinatubo’s eruption temporarily dropped global temps by about 0.9 degrees Fahrenheit. That doesn’t sound like a huge jump, but if you were to warm the planet by an additional 0.9 degrees Fahrenheit today, that could trigger increased flooding and fire events, sweeping heat waves, super storms, and even famines.
Collectively, volcanoes around the globe emit 20 to 25 million tons of the cooling aerosol sulfur dioxide annually, but in 1991, Mount Pinatubo alone released 15 million tons of the compound. And while extreme, Mount Pinatubo’s cooling effect is not an anomaly — nor are volcanoes the only sources.
Air-polluting sources — such as volcanic eruptions, wildfires, and industrial factories — all emit particles that reflect light and cool the planet. To be absolutely clear: This is not at all to say that air pollution is a good thing. Air pollution, after all, contributes to 7 million premature deaths per year globally. Improving air quality should be a top goal across the planet.
“Many of those same human activities [that contribute to climate change] can increase air pollution in the form of particles, and those particles are both detrimental to health and counteract, to some extent, the warming that comes from greenhouse gasses,” said Jason West, a professor in environmental sciences and engineering at the University of North Carolina at Chapel Hill.
But in the absence of cooling aerosols, we might have nearly 1 degree Fahrenheit more warming, experts say. Given the world is on track to record its hottest summer on record, this is bad news. While the positive effects of temperature-cooling pollution do not outweigh air pollution sources’ greenhouse gas emissions or the overall cost of these pollutants to human health, they have acted to somewhat slow the rate of warming. As we reduce air pollution — which we must do — we need to be prepared for the short-term consequences of even faster global warming.
The relationship between climate change and air pollution
Greenhouse gas emissions — such as carbon dioxide, methane, and nitrous oxide — warm the planet by absorbing light and therefore trapping heat. Electricity production (which has soared over the last few decades) and vehicles are some of the largest producers of these gasses.
Some aerosol particles — such as sulfate aerosols, particulate matter, and sea salt — prevent warming. Heat dances off bright-colored particles and is absorbed by darker particles (like soot and black carbon). Bright, reflective aerosol particles affect Earth’s temperature by scattering sunlight in the upper part of the atmosphere, the stratosphere. They also create and brighten clouds (which then also reflect light away from the Earth’s surface) by attracting water vapor that attaches and sometimes freezes on the particles. The conglomeration of water vapor prompts the formation and thickening of clouds.
Natural sources, such as volcanoes, sea spray, and desert storms, can shoot these particles into the atmosphere. Human-made sources, like the burning of coal, also emit aerosols. Vehicles and power plants emit sulfate and nitrate particles.
While greenhouse gas emissions can persist in the atmosphere for decades or even centuries, cooling aerosol particles live in the atmosphere for only days or weeks due to their composition and climate conditions. Particle size and temperature influence these emissions’ atmospheric lifespan. As Mount Pinatubo demonstrated, the effect of cooling aerosol particles is temporary (in the case of this massive volcanic eruption, the aerosol effect was felt for approximately two years) but they can be very strong. After the far larger eruption of Mount Tambora, 1816 became known as “the year without a summer,” as temperatures dropped by as much as 7 degrees Fahrenheit around the world, crops failed, and tens of thousands of people died from hunger.
In 2018, researchers from the Center for International Climate and Environmental Research, NASA, the University of Leeds, the University of Oxford, and Climate Analytics found that ending the emission of greenhouse gasses will also end human-caused aerosol emissions. The absence of these aerosols will result in global heating and increased rain, especially in locations where aerosol emissions were once regularly emitted. The world must prepare for a temporary spike in warmth in order to address the even more dangerous long-term effects of climate change and air pollution.
If human-caused air pollution disappeared this instant, the world would experience the negative warming consequences of past greenhouse emissions for decades to come, with virtually no lingering cooling effect from the previously emitted particles, said West.
“Let’s say we emitted greenhouse gases, CO2, and [aerosol cooling] particles at the same rate forever. Eventually, the greenhouse gases are going to win because they’re going to continue to accumulate,” he said. “Whereas the particle concentration would stay the same because it’s short-lived.” Ultimately, aerosol particles have masked some of greenhouse gasses’ effects, but they won’t do so forever.
