The Last Time the Globe Warmed

Thanks to Curiosity Stream for supporting
PBS Digital Studios. Imagine an enormous rainforest teeming with
life: trees, insects, pretty little birds. Primates are climbing in the canopy, while
crocodiles and turtles swim in the rivers below. Beautiful, isn’t it? Now imagine this lush rainforest … in the
Arctic. There was a time — and not too long ago — when
the world warmed more than any human has ever seen. So far. This ancient warming took place over the course
of just 200,000 years — the blink of an eye in geologic time — and it ended much like
it began: suddenly and mysteriously. It all started 56 million years ago, at the
very end of the Paleocene Epoch. Back then, life was still recovering from
the unpleasantness of the Cretaceous-Paleogene extinction event, which wiped out the non-avian
dinosaurs. And things were already warm by today’s
standards. There were no polar ice caps, which meant
sea levels were much higher. And the continents — which were just beginning
to take a familiar shape — were covered in habitats like temperate forests, and deserts,
and a belt of rainforests around the equator. But this environment was about to change. In fewer than 20 thousand years, the global
average temperature increased by 5 to 8 degrees Celsius. And the warming was greatest at higher latitudes. So, at the poles, temps on land reached an
average of 23 degrees, while the ocean waters got up to a balmy 20 degrees, This means you
could’ve gone for a comfy swim in the seas around Antarctica! This remarkable and sudden warming event is
known as the Paleocene-Eocene Thermal Maximum, or PETM, and it had a massive effect on
life on Earth. For one thing, when the PETM reached its peak,
rainforests had expanded much farther than they ever had before. Fossils from North America, Europe, and Asia
reveal habitats rich in plant life that today are associated with tropical rainforests
— even though these forests were nowhere near the tropics. The fossilized fronds of palm trees have been
found as far north as Wyoming, for example. And some places within the Arctic Circle,
like Ellesmere Island in Canada, show evidence of ferns, redwoods, and gingkos. So. How was all of this — any of this — possible? Our best clues can be found in ancient sediments. Marine sediment samples from Maryland to Antarctica
show that, about 56 million years ago, there was a sudden spike in the amount of carbon
dioxide and other greenhouse gases in the oceans. And judging by the types of carbon found in
these sediments, the gases likely came from organic matter, like plants. See, plants, like most living things, prefer
to use the lighter and more common isotope of carbon, carbon-12, as opposed to heavier
isotopes, like carbon-13. So, this biogenic carbon — which we’ve
talked about before — has a different chemical signature than carbon that’s never been
part of a living organism. And, sediments that date to the start of the
PETM, show a large and sudden drop in the ratio of carbon-13, compared to carbon-12. This means that a bunch of biogenic carbon
must have suddenly been released into the atmosphere, in the form of carbon dioxide,
methane, and other gases. But, where did these gases come from? Well, one hypothesis is that there was a rash
of massive wildfires that unleashed tons of CO2 that had been locked up in plants. Another model proposes that giant seams of
coal were exposed to the heat of volcanic activity, which would have released the carbon
from fossilized plants. Or it could be that an otherwise mild warming
event triggered the release of greenhouse gases, by melting deposits of a compound known
as methane hydrate. Methane hydrate is similar to ice, but it
contains molecules of methane trapped by molecules of water. And hydrates are usually stable, as long as
they’re under a lot of pressure, like deep in the oceans, or if they’re kept cold,
like in permafrost — the thick layer of frozen soil that forms in cold climates. But if these places warm up, the hydrates
melt, releasing bursts of methane, which is an even more potent greenhouse gas than CO2. And of course, the more warming that happens,
the more melting there is, which releases even more greenhouses gases, creating a classic
positive feedback loop. Now, no matter how it started, it’s worth
noting that, during the PETM, carbon was released into the atmosphere at only a fraction of
the rate at which it’s being emitted today. One study of marine sediments from the Arctic
showed that, at the peak of the PETM, as much as 1.7 billion metric tons of carbon were
released into the atmosphere every year, for at least 4,000 years. A similar study of sediments from New Jersey
put the figure at about 1.1 billion tons of carbon every year. Now, compare that to the amount of carbon
being released today. In 2014 alone, it was 9.8 billion metric tons
of carbon. So, 56 million years ago, carbon was being
released less quickly than it is now, but those emissions continued for thousands of
years. And it was more than enough to create a potent
greenhouse effect. With more carbon in the atmosphere than plants
could absorb, the planet started to change rapidly. In many places, the climate delivered a combination
