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SCIENTISTS HAVE CAPTURED EARTH’S CLIMATE OVER THE LAST 485 MILLION YEARS. HERE’S
THE SURPRISING PLACE WE STAND NOW.


AN EFFORT TO UNDERSTAND EARTH’S PAST CLIMATES UNCOVERED A HISTORY OF WILD
TEMPERATURE SHIFTS AND OFFERED A WARNING ON THE CONSEQUENCES OF HUMAN-CAUSED
WARMING.

10 min
1928

First vertebrates

on land

First

mammals

Extinction of

dinosaurs

104ºF

40ºC

30

86

20

68

Global mean surface temperature

10

50

0

32

Current

geological

stage

100

485

million

years ago

390

300

225

Source: “A 485-million-year history of Earth’s surface temperature”, E.J. Judd
et al. Temperatures are averages for geological periods. Shaded area shows
values with a 68% probability.

First vertebrates

on land

First

mammals

Extinction of

dinosaurs

104ºF

40ºC

86

30

20

68

Global mean surface temperature

10

50

32

0

Current

geological

stage

100

65

485

million

years ago

390

300

225

Source: “A 485-million-year history of Earth’s surface temperature”, E.J. Judd
et al. Temperatures are averages for geological periods. Shaded area shows
values with a 68% probability.

First vertebrates

on land

First

mammals

Extinction of

dinosaurs

Global mean surface temperature

104ºF

40ºC

86

30

68

20

10

50

0

32

485 millions

year ago

390

300

225

200

100

65

Current

geological

stage

Source: “A 485-million-year history of Earth’s surface temperature”, E.J. Judd
et al. Temperatures are averages for geological periods. Shaded area shows
values with a 68% probability.

First vertebrates

on land

First

mammals

Extinction of

dinosaurs

104ºF

40ºC

Global mean surface temperature

30

86

20

68

10

50

32

0

Current

geological

stage

485 millions year ago

390

300

225

200

100

65

50

25

Source: “A 485-million-year history of Earth’s surface temperature”, E.J. Judd
et al. Temperatures are averages for geological periods. Shaded area shows
values with a 68% probability.

First vertebrates

on land

First

mammals

Extinction of

dinosaurs

40ºC

104ºF

Global mean surface temperature

30

86

20

68

10

50

0

32

Current

geological

stage

485 million years ago

390

300

225

200

100

65

50

25

Source: “A 485-million-year history of Earth’s surface temperature”, E.J. Judd
et al. Temperatures are averages for geological periods. Shaded area shows
values with a 68% probability.

By Sarah Kaplan
and 
Simon Ducroquet
September 19, 2024 at 2:01 p.m. EDT

An ambitious effort to understand the Earth’s climate over the past 485 million
years has revealed a history of wild shifts and far hotter temperatures than
scientists previously realized — offering a reminder of how much change the
planet has already endured and a warning about the unprecedented rate of warming
caused by humans.



The timeline, published Thursday in the journal Science, is the most rigorous
reconstruction of Earth’s past temperatures ever produced, the authors say.
Created by combining more than 150,000 pieces of fossil evidence with
state-of-the-art climate models, it shows the intimate link between carbon
dioxide and global temperatures and reveals that the world was in a much warmer
state for most of the history of complex animal life.

At its hottest, the study suggests, the Earth’s average temperature reached 96.8
degrees Fahrenheit (36 degrees Celsius) — far higher than the historic 58.96 F
(14.98 C) the planet hit last year.

The revelations about Earth’s scorching past are further reason for concern
about modern climate change, said Emily Judd, a researcher at University of
Arizona and the Smithsonian specializing in ancient climates and the lead author
of the study. The timeline illustrates how swift and dramatic temperature shifts
were associated with many of the world’s worst moments — including a mass
extinction that wiped out roughly 90 percent of all species and the asteroid
strike that killed the dinosaurs.

Global mean surface temperature

485

million

years ago

400

300

200

100

50

83.3ºF

28.5ºC

64.6

18.1

The largest mass extinction happened 250 million years ago, when gases from
volcanic eruptions – including CO₂ – raised Earth’s temperature by more than
18ºF (10ºC) in the span of about 50,000 years.

Global mean surface temperature

485

million

years ago

400

300

200

100

50

83.3ºF

28.5ºC

64.6

18.1

The largest mass extinction happened 250 million years ago, when gases from
volcanic eruptions – including CO₂ – raised Earth’s temperature by more than
18ºF (10ºC) in the span of about 50,000 years.

