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Has Earth’s climate ever changed as fast as it is today?

The speed of today’s global warming stands out in our reconstructions of Earth’s history. And we can say with confidence that human society as we know it has never experienced such fast and sustained worldwide warming.

 

May 18, 2026

Humans are heating up the planet, and we’re doing it fast. As we pump out climate-warming pollution—most importantly, carbon dioxide (CO2)—global temperature is rising. Our thermometers make that clear: For instance, 2015 through 2025 were the warmest eleven years in the over 150-year-long record of observations.1

But what if we want to look deeper into the past, before those thermometers were around? Enter paleoclimatologists, who uncover ancient clues to piece together a longer planetary record. By studying past episodes of climate change, we can learn more about what to expect as the world warms now. So it makes sense to ask: Can we point to another period in our planet’s history when the world warmed as fast as it’s doing today?  

“I think the short answer is, to the best of our knowledge, no,” says Vince Cooper, a postdoctoral fellow at MIT who studies paleoclimate. “At least, it doesn’t show up in the data we have available.”

That’s important, because as humans and other species cope with a changing climate, how much the world shifts around us isn’t the only thing that matters; how fast we get there is crucial, too. A rapid uptick in temperature is much harder to adapt to than slow, steady warming.

There’s a wrinkle, though: Gauging the pace of past climate change is trickier than you might expect. We often think about warming today roughly in terms of changes from decade to decade; this is a timescale that’s relevant to humans and the ecosystems around us. The trouble is, “the past gets blurrier the farther we look back,” Cooper says. “As soon as we go beyond the instrumental era, we have to start looking at records that have increasingly less fine resolution.”

For the more recent past (geologically speaking), scientists can use high-resolution record-keepers, like tree rings and corals, that mark out changes from year to year. But to look farther back, they have to rely on other time capsules—and the picture starts to get fuzzier. For instance, the stacked layers in ice cores can preserve information about the climate stretching back hundreds of thousands of years. But while you can pick out annual layers in more recently-formed ice, older, deeper layers are squished too thin to distinguish.

“You’re left only being able to conclude that these data points that you measure in the lab represent longer timescales,” says Cooper. In very old records, “it’s impossible, with current methods, at least, to identify things like decadal rates of warming.”

Consider the rhythm of ice ages over roughly the last million years, which have ebbed and flowed in 100,000-year cycles. Archives like ocean sediments and the deep parts of ice cores help reveal this regular pattern, with the Earth warming or cooling several degrees Celsius over many millennia. But in these coarser records, ups and downs that occur from decade to decade—superimposed on those longer, slower trends—get smoothed over. This means if the world had experienced a pulse of much faster warming, as long as it was short-lived enough, it wouldn’t be measurable in these records.

“We can never completely deny the possibility that some rapid warming happened in the past,” says Cooper. “But we can look back and say we don’t see something like today.”

For the more recent past—in particular, the age of human civilization—we have more and higher-resolution records, and are especially confident that past episodes of climate change were slower than today’s.

For example, scientists have combined temperature data from sources including trees, corals, and lake sediments to reconstruct global temperature over the last two millennia.2 This and other work led the Intergovernmental Panel on Climate Change to conclude in 2021 that the Earth had warmed faster during the previous half-century than during any other 50-year period in at least the last 2,000 years.3

Another study zoomed farther out, combining hundreds of records from ocean sediments with a computer model of the Earth to track temperatures over the last 24,000 years, deep into the last ice age. This method, bolstered by a wealth of records from around the world, shows that the rate of warming we’ve seen over the last century stands in stark contrast to changes in the past.4 (For perspective, 24,000 years ago, the rise of agriculture was still many millennia away.)

So the warming humans are causing today stands out against the climate we’ve experienced since we’ve had farms or cities—let alone cars or electricity.

What about much farther in the past? Our temperature records grow increasingly fuzzy, but Cooper says there’s another way of tackling this question. If there have been periods of warming as fast as today’s, we might be able to find them by asking what natural processes could cause them.

Cooper points out that our rapid release of climate-warming pollution is very different from, say, the shifts in Earth’s orbit that have brought the planet in and out of ice ages; those changes are big overall, but they unfold over “many thousands of years, and very consistently and slowly.” We do know, however, that Earth has also seen massive natural releases of CO2. “We can go back in time and say, what could possibly release a lot of CO2 into the atmosphere, and how fast could that happen?” says Cooper.

