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In this two-hour special, renowned paleontologist Kirk Johnson takes us on an epic adventure through time at the polar extremes of our planet. Following a trail of strange fossils found in all the wrong places—beech trees in Antarctica, hippo-like mammals in the Arctic—Johnson uncovers the bizarre history of the poles, from miles-high ice sheets to warm polar forests teeming with life. What caused such dramatic changes at the ends of the Earth? And what can the past reveal about our planet’s climate today—and in the future? (Premiered February 5, 2020)

Paleontologist Kirk Johnson explores the dynamic history—and future—of ice at the poles.

Polar Extremes

Something big is happening to Earth’s climate, and the polar regions hold the key to understanding it. Join top scientists on the hunt for clues that tell a surprising story about our planet’s past...and preview where we might be headed.

The Polar Lab

Disastrous hurricanes. Widespread droughts and wildfires. Withering heat. Extreme rainfall. It is hard not to conclude that something’s up with the weather, and many scientists agree. It’s the result of the weather machine itself—our climate—changing, becoming hotter and more erratic. In this two-hour documentary, NOVA will cut through the confusion around climate change. Why do scientists overwhelmingly agree that our climate is changing, and that human activity is causing it? How and when will it affect us through the weather we experience? And what will it take to bend the trajectory of planetary warming toward more benign outcomes? Join scientists around the world on a quest to better understand the workings of the weather and climate machine we call Earth, and discover how we can be resilient—even thrive—in the face of enormous change.

Discover how Earth’s intricate climate system is changing.

Decoding the Weather Machine

Koch Foundation

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Coral Reef Restoration Through Assisted Evolution I Reef Rescue

Learn about the impact of rising ocean temperatures on coral reefs and how selective breeding in the lab may help corals survive in these videos adapted from NOVA: Reef Rescue.

The Symbiotic Relationship Between Coral and Algae I Reef Rescue

Learn how rising water temperatures affect corals and their symbiotic algae in these videos adapted from NOVA: Reef Rescue.

Coral Reefs Help Protect Coastlines I Reef Rescue

Learn about the protective role of coral reefs along coastal areas in this video adapted from NOVA: Reef Rescue.

A long exposure shows insects drawn to a halogen street light in the city of Mazatlán, Mexico. Image Credit: Matt Mawson, Getty Images