Global mean surface temperature

485 million

years ago

400

300

200

100

50

83.3ºF

28.5ºC

64.6

18.1

The largest mass extinction happened 250 million years ago, when gases from
volcanic eruptions – including CO₂ – raised Earth’s temperature by more than
18ºF (10ºC) in the span of about 50,000 years.

“We know that these catastrophic events … shift the landscape of what life looks
like,” Judd said. “When the environment warms that fast, animals and plants
can’t keep pace with it.”

At no point in the nearly half-billion years that Judd and her colleagues
analyzed did the Earth change as fast as it is changing now, she added:

“In the same way as a massive asteroid hitting the Earth, what we’re doing now
is unprecedented.”


485 MILLION YEARS OF TEMPERATURE TURMOIL

The timeline encompasses almost all of the Phanerozoic — the geologic eon that
began with the emergence of multicellular, non-microscopic organisms and
continues today.

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It portrays a global climate that was more dynamic and extreme than researchers
had imagined, said Jess Tierney, a climate scientist at the University of
Arizona and co-author of the study. Compared with graphs based solely on climate
models, which tend to depict smaller and slower swings in temperatures, the new
timeline is full of sudden spikes and abrupt shifts.

But, in keeping with decades of past research on climate, the chart hews closely
to estimates of carbon dioxide in the atmosphere, with temperatures rising in
proportion to concentrations of the heat-trapping gas.

“Carbon dioxide is really that master dial,” Tierney said. “That’s an important
message … in terms of understanding why emissions from fossil fuels are a
problem today.”

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At the timeline’s start, some 485 million years ago, Earth was in what is known
as a hothouse climate, with no polar ice caps and average temperatures above 86
F (30 C). The oceans teemed with mollusks and arthropods, and the very first
plants were just beginning to get a toehold on the land.

Temperatures began to slowly decline over the next 30 million years, as
atmospheric carbon dioxide was pulled from the air, before plummeting into what
scientists call a coldhouse state around 444 million years ago. Ice sheets
spread across the poles and global temperatures dropped more than 18 degrees
Fahrenheit (10 degrees Celsius). This rapid cooling is thought to have triggered
the first of Earth’s “big five” mass extinctions — some 85 percent of marine
species disappeared as sea levels fell and the chemistry of the oceans changed.

An even more dramatic shift occurred at the end of the Permian period, about 251
million years ago. Massive volcanic eruptions unleashed billions of tons of
carbon dioxide into the atmosphere, causing the planet’s temperature to shoot up
by about 18 F (10 C) in roughly 50,000 years. Acid rain fell across the
continents; marine ecosystems collapsed as the oceans became boiling hot and
depleted of oxygen.

“We know it to be the worst extinction in the Phanerozoic,” Tierney said. “By
analogy, we should be worried about human warming because it’s so fast. We’re
changing Earth’s temperature at a rate that exceeds anything we know about.”

The study also makes clear that the conditions humans are accustomed to are
quite different from those that have dominated our planet’s history. For most of
the Phanerozoic, the research suggests, average temperatures have exceeded 71.6
F (22 C), with little or no ice at the poles. Coldhouse climates — including our
current one — prevailed just 13 percent of the time.



This is one of the more sobering revelations of the research, Judd said. Life on
Earth has endured climates far hotter than the one people are now creating
through planet-warming emissions. But humans evolved during the coldest epoch of
the Phanerozoic, when global average temperatures were as low as 51.8 F (11 C).

Without rapid action to curb greenhouse gas emissions, scientists say, global
temperatures could reach nearly 62.6 F (17 C) by the end of the century — a
level not seen in the timeline since the Miocene epoch, more than 5 million
years ago.



“We built our civilization around those geologic landscapes of an icehouse,”
Judd said. “So even though climate has been warmer, humans haven’t lived in a
warmer climate, and there are a lot of consequences that humans face during this
time.”


A PALEONTOLOGICAL PUZZLE

The project began nearly a decade ago, when Smithsonian scientists were
developing a new fossil hall for the National Museum of Natural History. In a
departure from most other paleontology exhibits, which tend to spotlight the
strangeness of dinosaurs and other ancient creatures, the new hall sought to
draw parallels between Earth’s past and the climate shifts happening today.