Why we need cleaner air
Despite evidence that keeping cooling aerosol particles from polluting sources would prevent some level of global warming, doing so is not an option. One, because they share a source with greenhouse gasses, and two, because they are unequivocally detrimental to human health.
Air Quality Index (AQI) levels are used to measure the level of air pollution and range between 0 to 500. Even at relatively moderate levels (101-150 AQI), air pollution causes eye and throat irritation. But, as the intensity and length of exposure increase, so do the consequences.
PM2.5, a type of fine-particle pollutant, is one of the most harmful air pollutants to human health currently regulated by the Environmental Protection Agency, and exposure to high levels can cause heart attacks, strokes, and severe respiratory problems, and even initiate the onset of chronic conditions such as bronchitis and asthma. The effects are particularly dangerous for those suffering from preexisting lung and heart conditions like obstructive pulmonary disease.
“All the things we know that cigarette smoking can cause, like cardiovascular disease and lung cancer, likewise, fine particles do that,” said Patrick Kinney, a professor of urban health for Boston University’s School of Public Health. “Of course, we don’t breathe as much [fine particles] as a cigarette smoker does … but it’s the same kind of effect.”
Infants and children are particularly susceptible to developing cancers and cognitive impairments due to air pollution. Low- and middle-income countries, primarily in Asia and Africa, account for more than 90 percent of these deaths.
“When we look over the planet, aerosols can have a different influence,” said West. “We expect aerosols to have a bigger effect in the Northern Hemisphere — where most of the pollution sources are — compared to the Southern Hemisphere, which is relatively more pristine. It’s covered by ocean and there’s much less population.” Two-thirds of the African continent and most of Asia lie in the Northern Hemisphere.
Vehicle exhaust and coal combustion contribute to particularly severe air pollution in densely populated areas within Asia. China and India, the two most populous countries in the world, emit over half of the world’s PM2.5 emissions, and in both countries, air pollution contributes to the deaths of more than 2 million people a year.
“We need to switch away from fossil fuels toward renewables,” said West, “which has benefits for both air pollution and for the climate.”
What will happen to global temperatures?
If humans keep burning fossil fuels, air pollution will worsen, and so will climate change. Consequently, a warmer planet will make our air quality worse. Hot weather creates the perfect conditions for the reactions that produce ozone (a greenhouse gas). And heat waves can cause droughts. During a drought, forest fires, which produce particle pollution, are more common. “Air pollution affects climate change and climate change affects air pollution,” said Kinney.
But air pollution is not the only — or most important — byproduct of climate change, he added. Global warming will bring a host of other problems, including extreme heat waves, hurricanes, wildfires, and the proliferation of infectious diseases.
“This is not new. We’ve had storms always and we’ve had heat waves always,” said Kinney. “But what climate change is doing is making those extremes more extreme, and pushing the sort of upper tail of the extreme distribution for temperature and also for storm intensity.”
Across the world, natural disasters, including extreme winter storms, wildfires, and flooding, are wreaking havoc on communities that previously never faced such events. “It’s worse than a new normal. I call it a new abnormal,” Michael Mann, a climate scientist at the University of Pennsylvania, previously told Vox.
Preventing further climate change is, therefore, the greatest concern, and given greenhouse gases and aerosol cooling particles often stem from the same sources, it’s very difficult to isolate the emissions.
“There are some particles that are warming, such as black carbon particles. They have a warming influence, as well as being bad for health,” said West. “So if we can target black carbon-related emissions, then we could have a benefit for both problems — for both air pollution and health, and for climate. But … many sources are sources of both black carbon and cooling aerosols.”
Even if the warming and cooling pollutants had different sources, the health outcomes from aerosol particles — heart attacks, strokes, chronic diseases — mean keeping them around isn’t a viable option.
Thus, scientists and researchers are now looking for ways to mimic the cooling aerosol effect without the same negative impact through a practice known as geoengineering. This field encompasses methods meant to offset the impacts of climate change by influencing the environment.