of humidity and heat that allowed vast rainforests to flourish. And among the animals that thrived in these
warm forests were reptiles. Fossils of alligators, crocodiles, and turtles
can be found in nearly every fossil bed from the PETM — even in the polar forests of Canada
and Greenland. And these lush forests were also where many
early mammal groups diversified — including our every own lineage, the primates. In fact, the earliest true primates appear
in the fossil record just as the PETM was starting to take off, 56 million years ago. They adapted quickly to a world covered in trees, developing things like forward-facing eyes, fingernails instead of claws, and opposable
thumbs. These features gave primates such an edge,
that by 53 million years ago, they could be found across the northern hemisphere — from
tiny Eosimias in China to Notharctus in Wyoming. But in the oceans, life in hothouse Earth
became much harder. In fact, in some places it was almost impossible. At the equator, ocean temperatures were unbearably
hot, sometimes reaching as high as 36 degrees, almost as hot as your average hot tub. This was probably too hot for many kinds of
plankton, which were — and are — the basis for most ocean food webs. But an even more devastating side effect of
high CO2 levels was ocean acidification. When ocean water absorbs CO2, it becomes more
acidic. And this in turn depletes the water’s concentration
of carbonates — the compounds that many organisms use to build shells and other structures. And this is why one of the clearest effects
of the thermal maximum can still be found in core samples from the deep sea. Sediments that date back to before the warming
are typically pale in color, because they’re rich with the skeletons of deep sea foraminifera. Also known as forams, these are tiny protozoans
that build shells of calcium carbonate. And where forams were abundant, the chalky
fossils of their shells turned the ocean bed white. But when the oceans became more acidic, the
sediments turned dark. Because … most of the forams just disappeared. During the PETM, between 30 and 50 percent
of all foram species went extinct. The same phenomenon also stunted the growth
of hard corals, which need carbonates to build their skeletons, too. So, during the PETM and for millions of years
afterward, big, complex coral reefs all but disappeared from the fossil record. All told, the thermal maximum was a mixed bag
for life on Earth – proving to be an important period for us mammals, but a major loss for
some marine life. And, like all dramatic events, the PETM did
come to an end. Although, we’re not sure how, or
why. Over the course of the Eocene epoch, the climate
slowly began to cool. And although the temperature occasionally
spiked again, it never reached the extremes of the maximum. Temperatures kept dropping during the Eocene
— so much so, in fact, that by the end of the epoch, 34 million years ago, polar ice
caps had begun to form. But, how did we get from rainforests near
the poles to ice caps? Well, the cause of the initial cooling that
actually stopped the PETM 53 million years ago remains a mystery. But something allowed that cooling to take
hold, and make the world even colder. And the answer here might have to do, again,
with plants. Arctic sediments that date back to the early Eocene
— 49 million years ago — have been found to contain huge swaths of fossilized aquatic
ferns known as Azolla. These plants thrived in the lush, warm Arctic. But as the environment changed, they died
off. And as they dropped to the seafloor, the thinking
goes, they took tons of carbon with them, which caused temperatures to drop even further. Despite how little we know about its end,
or its beginning, the Paleocene-Eocene Thermal Maximum shows us just how polarizing climate
change can be for life on Earth. For some organisms, like early primates, the
warming was a chance to develop new forms and spread to new locations. But for corals, forams, and other marine life,
such extreme heat spelled disaster. It gives us, in the midst of our own period
of warming, a view of how extreme the effects of climate change can be. And it allows us to make some pretty striking
comparisons. Remember when I said that, during the PETM,
the globe warmed more than humans had seen so far? Well, keep in mind that, in recent years,
the rate of annual carbon emissions have been more than five times greater than they were
at the peak of the PETM. As a result, our world is warming faster
than it did back in the Eocene. Just over the past hundred years, the average
global temperature has increased by about 0.7 degrees Celsius. But that’s just been over the past century. During the PETM, it took perhaps thousands
of years for temperatures to rise that much. So the PETM is the closest we can get to understanding
the effects of global warming today. And it has a lot to teach us about the extremes
that life experienced, on land and in the seas. Yes, rainforests full of primates and insects
and reptiles is beautiful. But I think you’ll agree with me that most
of us like them right where they are today. PBS Digital Studios is sponsored by Curiosity
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Comments 100