Why light pollution is a solvable environmental crisis

It’s not easy to make street lights exciting, but Kelly Beatty is trying. Holding court over Zoom on a spring evening in 2021, he warns citizens of Nantucket island in Massachusetts that the decisions they’ll soon make about their lights are choices they’re “going to have to live with for a long time.” Beatty often helps advise communities like Nantucket as they transition their streetlights from traditional bulbs to more energy-efficient LEDs, or light-emitting diodes. As communications officer of the Massachusetts chapter of the <a href="https://www.darksky.org">International Dark-Sky Association</a> (IDA), he’s well aware of the stakes. As this process has been repeated in towns across the world, it has led to a new and preventable environmental problem. LED lights can last 20 years or more, he reminds the group. “It’s important to get it right when you have a chance.”
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The IDA defines light pollution as the inappropriate or excessive use of artificial light, with variations including glare (excessive brightness that causes visual discomfort), skyglow (brightening of sky over inhabited areas) and light trespass (light that falls where it isn’t intended or needed). Already a growing problem, light pollution has intensified with the rise of LEDs, which produce blue-intense light in shorter wavelengths that are more susceptible to scatter and thus travel farther. An estimated 99% of U.S. and European populations now live under light-polluted skies, and one third of humanity is unable to see the Milky Way at night. From marine life and plants to birds and insects, the loss of darkness has left deep scars in our ecosystems.Twenty-five miles off the coast of Massachusetts, Nantucket is one of the darkest places left on the Eastern Seaboard—but even its skies are lightening. As they fight for their darkness, many Nantucketers taking up the cause see light pollution as the rare environmental threat where individual people can make a real difference. “It’s easier to solve than many of the other serious problems we have on Nantucket,” like erosion or affordable housing, says Gail Walker, founder of the local activist organization <a href="https://nantucketlights.org">Nantucket Lights</a>. “If we can educate people and help them understand the problems, most people are going to get on board.”
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<img alt="Silhouette of tree at night with city light behind and Milky Way in the sky" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/Nantucket_tree_at_night.width-990_CwescF7.jpg"/>
<figcaption>The night sky as seen from the Middle Moors on Nantucket. Image Credit: Bill Hoenk Photography
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The problem of light pollution started in earnest with the widespread installation of streetlights, which coincided with the rise of highways in the 1950s and 60s. “Think about society then: Everything closed at 8 or 9, and they rolled up the sidewalks,” Beatty says. “We did not have a 24/7 society like we have now.” With highways came all-night gas stations, drug stores, and grocery stores. And, above all, streetlights by the tens of millions. Then, in recent decades, lightbulbs made with LEDs arrived, a revolution in energy efficiency with seemingly little downside. After all, an LED bulb <a href="https://www.energy.gov/energysaver/led-lighting">converts some 90%</a> of the electricity it uses into light, whereas a conventional incandescent bulb only converts about 10%. And LED bulbs are touted as lasting up to 25 times longer.But the physics of LEDs make them fundamentally different from incandescents. While those traditional bulbs put out warm white light made of all colors mixed together, LEDs filter blue-rich light through a specialized phosphor material, producing light that appears white to the human eye but is still more blue-intense than incandescents’ light.But blue light is also the most disruptive to our nighttime environment because it mimics daylight, disrupting the hormone production and sleep cycles of both animals and humans. Melatonin, one of those hormones, helps the immune system destroy renegade cells dividing out of control. That can lead to other health issues, including heightened rates of cancer. And, “we’re not the only ones who produce melatonin,” says Mario Motta, a cardiologist and trustee of the American Medical Association. “Even amoebae produce melatonin”—meaning even amoebae might be vulnerable to light at night. 
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<img alt="Two geckos inside a lit up street lamp at night" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/GettyImages-1287021220_I8ybJf2.width-990_QaqcLnK.jpg"/>
<figcaption>Two geckos in an outdoor lamp in Córdoba, Spain. Studies indicate that insect predators like bats, lizards, and toads will station themselves near artificial lights, where they can easily pick off prey. Image Credit: Clemente Crisci / EyeEm, Getty Images
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The impacts of light pollution are evident everywhere from human health to astronomy research, but they come into particular focus in the recent phenomenon of global species die-offs. Between 100 million and a billion birds die every year due to light pollution, according to Massachusetts IDA chapter president James Lowenthal. New York City recently dealt with a huge die-off, “with flocks of migratory birds slamming into buildings,” says Sarah Bois, an ecologist at the island’s <a href="https://llnf.org">Linda Loring Nature Foundation</a> and a member of Nantucket Lights. “They’re attracted to light.” A 2015 study at New York’s 9/11 “Tribute in Light'' installation showed an increase from 500 birds within half a kilometer of the light beams before they were turned on to 15,700 just minutes after.The issue is a double whammy for birds because they rely on insects for food—and those populations are plummeting, with <a href="https://www.smithsonianmag.com/smart-news/light-pollution-contributes-insect-apocalypse-180973642/">light pollution contributing</a> significantly to the so-called “insect apocalypse.” By some estimates, one third of insects attracted to light sources at night die before morning, either due to exhaustion