One geoengineering method involves injecting salt particles into the air to brighten and increase cloud coverage over the ocean. Despite research dating back to 2012 showing that salt particles cannot slow climate change at a meaningful rate, researchers continue to explore the idea.
A number of other ideas have been proposed and tested, including producing artificial clouds and placing mirrors in space. Producing clouds would entail shooting sulfur dioxide (the same stuff Mount Pinatubo spat out) into the atmosphere, but initial studies of the practice showed that starting and then stopping the method could lead to dire unknown effects. The consequences of space mirrors seem less deadly but are also less understood, and embarking on such a program would cost trillions of dollars. All of these approaches are also politically contentious.
While none of these methods is ready for wide-scale use, interest in geoengineering is rising. In late June, the Biden administration released a report indicating the White House is open to geoengineering research aimed at cooling the planet, specifically the “scientific and societal implications of solar radiation modification.” No concrete plans or policies in this field have yet been made, indicating a level of necessary caution given concerns about geoengineering’s little-understood ramifications.
Altering the delicate balance of the Earth’s climate system through intentional intervention carries inherent risks, including crop and wildlife die-offs and unintended shifts in weather patterns. Some methods could create massive droughts in some parts of the world, or even deplete the ozone layer further.
Another concern is “termination shock.” If geoengineering technology went into effect and was then abruptly ended (by choice or by unpredictable events like terrorist attacks or natural disasters) then the resulting warming would be even more significant and catastrophic than current projections.
Additionally, given that one country’s decision to engage in a geoengineering method could have global repercussions, scientists and policymakers continue to debate the political repercussions and oversight of this technology.
And before any of these ideas can come to fruition, scientists and researchers must develop a better understanding of the true impact of the aerosol cooling effect.
“We know that aerosol particles that come from human emissions have the potential to have a cooling effect on climate,” said Casey Wall, a postdoctoral researcher studying climate science at the University of Oslo. “And we know it can offset some of the warming effects from human greenhouse gas emissions. But the really big debate right now in the climate research community is just how much that aerosol cooling effect offsets the warming from greenhouse gases.”
Air pollution’s relationship with and on climate change is complex, but at the end of the day, cleaner air will lead to a healthier planet. “Air pollution as we commonly talk about it is a bad thing overall, even though it has this effect of cooling the climate,” said Wall. “The effects on human health overall outweigh that.”
Parents can have a great relationship with their kids without being their friend.
When it comes to raising children, there is no shortage of platitudes: “Parenting doesn’t come with an instruction manual,” “It’s a lifetime job,” “Children are always listening.” One question that endures in modern parenting culture is one about the relationship between parent and child — should you be friends with your kid?
Part of the issue is the vagueness of the question: What does friendship with a child actually look like? Does being friends with your kids mean simply having fun together, or does it signify a relationship of equals? The American Psychological Association defines friendship as “a voluntary relationship between two or more people that is relatively long-lasting and in which those involved tend to be concerned with meeting the others’ needs and interests as well as satisfying their own desires.” Parenting, however, isn’t voluntary, and a child shouldn’t be interested in meeting their parents’ needs.
As parenting style has shifted away from “children should be seen and not heard” toward a family dynamic where children’s voices and opinions are valued, a tension remains regarding the balance between parental authority and childhood inclusivity. “There’s been a lot of movement in terms of what role do children play in the family dynamic,” says Francyne Zeltser, the director of mental health and testing services Manhattan Psychology Group. “With children having more of a voice and having an opinion, how does that change the parent-child dynamic?”
While experts stress the importance of a warm and supportive relationship with children, parents must maintain authority over their kids, which is directly at odds with the ideals of friendship. At its core, friendship is elective and equal. Once you’re a parent, there’s no opting out, making friendship not exactly appropriate for parents and their kids. So, should parents be friends with their little ones? In short: No. But you can still maintain aspects of friendship while remaining in the driver’s seat with little ones.