For one of the best candidates, he says, we can travel back 56 million years to the “Paleocene-Eocene Thermal Maximum,” when global temperature spiked. Natural processes—volcanoes are a likely culprit5—pumped out CO2, and its concentration in the atmosphere rose sharply. Still, Cooper says, scientists estimate that the rate of CO2 accumulation during this period was several times slower than what humanity is doing today.6

He notes that, if you zoom in, you can find periods of very fast warming in specific regions of the world. For instance, the last ice age was punctuated by very abrupt “Dansgaard-Oeschger events,” spikes of extreme warming in the North Atlantic region that unfolded in a matter of decades.7 But Cooper says, while the effects could be felt far and wide, this warming didn’t span the world as we’re seeing today. The truly global scale of today’s rapid warming is part of why it’s so distinctive.8

Paleoclimatology can help us learn about how the Earth system works, and ancient changes in climate could provide clues to what we might expect in a warmer future. “But none of them are a perfect analogy,” Cooper says. “So when we think about the changes today, we have to own up to the fact that this is a new phenomenon that we are causing by adding so much CO2 so rapidly.”

 

Thank you to Ramón Vázquez of Valladolid, Spain, for the question.

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Footnotes

1 World Meteorological Organization (WMO). State of the Global Climate 2025 (WMO-No. 1342). 2026. https://doi.org/10.59327/WMO/S/CRI/SOC1.

2 See, e.g., PAGES 2k Consortium. "Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era." Nature Geoscience 12 (2019). https://doi.org/10.1038/s41561-019-0400-0.

3 Gulev, Sergey K., et al. "Changing state of the climate system." (2021). In Masson-Delmotte, Valérie, et al (Eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 287-422). https://doi.org/10.1017/9781009157896.004.

4 Osman, Matthew B., et al. "Globally resolved surface temperatures since the Last Glacial Maximum." Nature 599 (2021). https://doi.org/10.1038/s41586-021-03984-4.

5 Haynes, Laura L., and Bärbel Hönisch. "The seawater carbon inventory at the Paleocene-Eocene Thermal Maximum." PNAS 117 (2020). https://doi.org/10.1073/pnas.2003197117.

6 Li, Mingsong et al. "Astrochronology of the Paleocene-Eocene Thermal Maximum on the Atlantic Coastal Plain." Nature Communications 13 (2022). https://doi.org/10.1038/s41467-022-33390-x; Tierney, Jessica E., et al. "Past climates inform our future." Science 370 (2020). https://doi.org/10.1126/science.aay3701.

7 Jansen, Eystein, et al. "Past perspectives on the present era of abrupt Arctic climate change." Nature Climate Change 10 (2020). https://doi.org/10.1038/s41558-020-0860-7.

8 Berger, Sophie, et al. "Frequently asked questions (Chapter 2)." (2021). In Masson-Delmotte, Valérie, et al (Eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 287-422). https://doi.org/10.1017/9781009157896.004; Neukom, Raphael, et al. "No evidence for globally coherent warm and cold periods over the preindustrial Common Era." Nature 571 (2019). https://doi.org/10.1038/s41586-019-1401-2.

Madison Goldberg
by Madison Goldberg, MIT Climate Portal Writing Team
Vince Cooper
featuring guest expert Vince Cooper, Houghton Postdoctoral Fellow, MIT Department of Earth, Atmospheric, and Planetary Sciences
Related MIT Groups
More Resources for Learning
MIT Climate Portal: "When scientists reconstruct ancient climates from ice cores, how do they create an accurate timeline?"
MIT Climate Portal: "How do we know what the Earth's climate was like millions of years ago?"
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Carbon Brief: "Mapped: How 'proxy' data reveals the climate of the Earth's distant past"
xkcd: "A timeline of Earth's average temperature"
Jessica E. Tierney et al., Science: "Past climates inform our future" (Scientific Article)
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Want to learn more?

Listen to this episode of Ask MIT Climate on Earth's climate history.

LHF: Hello, I’m Laur Hesse Fisher, and you’re listening to Today I Learned: Climate from the Massachusetts Institute of Technology.

Imagine, for a moment, that you’re standing on a massive sheet of ice that spans from the high Arctic, all the way into the northern United States. At its thickest point you could drill down through almost two miles of solid ice before reaching land. 

Today on our episode, we are going back in time to visit past versions of our Earth that are wildly different from today’s. 

And why? Well, because the Earth’s climate has changed before—many times before!—and folks like you have written in and asked us about it. What caused the Earth’s climate to change in the past? And what can it tell us about the climate change that we’re experiencing today?

Fortunately, we know someone at MIT who knows a lot about the history of the Earth’s climate.

DM: My name's David McGee, and I'm a professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT. And I study paleoclimate, which is the study of the natural history of Earth's climate.