or because they get eaten. And according to a study in Germany, the number of insects in that country alone that die after being attracted to lights can number 100 billion or more in a single summer. Some starve to death searching for food that should appear bluer at twilight but is lit up amber under streetlights, says insect conservationist Avalon Owens, a doctoral candidate at Tufts University. Some are thrown off by light just the way we are, because of their circadian rhythms. Pollinators whose schedules are altered by artificial light miss the flowers they’re evolutionarily paired with, if the flowers naturally close and open with the warmth of the sun. And insects that rely on circadian rhythms for their yearly development don’t hibernate in time for winter and freeze to death.On Nantucket, these phenomena are of particular concern because the island is home to a remarkably healthy population of northern long-eared bats, which are endangered. Like many birds, the bats rely on insects for food and are easily dazzled by light, putting them in increasing jeopardy. Jack Dubinsky, director of the Maria Mitchell Aquarium on Nantucket, says he’s concerned that adding increasingly lit-up nights to the challenges of climate change, water quality, and ecosystem collapse could put huge pressure on some already struggling species. “The more curveballs we throw, the less likely they’ll be able to find their way,” he says.
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<img alt="Satellite image of U.S. at night, cities lit up" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/Light_pollution_US_map.width-990_FtftHWY.jpg"/>
<figcaption>A composite of nighttime images taken by the Suomi National Polar-orbiting Partnership satellite in 2012 shows light pollution in the contiguous United States. Image Credit: NASA Earth Observatory
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For Beatty, the first step in addressing the issues wrought by light pollution—and LEDs in particular—is to look at color temperature, which is measured in kelvins. Lower temperatures like 2,000 K correspond to warm reddish or yellowish light (think candlelight) while higher color temperatures like 4,500 K and up correspond to harsher, bluer light (think blue sky). “When LEDs started getting rolled out for streetlights, the most common ones were very close to this native, blue-rich light,” since they were also the most energy efficient, Beatty says.But because the white light of most LED bulbs is produced by coating a blue-intense LED in phosphor material, it’s possible to switch out that phosphor for one that absorbs and re-radiates the light to be less blue and look warmer, using the same technology already common in fluorescent bulbs. A new wave of LEDs, known as PC Amber, have color temperatures as low as 2,200 K and are gaining popularity.Beatty also points to another solution built into LED technology. Beyond being highly efficient, LED bulbs “can be controlled in amazing ways, programmed with central computers,” he says. Cities like Cambridge, Massachusetts, have programmed their LED streetlights to reduce to 50% power at various points during the night, depending on the street. A few towns in Europe have opted for motion-sensing lights that turn on and off as needed. Older-style lighting worked best if left on continuously through the night, Beatty says. But “LEDs don’t mind being turned on and off or dimmed up, down sideways, multiple times per second,” he says. “You can do anything you want to them.”
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In 2012, the American Medical Association <a href="https://www.mariomottamd.com/wp-content/uploads/AMA-Health-Effects-Light-at-Night.pdf">declared light at night carcinogenic</a>, which has helped drive policy change in cities across the country. New York City drew criticism from the IDA when it began replacing its streetlights with LED bulbs, some at color temperatures as high as 4,000 K, but changed tack when residents complained, citing the <a href="https://www.mariomottamd.com/wp-content/uploads/CSAPH_Report_02-A-16.pdf">AMA guidance</a>. (It helps that high-color-temperature lights are “universally hated,” Beatty says.) Since then, initiatives like Audubon’s Lights Out New York have also convinced managers of major structures like the Chrysler Building to go dark from midnight to dawn during the fall bird migration season. And the city has <a href="https://gothamist.com/arts-entertainment/how-nyc-audubon-helps-birds-disoriented-tribute-light-911">reached an agreement</a> to turn off for short periods the 9/11 memorial lights that were leading to so many avian deaths, allowing the trapped birds to continue their journey.In Chicago, which was famous in light pollution circles as the most over-lit city in the country, the city has been gradually replacing its streetlights with 3,000 K LEDs, which it  touted as saving the same energy as taking 2,400 cars off the road. Tucson, Arizona, reduced its lighting emissions by 60%, in part by switching to 3,000 K LEDs and programming them to dim late at night. And in fall 2021, Pittsburgh passed the nation’s first <a href="https://skyandtelescope.org/astronomy-news/pittsburgh-goes-dark-could-this-new-dark-sky-ordinance-begin-a-trend/">dark sky ordinance</a> that will involve replacing both its older-model conventional streetlights and more recently installed high-color-temperature LEDs with warmer, fully shielded lights equipped with motion sensors.
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<img alt="Teh city of phoenix glows yellow under a night sky" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/GettyImages-200547640-001.width-990_eBLDkCh.jpg"/>
<figcaption>Phoenix, Arizona, illuminated at night. In 1988, two astronomers noticed the brightening glow of nearby Tucson, Arizona, was threatening the dark skies at Kitt Peak National Observatory. They were "the first ones to raise the alarm about light pollution,” Kelly Beatty says. Image Credit: Andy Ryan, Getty Images