Think about your parenting style
There are four styles of parenting in the child psychology field that inform the relationship parents have with their kids: authoritarian, authoritative, permissive, and uninvolved. On opposite ends of the spectrum are uninvolved parents — absent and withdrawn — and authoritarian — demanding, strict, “my way or the highway.” In the middle are permissive parents, who are very loving but don’t enforce rules, and authoritative parents who set expectations and hold their children accountable, but explain their reasoning.
“A parent that was ‘friends’ with their child would likely have more of a permissive parenting style,” Zeltser says, “where they would more likely go to great lengths to ensure that their child is happy, they would probably avoid conflict whenever possible. They might accommodate their child’s requests even if they’re not necessarily in agreement with their child’s requests to avoid disappointing their child. Those types of themes align much more with friendship than with a parent.”
An authoritative parenting style, Zeltser says, is one that includes compromise and shared decision-making — the hallmarks of friendship — but with the adult holding the power to enforce rules. When children are younger and need more guidance and routine, there will be fewer negotiables; parents have the final say on bedtime, eating vegetables, or when it’s time to come home from a friend’s house. But it’s important to explain to kids why you’re making these decisions, Zeltser says.
When parents are too lenient, they risk never teaching their children to hold themselves accountable and that there are consequences to their actions, says Carrie Cole, the research director for the Gottman Institute and a certified Gottman therapist.
Being authoritative doesn’t mean unloving
Acting as a friend to kids undermines a parent’s authority, says Kenneth Ginsburg, the founding director of the Center for Parent and Teen Communication, because a child may have a fear of disappointing you. Because friendship is conditional, companions may reject one another and end the relationship for any reason at all. For this reason, children may avoid coming to their parents for help because they don’t want to be rejected for doing something they perceive as wrong or bad. “The reality is that during adolescence, friendships can readily change and we worry so much as adolescents about not fitting in, or disappointing or losing our friends,” says Ginsburg, also the author of Congrats — You’re Having a Teen! Strengthen Your Family and Raise a Good Person. “When we place our parents in that category, then we’re not going to use them in the way we really need to. Instead, we understand that parents are in a whole different category than friends. It’s guaranteed that they will stand by you.”
Being accessible to your kids doesn’t mean dressing like them or only having fun together, Ginsburg says; it’s showing up for them when they’re having a disagreement with a friend or when they’re feeling overwhelmed with school and still loving them. Parenthood, rather than friendship, means never pushing them away or withholding love.
Set clear rules and expectations with children — but keep them involved
Another crucial difference between friendship and parenting is, in friendship, both parties agree on a set of unspoken rules. Parents, on the other hand, should call all the shots with their kids, experts say. However, this doesn’t mean you can’t value your child’s opinions and wishes when it comes to those rules and expectations, says Wendy Grolnick, a professor of psychology at Clark University. “We call it autonomy support with structure,” she says. “Having structure, having some rules, some expectations, some guidelines. … [Parents] having some authority, but also supporting kids feeling like they have a say, like they’re active, they’re respected, their opinions count and get taken into account for real as you problem-solve together.”
In studies, Grolnick found that when parents were very strict and regimented with their kids when it came to homework and study time, chores, and other personal responsibilities at home, kids were more resistant to following their parents’ orders. However, in relation to safety — telling parents where you’ll be during unsupervised time, respecting curfew — kids were more accepting of concrete rules. “Kids are much more tolerant about parents setting the rules in areas that they see as areas of safety and morality,” Grolnick says, “versus things that they think are in their personal purview.”
Instead of telling kids they can’t play video games until their homework is done, Grolnick suggests asking your child, “Let’s talk about what makes sense in terms of when homework should be done” and then give them choices. If you’d ideally like their homework to be completed before dinner time, ask your child when they’d prefer to do it: right when they get home from school or after they have a snack? “You listen to their opinion, you joint problem-solve, then you give them some choices about those rules and expectations,” Grolnick says. Parents should have the final say on some topics — for example, that homework is completed, or to treat others with respect — but all children, regardless of age, deserve some level of autonomy, Grolnick says, with the goal to make their choices age-appropriate.