LHF: It turns out that our planet has changed a lot before we humans came onto the scene. There was a time, for instance, when the whole center of North America was engulfed by an inland sea, a time when alligators crawled in the Arctic, and forests flourished near the south pole. 

And that’s because the Earth has gone through some wild changes in temperature.

DM: Even in the last 1% of Earth history, so last like 45 million years, we've seen changes in the Earth's mean temperature of roughly 30 to 40 degrees Fahrenheit. So huge changes in the mean global temperature.

LHF: But how do we know about these big changes in temperature? Well that, really, is the story of paleoclimate, and it begins in earnest in the 1700s, with some peculiar rocks.

DM: People had noticed boulders that didn't match the local bedrock, in places where it didn't really make sense that there should be boulders, in Scotland, Ireland, around eastern North America. They noticed striations or grooves in the bedrock. And they realized that these striations were things that were observed near modern glaciers. And so people started to piece together this story that there had been very large ice sheets in places where there weren't currently ice sheets.

LHF: In 1824, a geologist named Jens Esmark first proposed that these ice sheets were not just local, but a single vast mass of ice that once covered much of the Northern Hemisphere: in other words, that the world had undergone an ice age.

Over the next century, scientists would find more and more evidence proving his theory, eventually learning that, 20,000 years ago, a quarter of the Earth’s land surface was covered in ice, year round. And that raised a new question: just how cold was the Earth during this ice age? To answer that, scientists needed some extraordinary new tools.

DM: Paleoclimate is the art of the possible. You know, there's only so many things that you have that are left over from thousands of years ago, there's even fewer that are left over from millions of years ago, and even fewer from hundreds of millions of years ago.

So we have to rely upon natural archives, things that grow or are deposited and somehow record information about the climate around them as they form.

LHF: And these archives need to be preserved for a very long time. Scientists have only found a few of these relics of the deep past: often buried in unchanging environments, like Antarctic ice or sediments in the deep sea.

DM: And in both of these archives, you have deposits building up year after year after year. And if you're able to drill or core down into them, you essentially have a time machine.

I'll just give you an example. There is a certain type of plankton that lives in the surface ocean. These are called foraminifera, and they're about the size of a grain of sand. Really small. They happen to form small calcium carbonate shells. So just like a clam might, but they're so small that they're able to float around in the surface ocean.

LHF: And when the foraminifera die, their shells fall to the ocean floor and are preserved in layers of sediment. So what does that have to do with the temperature? Well, it turns out that foraminifera that grow in warmer waters build their shells a little differently.

DM: As the temperature gets hotter, the forams become more sloppy chemists and they allow more magnesium into their calcium carbonate shell. And so you can measure the magnesium to calcium ratio, and that's a very strong function of temperature.

LHF: And there are other time-traveling thermometers found in tree rings, ice cores, and stalagmites deep in caves. When you combine these separate lines of evidence, we can build a window into climates from long ago.

What’s more, when scientists tracked these temperature records further and further back in time, a surprising new picture appeared.

DM: They were able to see, oh wow, there hasn't just been one ice age. There's been this cycle going back and forth between ice ages and warmer periods.

So the earth has been going in and out of ice ages over the last million years at a rate of roughly one cycle per 100,000 years. So you'll have a period like the peak of the last ice age about 20,000 years ago. And then temperatures will rise into warm climates like we've enjoyed for the last 10 thousand years.

LHF: How? And why? Well, the answer, amazingly, lies not here on Earth, but out in the solar system.

So you might know that the Earth orbits the sun in an ellipsis—not a perfect circle. And the Earth is also tilted. At any time, one pole faces the sun—that’s the half of the Earth that experiences summer—and the other half faces away—that’s the Earth that experiences winter. But over thousands of years, that orbit and tilt… well, it shifts.

DM: The Earth's orbit gradually changes as we get pulled by the other planets in the solar system. And so the Earth's orbit becomes more elliptical or more circular through time. The Earth's tilt changes a little bit through time in a cyclical manner. 

LHF: And gradually, our north and south poles might find that, during the summer, they’re no longer tilted so strongly toward the sun.

DM: That decreases how much sunlight comes into the Arctic during local summer and makes it harder to melt away the previous winter’s snow and ice, and it builds up and builds up and builds up, and eventually forms an ice sheet.

So, then the question is, okay, you're building up some ice sheets in Northern Canada and Scandinavia. Why does that make the whole world cold? The real reason that ice ages are a global phenomenon is because, as you grow an ice sheet, the ice sheet changes ocean circulation in such a way that more carbon dioxide gets stored in the deep ocean rather than sticking around in the atmosphere.