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Beatty encourages concerned citizens to get involved with local conversations about light at night—both about streetlights and policies around new construction. “The time to be proactive is when developments are being proposed,” he says, since it’s much easier to convince developers to make changes to their lighting plans when the buildings aren’t already set in literal stone. “Most times people install bad lighting because they don’t know any better,” he says. “It just takes one person to say ‘Hey, there’s another way to do this.’” That’s one reason he came to Nantucket’s meeting about streetlights.“We find the people most concerned about light pollution are not big cities but in rural areas,” he adds. And in that observation he sees a powerful advantage in the fight for dark skies. Since the causes of light pollution are hyperlocal, changes made by individuals and small groups can make a quick and observable difference, which empowers them to continue that work. “Every place where we can energize and educate local citizens is a victory, however small,” he says. “There are hundreds of people like me across the U.S. who are advocates for this, who insert themselves into local situations where education is desperately needed.”Gail Walker had already been watching Nantucket’s brightening skies when she learned about the IDA and its mission. The vivid stars over empty, windswept beaches had always been one of her favorite things about the island, and she wanted to preserve that experience for her grandchildren. Walker has earned a reputation locally as a go-getter, a retired attorney with a knack for bringing people around to her point of view. After coordinating the March 2021 forum on light pollution with Beatty, she began work in earnest with Nantucket Lights, bringing together concerned citizens to raise awareness and shape the community’s response.From there, conversations on the island evolved quickly. Walker began advising homeowners associations about their lighting policies, connecting local groups with lighting experts, and helping assess citizen complaints about lighting issues. She is also shepherding the community’s planned application to become an official International Dark-Sky Community.To be fair, Nantucket has a few key factors that give it an advantage in these efforts: a law governing outdoor lighting already on the books, an affluent community with an interest in maintaining a certain ambience on the island, and officials who see the benefit of that ambience for tourism. But to Walker, a significant part of her success so far is that light pollution “is a solvable problem.” Unlike other issues, which might seem too big, complex or intractable, she says, “there’s kind of an easy fix.”  Motta and Beatty suggest starting with the <a href="https://www.darksky.org/our-work/lighting/lighting-principles/">five principles</a> the IDA has established toward what Motta calls “sane outdoor lighting,” guidelines that individuals can follow to make better lighting choices in their own homes. Those guidelines include an emphasis on light that is useful, or toward a purpose; and targeted, or directed only where it's needed and otherwise properly shielded. Lights should also be no brighter than necessary. And it’s best to avoid high-color temperature, bluer light as much as possible. “That’s it,” Motta says. “Follow those simple rules, and we’ll have a much better world.”Owens, the entomologist, agrees. When it comes to adjusting our night light to help insects, “The most important thing is to ask, ‘Are you using the light?’” she says. “ If not, don’t have it.” She’s a proponent of flashlights, motion detectors, and timers, all the gadgets that might help keep light inside a building. “Automated curtain technology is the next big thing,” she jokes. “Who’s against closing your curtains? Nobody, but it’s hard to remember.”
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<img alt="The Milky Way extends straight up above an observatory dome" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/MilkyDome2.width-990_MGZpnNG.jpg"/>
<figcaption>The Milky Way stretches above the Maria Mitchell Association's Loines Observatory in Nantucket, Massachusetts. Image Credit: Charity Grace Mofsen
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On a breezy fall evening with a nip in the air, Nantucket’s <a href="https://www.mariamitchell.org">Maria Mitchell Association</a> is hosting about 50 visitors on the small platform between the domes of its observatory’s two telescopes—both currently trained on Jupiter to allow observers to admire its stripes. Overhead, clouds glide by soundlessly, reflecting a glow from the north that marks a grocery store and cluster of brightly lit schools. “You can see how they’re reflected up above, leaking up into the sky,” association Director of Astronomy Regina Jorgenson says, pointing. The distant light from Cape Cod is even visible occasionally, she says, on humid nights when moisture in the atmosphere scatters light farther.Still, in breaks in the mist, she’s able to point out the sugary trail of the Milky Way. The upturned faces of tonight’s crowd reflect awe at the sight. Many island visitors have never seen the Milky Way before. “The first time they see it, it’s a transformative experience for them,” she says.Jorgenson has been involved with the observatory since her internship here in 1997 and, along with her astronomy research, is dedicated to preserving the legacy of Maria Mitchell. Mitchell, America’s first professional woman astronomer, was born on the island in 1818. She gained fame for discovering a comet and became the first woman to be inducted into the American Academy of Arts and Sciences. Almost a century later, an NSF-funded internship at the observatory has become a key source of support for female astronomers in the U.S. Jorgenson is determined to protect that resource—and the dark sky that makes it possible. Watching the night grow inexorably brighter over the decades from her observatory perch outside town has been “scary” she says, but she remains hopeful. Nantucket’s geography, history, and culture makes so many things possible, she says. “We’re a small enough community that we have power to make a quick and effective change.” Correction: Nantucket is roughly 25 miles off the coast of Cape Cod, not 12 miles as previously stated.
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Excessive outdoor lighting is deadly to animals and takes a toll on human health and wellbeing, too. But when it comes to large-scale environmental problems, this one may be a relatively easy fix.