Remember, parents need boundaries with their kids, too
In an effort to relate with their children, some parents may fail to set boundaries or reinforce rules out of fear of upsetting their child, Cole says. But moments of disappointment can be learning opportunities for a kid. If a younger child is upset when you tell them it’s time to leave the park, help them identify those emotions. Cole suggests saying something like, “Yes, it makes sense that you would be disappointed that we have to go home now.”
“Then we need to help them come up with some way to problem-solve,” Cole says. What is something your child is looking forward to when they get home? Or perhaps you can make a plan to go back to the park after school in a few days.
Setting and sticking to boundaries can be made easier by explaining why you’re making certain decisions, Zeltser says. There needs to be a clear reason beyond “because I’m the grown-up and I said so.” For example, if your child is frustrated when you ask them to clean up their toys, explain why, says Kei Nomaguchi, a professor of sociology at Bowling Green State University.
Be upfront with your children about your plans for the day so there are no surprises: Try saying, “We’re going to the park for two hours and then we’re going home for lunch.” That way, if you run into your kid’s friend in the park whose parents ask if your family would be interested in joining them for a meal, your child isn’t disappointed when you mention you already had alternative plans — or your kid is pleasantly surprised if you change your mind. “Now all of a sudden, the child’s reality exceeds their expectation,” Zeltser says. “They were thinking they were going to have to go home, now they could stay and spend more time with their friends. Now they’re elated.”
Sometimes, when parents are divorced or separated, they’ll do whatever it takes to be liked by their children, Ginsburg says, and become more lax with rules or denigrate the other parent. “The message that kid is hearing is, oh my gosh, if I displeased this person, they might reject me too,” he says. Keep your children separate from the adult relationships, and the emotions that come with adult problems (regardless if divorce is involved) and don’t tell them anything you wouldn’t want them repeating to friends.
Parents may also have the impulse to overshare with their children and to let them in on everything that’s going on. This may give the child a false impression that they sometimes need to take care of their parents, emotionally, Cole says. Even with teenagers, there needs to be a strong separation between the adult’s personal and parenting roles. For example, parents should not discuss their dating or sex life with their kids, no matter the child’s age, even if there is heartbreak involved. “The child should not be taking care of the parents in that way,” Cole says. Seek out the counsel of a trusted adult friend or mental health professional instead.
All told, boundaries help kids maintain a routine, which is what they need, Nomaguchi says. “Too much freedom for kids is not really great for the family routine, and also family relationships, that seems to be what studies tend to show,” she says.
As children age into adults themselves, you won’t need to have as much authority over your kids and their routines, and so you can adopt a relationship that veers closer toward friendship. However, when children are living at home, parents should stay in charge of the big-picture choices, but allow decisions to be largely collaborative. This helps kids feel like they have an ally in their parents, but — crucially — not a friend.
An extreme heat wave has pushed Florida’s reef to the brink — and burned up years worth of progress.
PICKLES REEF, FLORIDA — As soon as our boat reached the reef, the problem appeared. Looking down through the clear, turquoise water, I saw a handful of stark white patches on the seafloor, some 20 feet below.
I strapped on a tank, leapt into the ocean, and sank down near one of them. It was a large cluster of elkhorn coral, a threatened species that looks a bit like studded moose antlers sprouting from the reef. Normally, elkhorn is a vibrant, golden brown. Here it was bone white, a sunken skeleton.
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Jennifer Adler
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Jennifer Adler
As I cruised along Pickles Reef, which isn’t far from Key Largo, more species of corals came into view. Some looked like tree branches; others resembled spindly fingers that moved with the current. All of them were white. It was as if the reef had been dusted with a fresh coat of snow — beautiful, but haunting.
In the world of coral biology, white is a bad color. It indicates that the corals, which comprise a colony of marine animals called polyps, have lost a kind of algae that lives within their bodies. Those algae give the corals most of their food and their brilliant color in exchange for nutrients and a place to absorb sunlight. White, or “bleached,” corals aren’t dead; they are starving to death.
The bleached corals I saw that afternoon at Pickles are a small part of a massive, ongoing tragedy: Across the Florida Keys and throughout much of the Caribbean, coral reefs have bleached and many of them are dying. Some of these starving corals are literally centuries old. Others were planted recently to revive the reefs, and their bleaching represents a devastating setback for coral restoration.