  • You mean the Earth can just spontaneously warm up without obvious reason? Who knew?

  • Great! I like warm water swimming and a nice tropical backyard with lots of tropical fruit to eat. Might need a "swamp" cooler….for washington

  • This might be our future

  • If the ocean temperatures drop to 36°, I'm staying on the beach. This time of year Gulf of Mexico runs 82°which is fine by me.

  • 56 million years ago we have scientific PROOF that dinosaurs invented the combustion engine and spiked CO2 levels worldwide.

  • C12, C13 and C14 are chemically identical.

  • I find it rather interesting that carbon dioxide made the ocean more acidic when baking soda moves things more base. I'd love to know how that works. It seems like a rather large gap in the logic.

  • My Dad: This happens all the time, the temperature was just like this when I was younger.


  • hahahahahahahahahahahahahahahahahahahahaha..lying clown

  • Møkka prat..

  • Screw this nerd, rainforests should cover the globe . . . Mwahahahaha

  • The entire story is based upon the premise that carbon release preceeds global warming, yet you specifically mentioned the release tens of millions of years ago occurred over a very long frame of time, implying CO2 levels rose concurrently with the rise in temperature, as would be expected due to increased plant life that subsequently fed fires and biological decay.

  • Ha ha! Did you not get the memo?!? Climate change is MAN MADE!

  • Climate change hmm watch this –

  • Termites produce more Co2 than humans, let that sink in. We make no difference

  • I support global warming!

  • When you buy land in the artic for future housing. Stonks!!

  • If humans are the cause of the planet warming then what caused it to warm then ?

  • So no one going to talk about the streams disappearing? This means many countries like uk will face very different weathers and the ocean life will drastically change…

  • We are so smart we are stupid.

  • Just for comparison 37C is body temperature.

  • Why is Iceland greener than Greenland, and how did the United states of Ireland end up so far west?

  • there is no scientific consensus that life is important.

  • So, an increase in atmospheric carbon could help agriculture flourish, and possibly end world hunger?!?

    Nah, I'll pass.

  • Glad to know the planet can get that warm and we’ll be just fine! Let me go rev my diesel up.

  • I feel so smart watching this.

  • Paleocene. Paleogene is a MMA cage fighter.

  • Maybe THE SUN!

  • How did you come up with the figure for how much CO2 is being released into our atmosphere>?

  • The climate is always changing. When you believe it shouldn't change is a sign of arrogance.

  • There not talking about the helium being released into the atmosphere. The meltdown of the ice will cause the greatest pole shift ever seen. Right now we are living a proton electron proton environment. After the pole shift, we will be living in an electron proton electron environment. This environment will be a super electromagnetic spectrum. NASA and other governments know about this coming change and their not telling the world. They don't tell us anything anyway.

  • Total bollox

  • Thanks! Is it now common to say, "non-avian" rather than "lizard-hip"? Just wondering. 𝓡𝓲𝓴𝓴𝓲 𝓣𝓲𝓴𝓴𝓲.