Flooding Farmland Eastern Va Farmers Navigate Sea Level Rise

Farming has been a part of life and business around coastal Virginia for centuries. But now farmland is gradually succumbing to the rising seas.
Farmers are watching their land flood and crops die as the region experiences the fastest average rate of sea level rise on the Atlantic coast. It’s making them question whether agriculture will be a sustainable source of income in the future.This video was produced in collaboration with NOVA and is made possible in part by the Corporation for Public Broadcasting, a private corporation funded by the American people.
Flooding Farmland Eastern Va Farmers Navigate Sea Level RisePublished: March 31, 2022Sam Turken: Farming has always been a part of coastal Virginia’s economy especially around the Eastern Shore. The climate isn’t too hot or cold and the soil’s fertile. But now the region is experiencing the fastest average rate of sea level rise on the Atlantic coast. Water levels around Southeast Virginia have risen nearly 20 inches over the past century and it’s estimated they could go up about seven feet by 2100.So what does all this mean for coastal farmers around here? Lynn Gayle is still figuring that out. Lynn Gayle: This is a seaside farm in an area called Fox Grove and the barrier islands are about a mile to the east of us. My son farms with me and we tend about 2,500 acres. Farming is a lifestyle.Sam Turken: Gayle has farmed out here for more than three decades. He grows commodities—corn, soybean, and something called rapeseed, which produces an oil used for engines and plastics.Gayle shows me around a 75-acre field bordering the ocean. Lush soybean crops are everywhere except for one small patch close to the water. Lynn Gayle: They were planted here, and you can actually see the salt residue on the soil. Most of those that came up died. Occasional high tides or flood tides or if there&#x27;s a nor&#x27;easter this would be underwater right here.Sam Turken: So if I stick my finger in this salty patch... will it taste like salt?Lynn Gayle: Yup.Sam Turken: It&#x27;s like pure salt.Gayle says he&#x27;s watched the seawater encroach farther and farther up this field over the past decade. About an acre is no longer farmable.  It&#x27;s even worse at another field he used to plant. 20 acres completely failed.This is all worrying Gayle&#x27;s 32-year-old son, Sands. He grew up playing with tractor toys. Now he&#x27;s taking over the business and says hundreds of thousands of future dollars are at stake.Sands Gayle: A third of the acreage that I farm could be right on the water and directly affected by sea level rise. And as it takes more area, then, of course, I&#x27;m going to have to figure something out.Sam Turken: Nationwide, only the Gulf Coast around Texas and Louisiana is experiencing a faster rate of rising seas. As oceans heat up from climate change, water molecules expand, contributing to sea level rise. Another part of the problem...Scientists point to low elevation combined with sinking land around the Gulf and Virginia. The land is subsiding because we’ve pumped out water from underground.The last Ice Age thousands of years ago is also playing a role. Cora Baird studies sea level rise around here for the University of Virginia&#x27;s Coastal Research Center.Cora Baird: Essentially, when there was the last glaciation, and there were ice sheets down this way, when the ice sheets are really heavy because they&#x27;re a lot of water and they essentially push the crust of the Earth down.Sam Turken: This region was at the end of the glacier and actually lifted, kind of like when you sit on a mattress, the part beneath you sinks but the area around you bulges up. Those glaciers melted away thousands of years ago but the Earth’s crust is still reacting.Cora Baird: Now we are still doing the process of settling down as if whoever was sitting on the mattress just stood up.Sam Turken: On top of this, as glaciers continue to melt all over the world, they’re sending more water into the oceans. Add all of it up and it&#x27;s not a question of if some areas will go under water, but when.Up and down this narrow peninsula, Baird speaks to farmers concerned about the rising seas.Cora Baird: This was land that was farmed from the 1650s until the early 2000s, when the farmers stopped renewing their leases because the land was getting wet and buggy.Sam Turken: Baird shows me what could happen when saltwater takes over farmland. Cora Baird: What we’re seeing is the regrowth of species including some salt marsh species. So, like the dark green shrubs that are poking out between the grass, that&#x27;s a salt associated shrub, that&#x27;s the wax myrtle.Sam Turken: Baird says the water isn&#x27;t just coming in from the ocean, rivers, and creeks. It&#x27;s rising from beneath the land, mixing with groundwater and making the soil wetter and saltier. An invisible killer. It’s a threat all the way down the Atlantic Coast to Florida. Sam Turken: Does it make you sad that this is happening?Cora Baird: If you feel like it&#x27;s important to continue farming, and it&#x27;s important to keep agriculture a part of our, our sort of landscape and identity where we&#x27;re in such a confined geographical area, if it keeps pushing in from the edges, there&#x27;s only so many places we can shift to.Sam Turken: Now, there are ways that farmers could hold on for some time. Salt can dehydrate plants to death or even poison them. So researchers are testing salt-tolerant crops like barley and quinoa. Farmers also can dig ditches and build berms to keep water away. How did the farmers&#x27; market go yesterday?Thelonius Cook: Oh, it wasn&#x27;t too bad.Sam Turken: Planting wetlands and trees around fields is another option. Thelonius Cook: So what I&#x27;ve started to do on my landscape is plant things that love the water. They love wet soils. And they can actually help to soak up some of that water.Sam Turken: Thelonius Cook runs a sustainable produce farm. No fertilizer or pesticides. Problem is the farm is right along the main highway on the Eastern Shore. So when it rains, a lot of water flows off the road onto Cook&#x27;s fields.Thelonius Cook: There is so much investment in this, this land into this farm. Right now, a lot of us are just treating the symptoms, but not the main problem and the problem is the climate change issue that&#x27;s, that&#x27;s causing the sea levels to rise in the first place.Sam Turken: This has killed enough crops the past few years to translate into a $30,000 loss. Cook, who&#x27;s 42, hopes to adapt to the rising water, but he says there&#x27;s a good chance farming here could become impossible.Thelonius Cook: It makes you feel deflated because, you know, you&#x27;re building something you know, for the next generation, and you want to make sure that this is here for the next generation.

Farming has been a part of life and business around coastal Virginia for centuries. But now farmland is gradually succumbing to the rising seas.

A house on stilts in Nags Head, North Carolina surrounded by high tide surf. Image Credit: John Greim/LightRocket via Getty Images