LHF: You probably remember that CO2 is the most important of the heat-trapping gases in our atmosphere that are causing today’s climate change. And throughout Earth’s history there’s been a close relationship between the average temperature of our planet and the amount of CO2 in our atmosphere. Now, scientists use the tools of paleoclimate to look at how much CO2 was in the air during the ice ages. In fact, we can actually measure directly the air of the ancient past—because some of it is still around.

DM: In Antarctica in particular, as the snow builds up and then gets compressed beneath other layers of snow above it and gradually turns into ice, it traps little bubbles of air. And that air is pristine samples of the ancient atmosphere. And so scientists will collect these ice cores, bring them back to the lab, and then measure directly how much carbon dioxide is in the air from times in the past.

LHF: That’s really cool. All right, so let’s recap. So the Earth shifts slightly in space over thousands of years, making the Arctic summer darker and colder. And ice sheets form and spread, and the ocean circulation changes. This traps CO2 deep in the ocean, and because there is less heat-trapping CO2 in the atmosphere, the entire planet begins to cool.

DM: And so it's quite a chain of events that leads from the changes in Earth's orbit to the ice ages themselves.

LHF: So how much do these changes add up? Well, in the last ice age, which was 20,000 years ago, CO2 in the atmosphere fell by about a third. So do you want to guess how much the Earth cooled as a result?

DM: We now know that in the peak of the last Ice Age, it was about 10 degrees Fahrenheit colder than it was during pre-industrial times.

LHF: Did you guess correctly? Or were you way off? Maybe you’re asking yourself now—wait, what? Just ten degrees? Isn’t that the difference between a chilly fall day and a crisp spring afternoon?

DM: Yeah, it's really striking to me how different the world was, given only 10 degrees Fahrenheit difference in mean temperatures. So, where I'm sitting around Boston, Massachusetts, would have had about a mile of ice on top of me right now. 

LHF: From just 10 degrees of cooling! (Which is about five and a half degrees Celsius, by the way.) But this is the crucial difference between weather and climate. If the weather changes by 10 degrees, well, you put on a jacket. But if the average climate changes by 10 degrees… well, you’ve got the planet where woolly mammoths roamed as far south as Illinois and Spain. 

DM: And then slow changes in Earth's orbit gradually increase how much summer sunlight there is in the Arctic and start to melt back those ice sheets and the changes go in reverse. So the ocean circulation responds and allows carbon dioxide that has been stored in the deep ocean to come back into the atmosphere.

LHF: And those rising CO2 levels warm the entire world. Like they are today.

Except, not quite like today. We really are living through something that’s different now. So for one thing, today’s climate change is timed all wrong. The Earth’s position in space is not setting us up for more warming.

DM: The variations in Earth's orbit are fairly subtle right now, and then they'll get larger over the next few tens of thousands of years. So if there weren't human-caused climate change, we would eventually go back into another ice age.

LHF: And a huge difference between the end of the last ice age, and today’s warming—is how fast it’s happening.

DM: So if you look at the warming coming out of the last ice age, temperatures were low until about 17,000 years ago, and then CO2 started to rise and global temperatures started to rise. And they rose that 10 degrees Fahrenheit in about 7,000 years. Modern temperature change is about 10 times faster.

LHF: Which means that today, we’re facing climate change at a speed that even our distant, nomadic ancestors in the ice age never confronted. Let alone the more recent humans who laid the foundations of civilization as we know it.

DM: The last 10,000 years have been a period of stability in global temperatures. And that period of stability has coincided with the growth of complex human societies and the shift to agriculture as the basis for human society and you know, dramatic expansions in human population. And this I think is more than a coincidence.

LHF: It’s true that the Earth has gone through immense climate change before, many times over, in fact. But human civilization… has not. And especially not this fast.

Today, we are the ones changing the balance of our atmosphere. And we’re the ones who get to decide. Do we want to rapidly shake our planet loose from the stability that we’ve always known? Or will we be happier, and safer, if we act to preserve the climate in which humanity has flourished for the last ten thousand years?

That is our show today. Thank you to everyone who sent us in questions about the ice ages. You can send us your own question by leaving us a voicemail message at 617 253 3566 or visiting https://climate.mit.edu/ask.

Today I Learned: Climate is the climate change podcast of the Massachusetts Institute of Technology. Aaron Krol is our Writer and Executive Producer. David Lishansky is our Sound Editor and Producer. Michelle Harris is our fact-checker. The music is by Blue Dot Sessions. And I’m your Host and Senior Editor, Laur Hesse Fisher. 

Thank you Prof. David McGee for speaking with us, and to all of you, for listening. Keep up your climate curiosity.

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