  • So basically if there's global warming i can grow natural all year round in New England?…let me warm up my 82 Mercury Topaz….

  • The earth is cleaning itself

  • Plate techtonics, ocean composition, and tidal forces, all make EXTINCTION. THEY ALL MAKE WEATHER

  • No, I don't agree! I'd much prefer a world where temperate forests could become common inside the arctic circle

  • oh well, dont no why everyone bothers to worry about climate change anyway… we will all be gone way before the affects of our co2 emissions affects the planet dramatically 🖒

  • With human activity and technology being around, this tine i suspect things will be considerbly worse for other life forms and those who cannot afford to adapt or migrate…

  • In other words: Global warming expands life and Global cooling threatens life.

  • Well, 36 °C is an extreme temperature. … Damn! Growing up in southern Florida, I must have missed that bulletin. You know what reefs and Dinosaurs didn't have? Air Conditioning and Greenhouses. We do. We can also generate enough power to run it all. If the climate does run away, we can beat it. Once we reach that point, we need to flow with it. Here is what this video totally missed. The last time this happened, there were no humans with SUV's!!! That is the biggest problem. If it is just about science, there is no way to justify taxing everything and ensuring that only the rich can afford more than a minimum existence as a cog in the machine. The solution to every problem is taxes and regulations. Because making the populous bend over and squeal like a pig emits less CO2 than a lawn mower. This is where the green people went inbred stupid. If they had just stuck with science instead of latching it to a socialist agenda, plan B would already be in effect and plan C ready to go.

  • What about Milankovitch sun cycle,
    Milankovitch Cycle – Universe Today A Milankovitch cycle is a cyclical movement related to the Earth's orbit around the Sun. There are three of them: eccentricity, axial tilt, and precession.
    Variaciones orbitales,
    Milankovitch cycles – Wikipedia

  • Ask a demonrat anti American Communist scum bag.. it's cow farts…MAGA🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸

  • 1:10 According to climate data collected in Antarctica the temperatures would had to have risen a lot higher than 5-8c to melt the Antarctic interior. If you Wikipedia Vostok, South Pole, Plateau Station, you will see all these places annual mean temperature is around -50c. Even their warmest months mean temperature is around -30c. In fact the "hottest"of these 3 stations is the South Pole, it's highest temperature ever is -12c. So even if inland Antarctica rose 20c it will still be a frozen solid block!!

  • That seems like an awful lot of carbon dioxide that we are emitting.
    To be honest if the carbon dioxide is only .04% of the atmosphere and humans are only responsible for 3% of carbon dioxide emissions then I really don’t see how we could make much of a dent in emissions of that scale!!
    Am I getting something wrong?
    Also for the past 30 years or so we have been complaining of humans cutting down the rainforests and rightly so in my opinion. Why then do we not sanction the countries doing it?
    If not sanctions, why not pay them not to do it.
    So many things don’t add up

  • Two estimates for CO2. Let’s use the smaller one for dramatic effect.

  • but how rainforest in arctic could cope with polar nights?

  • Need trees

  • Ask not what the planet can do for you, but what can you do for the planet.

  • I like how we can tell the weather millions of years ago but can’t get it right day by day

  • the last time the earth warmed was the last 12,000 years. now that short warming period is coming to an end. we are entering the eddy minimum now.

  • The last time the Earth warmed was because the continents were moving we know earthquakes can move the position of the Earth in space…and a lot of the other stuff was happening …but a lot of what was happening was do to the earthquakes to so …………….🤣😂

  • Past time to plant a massive amount of trees! Let's get busy!

  • its called global warming

  • Its over, get ready for chaos… I hope I can prepare to survive as long as I can

  • The Sun! Makes it warmer. Now the sun is cooling. It will get cooler. The solar minimum is ramping up.