A major Atlantic current is at a critical transition point

Around 15,000 years ago, the Earth began to transition from a state of heavy glacial coverage to a period of warming. As temperatures rose, large ice sheets that once blanketed much of North America and Europe thawed, and the oceans began to rise.But after 2,000 years of warming, the Earth abruptly cooled to near-glacial conditions. And it stayed that way for more than a thousand years.Scientists have long debated how this abrupt climatic event, which they call the <a href="https://www.ncei.noaa.gov/sites/default/files/2021-11/3%20The%20Younger%20Dryas%20-FINAL%20NOV%20%281%29.pdf">Younger Dryas</a>, occurred. This question has become an urgent one as some researchers think an abrupt climatic event could happen again and disrupt the Gulf Stream, the forceful ocean current that transports warm water from the Gulf of Mexico up North America’s Northeast coast.
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An <a href="https://static1.squarespace.com/static/614dece04ec1fe659b8317d5/t/616354b99fa33305c8a8e81b/1633899707925/Observation-based.pdf">analysis</a> published in the journal Nature Climate Change in August found that the larger system that the Gulf Stream is part of, called the Atlantic Meridional Overturning Circulation (AMOC), is approaching a tipping point. Over the last century, this ocean circulation system has “moved closer to a critical threshold, where it may abruptly shift from the current, strong circulation mode to a much weaker one,” says study author Niklas Boers, a climate researcher at the Potsdam Institute for Climate Impact Research in Germany. Should the AMOC weaken substantially, it could bring intense cold and stronger storms to Europe, raise sea levels across the northeast coast of North America, and disrupt the flow of <a href="https://earthobservatory.nasa.gov/global-maps/MYD28M/MY1DMM_CHLORA">vital nutrients</a> that phytoplankton, marine algae that make up the foundation of the aquatic food web, need to grow in the North Atlantic."It’s important to acknowledge just how big of a system we are trying to measure,” says Nicholas Foukal, a physical oceanographer at Woods Hole Oceanographic Institute who was not involved in the study. “If you calculate the flow of all of the rivers in the world, the amount of water is only about 1% to 2% of the Gulf Stream.”The AMOC is an Atlantic section of a global conveyor belt that drives surface and deepwater currents in every ocean, and influences the rate of sea ice formation at the poles. The AMOC has exhibited two states: a strong, stable state and a slow, weak one. Warming temperatures weaken the AMOC, the new analysis suggests, ultimately pushing it toward a tipping point where it could rapidly turn off.
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<img alt="This map of the Atlantic shows the direction the Gulf Stream travels as it transports warm water north from the equator" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/gulf-stream1.width-990_N5nBqXX.jpg"/>
<figcaption>The Gulf Stream is part of the Atlantic Meridional Overturning Circulation (AMOC), an Atlantic section of a global conveyor belt that drives surface and deepwater currents in every ocean, and influences the rate of sea ice formation at the poles. Image Credit: NOAA/JPL-Caltech
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Scientists hypothesize that such a shutdown may have occurred during the Younger Dryas. <a href="https://www.nature.com/articles/s41561-018-0169-6.epdf?sharing_token=F3sE8Eo9hOHZnYqD8YK7k9RgN0jAjWel9jnR3ZoTv0OX_eD6yrmH_7KKq-gygRSNxvqRGZfDf7DCL5eW-PfuvVeVS5aEtCzL4lRS0KXrvYe-24aRLXrqpLY9PKRR8pszYvChNUjQnC8PJGBB1IRUSURV1kNkXSchj5kFHdhB2udPaj7ghC_XFTmg7ke-eDC0SR1noiA_3Pf0AsrIuHsXUylW309RZffhMecEiWRknbQ%3D&amp;tracking_referrer=www.washingtonpost.com">As one theory goes</a>, as the planet warmed, glacial flood waters leaked into the Arctic and the North Atlantic, diluting the oceans’ saltiness, and weakening the AMOC. In addition, a massive ice sheet covering millions of miles—which helped contain an enormous glacial lake in what is now Canada—began to melt away. This triggered a freshwater flood, which traveled north up a river system and eventually emptied into the Arctic Ocean. This influx of fresh water ultimately decreased the salinity, and thus the density, of surface water in the northern Atlantic ocean to the point that it was no longer able to sink and make the return journey to the equator. So the AMOC shut down.Now, tens of thousands of years later,<a href="https://www.nature.com/articles/s41561-021-00699-z.epdf?sharing_token=fgt0vYw1E23vIb6z6zAzZNRgN0jAjWel9jnR3ZoTv0P93m6r2g6HCxEqjXwwP2zvNWm69miAlh1y_Z4SKXkP2NztMnWE6tMualAxgMFqr5BAxjwOlHhoLMeFCf0O_s1NN4HEUMLu7yNL5SvtNwdq4Qx78MVJ8W2EkmbQUfVnhfJ3ffV3HAA-WJn4cwtKnjyJnt5Q0NGn8v5HxLTpQFtiy9ur5aXEQwixPOLHKZ1qtGM%3D&amp;tracking_referrer=www.washingtonpost.com"> scientists have cautioned</a> that the AMOC is at its weakest point in over a millennium. But researchers have not been able to pinpoint how close the AMOC is to a total shutdown. Boer’s findings suggest a new insight: The AMOC’s decline may be indicative of an “almost complete loss of stability.”The new study’s primary findings are based on eight independent sea-surface temperature and salinity datasets spanning 150 years. Climate change is destabilizing the AMOC, Boers concludes, noting that the “restoring forces” that keep the AMOC functioning, such as temperature and salinity, have become more erratic.The stabilizing force of the AMOC is cold, salt-rich water, which sinks to the ocean floor and powers the circulation that keeps the AMOC in its “on” mode. Meanwhile, warming surface waters and fresh water from melting ice push the AMOC away from stability.Boers analyzed how fast the sea surface temperature was returning to its state of equilibrium and how big the deviations from this state were becoming. Boer’s results indicate that the strength of the stabilizing current is declining and that an AMOC tipping point—an ecological point of no return that once crossed could take hundreds of years to stabilize—is much closer than previously understood.“The signs of destabilization being visible already is something that I wouldn’t have expected and that I find scary,” Boers told <a href="https://www.theguardian.com/environment/2021/aug/05/climate-crisis-scientists-spot-warning-signs-of-gulf-stream-collapse">The Guardian</a>. “It’s something you just can’t [allow to] happen.”But a result of this magnitude needs to be tested by other researchers before it is widely accepted, Foukal says.