The culprit is extreme heat.
In the last three months, a marine heat wave has been cooking the Caribbean, breaking down the relationship between coral and those symbiotic algae. Some shallow buoys in South Florida registered temperatures in excess of 100 degrees in July — about as warm as a hot tub. And for weeks on end, reefs in the Florida Keys, the largest coral reef in the continental US, were soaking in 90-plus degree water. That’s well beyond the threshold for bleaching in this region.
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Coral Reef Watch/NOAA
“I’ve never seen anything like this in this area, period,” said Ian Enochs, a coral biologist at the National Oceanic and Atmospheric Administration, who’s been monitoring Florida’s reefs for more than a decade.
This mass bleaching event has made an already bad situation worse. Well before summer, the area of healthy reefs in the Florida Keys had already declined by 90 percent, due to past heat waves, diseases, ocean acidification, and other threats. The majority of Florida’s reefs that remain, meanwhile, are eroding.
And the consequences of these declines are severe. Coral reefs function like seawalls, helping limit life-threatening storm surge during hurricanes; they’re the engine of the region’s tourism economy; and they provide a home to as much as a quarter of all marine life including fish that people eat.
The long-term outlook for coral reefs brings more bad news. As our cars and factories continue to blanket the Earth with carbon dioxide, heat waves will become more common and intense. Top climate scientists have warned that warming could wipe out 70 to 90 percent of the tropical coral reefs worldwide. This is not just a problem in Florida. It’s a problem everywhere.
This raises a difficult question: Does Florida’s reef — and coral reefs in similar dire situations around the world — have a future on our planet?
That afternoon in September wasn’t the first time I visited Pickles. I dived here in April of 2022 for a very different kind of story — one of hope.
At the time, underwater photojournalist Jenny Adler and I were documenting local efforts to restore Florida’s ailing coral reefs. Restoration is akin to tree planting: Groups like the Coral Restoration Foundation grow fragments of coral on structures in the open ocean, which they then “plant” on degraded reefs with an underwater adhesive. The effect is similar to planting saplings in a degraded forest — it gives the reef new life.
Diving in Pickles that spring, we saw large colonies of staghorn and elkhorn corals that CRF had planted a few years earlier. These older corals, which are both threatened species, had grown from small fragments into colorful, meter-wide structures. They were healthy and helped form a reef, shown below, like those that appear in postcards.
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Coral restoration was working, I thought. People were hopeful. Florida’s reefs were starting to grow back. It was a rare conservation victory.
Then came July.
Here’s how the same location looks today. (The green tint on the corals below is algae that grows on colonies when they die. This is different from the good algae within healthy coral tissue).
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“It’s heartbreaking,” said Roxane Boonstra, the dive training administrator at CRF who took us diving at Pickles earlier this month. “I’ve been working in the coral field for what feels like my whole life and I’ve never seen bleaching on this scale.”
In the last decade, CRF has planted more than 43,000 pieces of coral on Pickles. Since July, many of them have bleached or died, including nearly all the coral we saw.
While Florida’s coral reefs have bleached several times before, this event is nonetheless historic. “We’re looking at a heat stress event that is in excess of two times greater than anything that’s ever been experienced in Florida on record,” Derek Manzello, a coral reef ecologist at NOAA, told me in August. Temperatures in South Florida were not only the warmest on record, but the heat started earlier and lasted longer than it did during past bleaching events, Manzello said.
And it’s not only coral colonies in Florida that are suffering. Several other countries in the Caribbean and Latin America have also reported bleaching this summer including Mexico, Belize, and Puerto Rico. Many local communities in these regions are highly dependent on coral reefs for food or for work. “We’re talking about thousands upon thousands of miles of coral reefs undergoing severe bleaching heat stress,” Manzello told reporters in mid-August.
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Jennifer Adler
Some reefs in the Keys are much worse off than others, especially those that are shallow. On a warm weekday morning, we boated out to a reef off the coast of Key West called Eastern Dry Rocks. It’s one of seven sites that are part of Mission: Iconic Reefs, a multimillion-dollar effort involving NOAA, CRF, and other groups to resurrect reefs in this region.