  • it proves that time travel is invented in the future because we all know all global warming is manmade. So, evil corporations from the future invent time travel as a way to avoid paying carbon taxas. they time traveled the pollution into the past. DAMN…DAMN…DAMN THEM! KOOKOO KOOKOO KOOKOO

  • Time to put a pollution tax on china!!!

  • Why? If not the global warming there would be no evolution of primates… so..? What if we will be able to live in Antarctic..? From what other say the carbon dioxide was not 300ppm but around 2500ppm.. (problem is that with burning carbon we use oxygen.) Another thing is that some scientist say that actually we need that co2 because without it plants will die of hunger. What if they would use all the co2 from the atmosphere? All the life would extinct. What about solar activity? Not mentioned.

  • The catalyst for these events is very simple.
    Chuck Norris got chilly.

  • global warming is a great gift to unleash all the tundra and ice and revert to nice forests and more animals not just a few polar bears. We need to hurry it up so more houses can be built and people move up north.. Canada property worth little now is skyrocketing in value.

  • More heat in the atmosphere and more water being released from solid state = higher percentage of gaseous water in the upper atmospheres. Heat bounces off planet and planet cools "rapidly." Thanks water.

  • global Warming is evil!!! 😈

  • Most of the planets C02 is stored in the oceans. It can be released due to a seismic event. Also freshwater lakes store vast amounts of C02 waiting to be released. Google Lake Nyos where 1700 people died over night in 1986. Gives you an indication of just how much is stored. Man needs to clean up his act, that much is true, but he is just along for the ride when it comes to nature and the ever changing cycle of climate change.

  • How about telling the truth like in the spring

  • Were only along for the ride! Enjoy every day

  • It's really amazing the planet has redundant systems to regulate itself, and if any one species abuses it too much it's going to let you learn a hard lesson then clean itself up! I don't think massive carbon emissions is a lesson we want to be taught.

  • yes we are still in an iceage, but iceages only make up %25 of earths climate history, a more normal/average earth climate is co2 in the thousands and zero year round ice at the poles.

  • no i dont agree with you, i want to earth to live life to its maximum, and thats not in an iceage.

  • AOC can't stop coming solar minimum, no matter how much money you give her. She can't even combat all the racist cauliflower.

  • Uhh… Medieval Warming period anyone, just a couple centuries ago? There is still ice from the last 600 years yet to melt.

  • Ginko and Redwoods are not tropical plants.

  • This good infor from a more direct effect on the warming of the earth, But we must realize that we are constantly moving in space and since we just finished our 26,000 year trip around the Galaxy we will be experiencing unknown global changes which occurred to the earth 26K years ago and as you look at the arm we are in traveling around the galaxy you will see we will pass closer to other star systems and those star systems may be closer than they were the last trip around. so just sit back and enjoy the ride because there is nothing we can do to prevent the changes we are soon to see at no fault of our own because where this bus takes us is where we all will ride.

  • Yes they are called trees

  • This will be awesome, a whole new real estate market in the Arctic. Lol they said we had no more room for people.

  • I think I like the warmer earth better. Going out to the garage now to start all three cars and let them run all night. Gotta get this planet warmed up.

  • (36°C × 9/5) + 32 = 96.8°F

  • The is no greenhouse effect

  • Hey PBS, could you guys do a video about the medieval warming period? Relevant to today's discussion re Co2 and global warming/climate change, don't you think?

  • Here's a shout out to all of you ignorant sceptics: CLIMATE CHANGE IS REAL!!! Need proof? Look here – even Reykjaviks past temperatures are changing. Source: NASA

  • I say it was Humans

  • Enlighten. And it makes me wonder if we are beyond the point of no return. Is it possible to answer that question

  • The way to explain the artic being warm is the earth shifted on its axis , it has happened before , a 90* shift has been proven.

  • An axial tilt has happened in the past and will happen again.

  • We're still close to iceage and we still have a long way to go

  • La tierra se renova cada que ellos quieran es como tocdo tiempo

  • Did the continents not move ?