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As carbon dioxide accumulates in Earth’s atmosphere, the atmosphere and ocean trap more heat. As global temperatures rise, they trigger more glacial ice to melt. An influx of freshwater into the North Atlantic from the Greenland ice sheet will reduce the North Atlantic’s salinity and density, making the water lighter and less able to sink. In addition, warmer temperatures cause water molecules to spread farther apart, making the ocean waters even less dense. Similar to what happened during the Younger Dryas, if the water in the North Atlantic is not heavy enough to sink, the entire AMOC will shut down, Boers explains.In its 2019 “<a href="https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/">Special Report on the Ocean and Cryosphere in a Changing Climate</a>,” the United Nations Intergovernmental Panel on Climate Change (IPCC) stated that the AMOC is “very likely” to weaken due to climate change. But a total shutdown within the next 300 years, the report states, is only likely under a worst-case carbon dioxide emissions scenario with global average temperatures rising by 4.3 degrees Celsius by the end of the century.Still, Boers’ findings suggest that “the critical threshold is most likely much closer than we would have expected,” he says.<h3>The implications of a weakening AMOC</h3>Should the<a href="https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/"> AMOC weaken substantially</a>, it could “drastically” affect rainfall patterns in tropical monsoon systems, Boers told NOVA.Monsoons supply water to many parts of the world. Yackar Mauzole, an oceanographer whose research focuses on the Indian Ocean, points out that if the amount of precipitation and location of monsoon systems were to change, it would have major implications for the Maldives, India, Thailand, and other populous countries that rely on monsoons for agriculture.Weakening of the AMOC could also bring less summer rainfall to South Asia and the <a href="https://theconversation.com/sahel-region-africa-72569">Sahel</a>, the semiarid African region stretching from Senegal to Sudan that receives much of its rainfall from the West African monsoon, the <a href="https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/">IPCC projects</a>.“A change in monsoon systems would have severe consequences for the populations living in these regions,” Mauzole says. “Beyond oceanography and climate science, food insecurity should be something to consider if the AMOC were to transition in the future.”
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<img alt="The Maldives is on the front lines of climate change" class="richtext-image full-width" src="https://staging.pbs.org/wgbh/nova/media/images/AMOC_Body_Image.width-990_wuvtGuk.jpg"/>
<figcaption>A man operates a pump to try and clear flooded drains during torrential rain in December 2019 in the Maldives, the world's lowest-lying country. Image Credit: Carl Court/Getty Images
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To better assess what may happen in the future, some scientists are looking to the past. The AMOC shutdown 13,000 years ago led to an abrupt cooling of North America and Europe that lasted 1,000 years, they believe.<a href="https://www.pnas.org/content/109/13/4730"> Archaeological analyses</a> of skeletal remains and plant fossils from modern-day Syria and the Nile Valley suggest that the climatic shock of the Younger Dryas upended early human settlements, causing conflict, starvation, drought, and malnutrition, and led to the collapse of several agricultural civilizations.Today, as climate change <a href="https://www.carbonbrief.org/guest-post-could-the-atlantic-overturning-circulation-shut-down">destabilizes the delicate balance</a> of temperature and salinity the AMOC relies on, some scientists worry that the AMOC is already showing symptoms of decline. “It’s as though the AMOC is a patient newly arrived in the emergency room, and Boers has provided scientists with an assessment of its vital signs,” Woods Hole Oceanographic Institution President Peter de Menocal told <a href="https://www.washingtonpost.com/climate-environment/2021/08/05/change-ocean-collapse-atlantic-meridional/">The Washington Post</a> in August. “All the signs are consistent with the patient having a real mortal problem.”But the size and complexity of the AMOC system offer some hope: It will take time, close monitoring, and meticulous data collection before researchers are able to confirm an AMOC slowdown through direct observations, Foukal notes. Many realize the risk of waiting for evidence of a collapse.“The possibility that the AMOC tipping point is close should motivate us to try to stop it from happening. If we surpass a tipping point it could affect us for hundreds of years,” says Levke Caesar, a climate physicist at Maynooth University in Ireland who was not involved in the study. Research by Caesar <a href="https://www.nature.com/articles/s41561-021-00699-z.epdf?sharing_token=fgt0vYw1E23vIb6z6zAzZNRgN0jAjWel9jnR3ZoTv0P93m6r2g6HCxEqjXwwP2zvNWm69miAlh1y_Z4SKXkP2NztMnWE6tMualAxgMFqr5BAxjwOlHhoLMeFCf0O_s1NN4HEUMLu7yNL5SvtNwdq4Qx78MVJ8W2EkmbQUfVnhfJ3ffV3HAA-WJn4cwtKnjyJnt5Q0NGn8v5HxLTpQFtiy9ur5aXEQwixPOLHKZ1qtGM%3D&amp;tracking_referrer=www.washingtonpost.com">conducted in 2021</a> shows the AMOC is at its weakest point in over 1,000 years.Climate scientists are still unsure what threshold of carbon dioxide in the atmosphere would cause the AMOC to shut down. “The only thing to do is keep emissions as low as possible,” Boers told The Guardian. “The likelihood of this extremely high-impact event happening increases with every gram of CO2 that we put into the atmosphere.”
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New evidence suggests that the larger system the Gulf Stream is part of is approaching a tipping point that could cause dramatic shifts in global weather patterns.