After a smooth 20-minute ride, we suited up and dropped down to the bottom, 15 feet below. Bailey Thomasson, who leads restoration here for CRF, toured us around, showing us coral after coral that her team had planted. Some were small, about the size of a hand; others stretched a couple of feet above the reef.
They were nearly all dead and coated in algae or bone white and bleached. It was as if a white plague had spread across the reef.
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I did see a handful of neon green and blue corals, which popped against the monochrome reef. This was a good sign, I thought. But back on the boat, Thomasson explained that they, too, were bleached. Some corals produce bright pigments that function as sunscreen to protect themselves (and possibly to also attract those important algae partners that they lost). What I saw wasn’t a healthy color — it was a sign of dire stress.
Seeing all this bleaching is not only gut-wrenching, but it also points to an obvious challenge with restoration: Organizations are putting corals into an ocean that’s killing them.
This challenge is not lost on researchers.
“Restoration as we currently do it is not working in Florida,” Enochs of NOAA told me. “The fact that we are putting out corals that are ultimately just going to die is, in my opinion, irresponsible.”
This doesn’t make restoration pointless, several scientists told me. It just underscores the need to do it a bit differently.
Our dives weren’t all bleak. A large patch of staghorn coral at Pickles looked healthy. It was an orangey beige and its tentacles were poking out (coral polyps are a bit like sea anemones with stinging tentacles around a mouth). Elkhorn corals in CRF’s coral nursery, where the group raises corals to plant, were colorful and healthy, too, resembling pieces of fried chicken dangling from PVC and fiberglass structures.
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Jennifer Adler
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Jennifer Adler
This is key: Some coral colonies tolerate heat better than others.
Why? Research has shown that thermal tolerance among corals is, to an extent, genetically based, and resistance to other threats like disease may be rooted in their DNA, as well. And it’s this fact that underlies the future of coral restoration. Scientists essentially want to plant corals on the reef with underlying genetics that give them a leg up.
One way they do this is by helping corals breed and produce coral babies. It’s a numbers game: The more genetically distinct babies you have, the more likely it will be that some of them are tolerant to extreme heat, disease, or other threats.
This approach is important in a place like Florida, where the reef is so damaged that corals have trouble breeding on their own. Corals breed by spawning: Once a year, a set number of days after a full moon, colonies puff out bundles of sperm and eggs (or just sperm or eggs, or in some cases, larvae). In order for the eggs of one individual to be fertilized, they have to encounter the sperm of another. But there are so few healthy corals in Florida that their spawn often don’t meet.
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Jennifer Adler
That’s where self-described “coral baby doctor” Hanna Koch comes in. A scientist at the Mote Marine Laboratory and Aquarium, Koch, who’s both serious and prone to laughter, coaxes coral parents into spawning in giant tanks on land. She and Celia Leto, a staff biologist, use that spawn to produce genetically diverse coral babies — nearly invisible to the naked eye — which Mote will eventually plant on local reefs.
The idea here is that some of those babies will survive extreme heat or other stresses and give rise to the next generation. “We are restoring our reef with corals that have the best possible chances of surviving and coping with continued environmental stress,” Koch told me.
This approach produces a diverse crop of babies with varied traits. But scientists can also breed corals for a single trait, such as heat tolerance, in the same way that a farmer might breed fruits to make them sweeter. This method is known as selective breeding.
Breeding two corals that can survive extreme heat tends to produce babies that also have built-in heat tolerance. What’s more, scientists can breed algae symbionts — the organisms that live inside healthy corals — to be more heat tolerant, as well. “It’s like bartending,” Kate Quigley, a coral ecologist, said of selective breeding corals. “You’re just mixing things in different proportions.”
A researcher at Australia’s Minderoo Foundation, Quigley has shown that it’s possible to selectively breed some corals and their algae to withstand slightly higher temperatures over a few weeks, potentially increasing the survival of corals by 26-fold when oceans warm up. Other research has shown that even if just one parent has a higher heat tolerance it will produce more thermally tolerant babies.