  • As an evolutionary biologist, I love these presentations. However, pleeeeeease slooooow down! I get tired trying to keep up with the speed at which you talk!

  • Carbon is not the control knob of climate. Poor presuppositions

  • Just more guessing, we are starting into a cooling period that will give the fanatics something new to obsess about .so many intelligent stupid people.

  • What about the last 7 Ice Ages ???? thats at least 8 Times the world has frozen and thawed , it's all cyclical . Climate Alarm is Communism in disguise .

  • Imagine how much tax this could have raised…

  • since the 70s we have been putting more and more water in sealed containers….it can be anything from simple bottled water to dish soaps sports drinks, soups, closed chillers units, antifreeze…the list is very large and goes on

    water is made up of two hydrogen atoms and one oxygen atom….which makes it a molecule …one molecule is what we call vapor….it is only when a bunch of those molecules start clinging together that it is liquid
    the reason this is important is because H2O doesnt act like you think it does…because as it evaporates and becomes a vapor those molecules separate again

    now then…to the climate part
    every cooling system has a certain amount of coolant that is need to keep it at optimum temperature…earth is no different
    for instance take 2 pots of water…one 1/4 full and one all full…..heat them up at the same temperature…..the one that is 1/4 full heats up faster makes steam (humidity) faster

    same for the earth …since all this water is being put in stored containers …it is not circulated …..less H2O molecules in the air….they cant combine to make liquid that can circulate

    right now there are the same amount of H2O molecules on earth as there were in the beginning, so no, those molecules are not gone…they havent went into space….the reason they are gone is because we put them in sealed containers

    so if we deal with the water shortages ….water in sealed containers……then we can deal with the climate heating up

    or we can just wait till some of the ice is melted….yup

    because H2O as a solid doesnt circulate or evaporate till it is melted….once it is melted a little…the ground water and the heat index temps will be back to normal

    as I said…this is unrefined, I wrote it in a hurry to reply to a USA TODAY video on water disappearing

    I have this idea in my head and cant get it out in a coherent way for most people to understand…yes it goes way out there, but it is something that no one else is addressing , the water levels around the globe have decreased…..look at california, all the reservoirs…..michigan residents have stated that nestle has made their ground water drop in their rivers and streams…..there are documentaries on this

    I wish someone would actually look at this because I'm certain this is a big deal

    but as I said…we can just wait for the polar caps to melt and replenish the H2O molecules that are able to circulate
    remember…H2O is just a molecule until it combines with another H2O molecule…then it becomes a gas, then a mist, then moisture, then water…..ask yourself…how many H2O molecules in a visible water drop…the answer is
    there are 1.67 sextillion water molecules in a water drop…fact

  • Sounds like we lived here before

  • So, don't you see? All this mad rush to warming up the earth again was because there was a meeting one night of some folks that were down right tired of trying to figure this one out. And so they invented the internal combustion engine, electric power plants that burn coal ect..

    Darn those pesky know it all's…. They will go to any ends if they have a question bugging them and keeps them up at night..

  • If I had to guess, I would say the earth shifted on its axis causing the seasons to disappear and the equator to remain the closest part of the planet to the sun, thus warming the ocean and currents feeding the polar regions…this would leave no trace on earth other than the climate changes outlined in the video…unfortunately that doesn't "fit the narrative" so science will claim it's a mystery. I really get tired of so called scientists downplaying the Milankovitch cycles and solar cycle in favor of greenhouse gases, which actually follow temperature increases, not preceding them. There is nothing else that can explain the regularity of glaciation…just saying.

  • Sounds awesome, life flourished!! Bring on the warming!

  • Plants "prefer" to use the Carbon-12 (C-12) isotope (2:30)? Isn't the C-12 isotope more common in plants, because C-12 is more common in the atmosphere?

  • Now these big companies have made billions from destroying the planet and the governments have their taxes; it's all OUR fault…. Fu*k right of*!

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