Portable Homes Help Communities Adapt to Climate Change

See how one Alaskan community is dealing with the effects of rising Arctic temperatures.
As Alaska&#x27;s permafrost thaws, Indigenous communities are looking for housing solutions, including building homes on steel sleds.
Portable Homes Help Communities Adapt to Climate Change Published: February 8, 2022NARRATOR: In the roads outside Utqiagvik, the effects of rising Arctic temperatures are easy to see.LARS NELSON: Just from observation, growing up here, coming out here, since I was a kid, the roads were a lot higher than they are now. It is literally sinking.His bumper might get wet.NARRATOR: Native Alaskan Inupiaq Lars Nelson is an infrastructure consultant. He knows first-hand what permafrost thaw is doing to his community.LARS NELSON: This road is for subsistence use. We come out here and stage our hunts. It’s a big part of our history. And it’s important that we’re able to access it, in case of an emergency.NARRATOR: And it’s not just the roads that are sinking. In downtown Utqiagvik, Nelson meets Inupiaq Anthony Edwardsen.ANTHONY EDWARDSEN: These ones are subsiding, too.NARRATOR: He’s an expert on the Inupiaq community, with four decades experience in the construction industry.LARS NELSON: This one is really messed up. Look how it’s just...ANTHONY EDWARDSEN: That’s where the houses are sinking.NARRATOR: Local houses are built on wooden pilings. If they were built on the ground, the heat used to warm the homes would thaw the permafrost below. But now, the permafrost is thawing by itself, and the pilings are starting to sink.ANTHONY EDWARDSEN: When the piling is a very small base, it doesn’t hold its structure.LARS NELSON: The communities, they need the house levelling, move houses, houses need to be torn down. We’re in the middle of a housing crisis.NARRATOR: Nelson believes strategic building is the answer.LARS NELSON: We’re on to it, right now, and we’re refining it, right now. We can build nice, good, healthy homes. We just got to pay attention to our foundation, pay attention to the tundra we’re building on, more closely, because it’s such an awesome spot, you know? It’s the top of the world.NARRATOR: But as the permafrost continues to thaw, others in Alaska are looking at more drastic solutions.GRIFFIN HAGLE (Taġiuġmiullu Nunamiullu Housing Authority): So, this is our portable, adjustable, sled-base home. It is on a giant steel sled, as opposed to the pilings.NARRATOR: C.E.O. of the regional housing authority, Griffin Hagle has a more radical plan for sinking homes.GRIFFIN HAGLE: What we would do if we needed to, to move this, we would be hooking up our tow chains to these two attachment points. We’ve got one on this side and one on that corner of the building over there. Hook that up to a piece of heavy equipment, Caterpillar®, and then drop it off the pads and, basically, tow it across the snow, in the wintertime.NARRATOR: As temperatures rise, Hagle is searching for ways to protect some of the most isolated communities in the United States.GRIFFIN HAGLE: This is the largest municipality in the world, I think, by land area. We provide affordable housing in eight villages, across an area the size of Minnesota, only without any roads.NARRATOR: No Alaskan homes have been sledded away, yet, but Arctic warming has forced some towns to relocate. And Hagle thinks houses will soon be on the move.GRIFFIN HAGLE: And there’s several communities, especially in rural Alaska, native communities, that are increasingly at risk of relocation due to global warming. And so, this gives us an advantage in having the option, the adaptability, to move that that structure if it becomes necessary.Native people, the indigenous communities that have called this place home for thousands of years, have come up with all sorts of innovations to make life work here. So, we draw a lot of inspiration from that, and we see that as kind of the continuation of a long tradition of innovation.

See how one Alaskan community is dealing with the effects of rising Arctic temperatures.

Topic: Planet Earth

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