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Jennifer Adler
Selective breeding may sound great, but it has some major limitations. For one, the process is slow and hard to scale up; corals take years to grow and reach a size where they can spawn. Plus, you can only tweak a coral’s traits by so much. “There is a hard ceiling to the biology,” Quigley said. Researchers may be able to stretch the coral’s heat tolerance by a few degrees, but it almost certainly won’t be enough for them to cope with future heat waves.
That brings us to the biggest problem of all: Even the most advanced restoration efforts are only temporary solutions. They’re just buying time. The only true solution, roughly a dozen experts told me, is for countries and companies to quickly ramp down their carbon emissions. Even then, aggressive restoration will still be needed to help reefs hold on.
“People will criticize restoration, asking why we are throwing millions of dollars at this effort that’s going to fail,” Boonstra of CRF said. “Well, it’s only going to fail if you think that this is all that’s needed. All we’re trying to do is keep things alive until other people take the big hard steps that are necessary.”
By the time Jenny and I arrived in Florida, the water had cooled down from the summer peaks by several degrees. It was in the mid-80s — near the upper limit of what corals can tolerate. Yet it’s still hot. And even if the water does cool down, as it should as the year progresses, recovering corals can still be prone to disease and struggle to reproduce.
So where does that leave the Florida Keys? Is it doomed?
It will be months before researchers do a full assessment of this summer’s bleaching. Some deeper reefs, and those farther north, are better off and may have avoided bleaching, scientists say. But in the short term, it’s not looking great.
Over the long term, as heat waves intensify, it’s unlikely that coral will disappear altogether. Some species are hardier, such as a type of soft coral called sea fans; they’re important to wildlife but don’t build reefs in the same way as hard corals. Ultimately, it’s just a question of what future reefs will look like — degraded, and providing little value to humans and marine animals, or full of life and beauty, as they once were.
“I think it’s likely that reefs are going to persist in the future,” said Liam Lachs, a doctoral researcher at Newcastle University who has studied heat tolerance in corals. “The question is, what’s the composition of the reefs? Do they still provide the services that they had historically provided?”
For now, even in its bleached and dying state, parts of the reef are still holding on.
Around 9:30 pm on a clear night, Jenny and I were gearing up to dive on Looe Key, another spot with substantial bleaching. This was a critical moment: We were here to see if any wild corals on the reef would spawn, perhaps leading to a new generation of corals with new genetic diversity.
It felt like a long shot. Corals only spawn once a year for a few minutes, typically in the middle of the night, and they’re unlikely to reproduce if they’re bleached or otherwise stressed out. To see spawning here would be “miraculous,” said Koch, who was with us that night, “given the scope and scale of degradation and devastation.”
At night underwater, sea critters that are typically hiding during the day come out. A 4-foot stingray cruised the seafloor under the beam of my flashlight. Lobster antennae poked out of dark crevices. A small moray eel, its mouth wide open, waited for a hapless fish to swim by. Dozens of henchmen-like barracudas lurked above me.
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Jennifer Adler
Hovering in pairs next to healthy corals, we waited, our bodies rising and falling with every breath. When our air ran low, we popped up to the surface, switched out our tanks, and swam back down.
Now it was around 10:30 and we were on our third dive of the night. The water around us sparkled with bioluminescent critters. Then I saw a light flashing frantically a few meters away. I swam over to find Koch and Leto staring closely at a large mound of a knobby brown coral. They pointed ecstatically.
With all of us in a circle around the coral, the show began. Section by section, the colony — a species known as lobe star coral — began to expel little pink balls, like an upside down salt shaker. They hovered above the coral for a second before getting swept away by the current.
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Jennifer Adler
In each of those balls were several eggs and millions of sperm. If all goes well, they’ll drift around the ocean until they cross paths with the sperm and eggs of another coral that also spawned that night. Together, they’ll produce coral larvae that will swim to the ocean floor and start a colony of their own, creating the next generation of coral in the Florida Keys — assuming it’s not too hot for them to thrive.
Jennifer Adler contributed reporting.