But when curators decided to install a graph of Earth’s temperature during the
Phanerozoic, they realized that no single timeline existed. Although the
scientists could cobble together estimates drawn from disparate data sets and
reconstructions of shorter time intervals, the approach left a lot of room for
uncertainties and errors.

“That was not very satisfying scientifically,” said Scott Wing, the museum’s
curator of fossil plants and one of the authors of the new study. He and his
colleagues wanted to create an estimate of past climates in “a statistically
rigorous way.”




The first task was to create a database of climate proxies — bits of fossil
evidence that hint at how the world once was. For example, the variety of oxygen
found in the teeth of extinct, eel-like creatures known as conodonts reflects
the water temperature in the oceans where they lived. The chemical composition
of fats from ancient algae indicates how they constructed their cell walls to
deal with the heat.

Yet the database was restricted to evidence from the oceans, which cover only 70
percent of the planet’s surface. And each proxy could reveal the temperature
only at a particular spot at a single point in time. Even with 150,000 data
points, Judd said, it was like trying to assemble a jigsaw puzzle with only 1
percent of the pieces.

The researchers could get a better, bigger picture using a climate model — but
those simulations might vary a lot based on what assumptions they made about the
Earth’s behavior, and the scientists would have no way of knowing which result
was the right one. So the team turned to a technique called data assimilation,
which combines real-world evidence with climate models to yield more rigorous
and accurate results.

“It’s a way of mathematically integrating those handful of puzzle pieces with
those possible pictures and finding out, what’s the picture those pieces belong
to?” Judd said.

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Though data assimilation is widely employed for modern weather forecasts and has
been used to create reconstructions of temperature over shorter spans, the
timeline published Thursday is the longest and most detailed scientists have
ever produced.

It is also more accurate than other estimates, said Benjamin Mills, a
paleoclimate researcher at the University of Leeds in England who was not
involved in the study, because it uses the data assimilation approach.

“This will contribute to assessing the driving processes behind long-term
temperature changes and the natural mechanisms of stabilizing or destabilizing
Earth’s climate,” Mills wrote in an analysis that was published alongside the
timeline.


‘ALL THE THINGS WE DON’T KNOW’

The new temperature timeline raises as many questions as it answers, Wing said.
Finding global average temperatures of more than 35 degrees Celsius implies that
some parts of the planet were even hotter — during the warmest parts of the
Cretaceous, for example, average temperatures in the interiors of continents
might have reached 122 F (50 C). Even the hardiest modern species would wither
in such a sweltering environment.

“It’s an indication of all the things we don’t know about how greenhouse
climates work,” Wing said.

Perhaps organisms that evolved during hothouse eras were much better adapted to
extreme heat than the plants and animals that live today, he added. Or maybe
global temperatures were much more uniform during those periods, with few areas
getting much colder or warmer than the average.

Michael Mann, a climate scientist at the University of Pennsylvania who is known
for his analyses of past global temperatures, said he was also surprised by the
suggestion that the planet got so warm.

The finding supports many scientists’ concern that feedback loops in the Earth
system could lead to much higher temperatures than most climate models predict,
he wrote in an email. But it’s also possible that the data assimilation assumes
too much warming and is missing factors that might forestall a runaway
greenhouse effect.

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“While I applaud the authors for this ambitious and thoughtful study, I am
skeptical about the specific, quantitative conclusions,” Mann said.

Wing acknowledged that there is a lot more work to do. He and his colleagues aim
to continue to refine the timeline by adding data from land-based proxies, such
as fossil leaves. They also hope it will help researchers trying to model future
climate change by allowing them to examine warmer periods from Earth’s past.

And for the billions of people who are now living through the hottest years ever
recorded — and facing a hotter future still — Judd said the timeline should
serve as a wake-up call. Even under the worst-case scenarios, human-caused
warming will not push the Earth beyond the bounds of habitability. But it will
create conditions unlike anything seen in the 300,000 years our species has
existed — conditions that could wreak havoc through ecosystems and communities.

“As long as one or two organisms survive, there will always be life. I’m not
concerned about that,” Judd said. “My concern is what human life looks like.
What it means to survive.”


MORE ON CLIMATE CHANGE

Understanding our climate: Global warming is a real phenomenon, and weather
disasters are undeniably linked to it. As temperatures rise, heat waves are more
often sweeping the globe — and parts of the world are becoming too hot to
survive.

What can be done? The Post is tracking a variety of climate solutions, as well
as the Biden administration’s actions on environmental issues. It can feel
overwhelming facing the impacts of climate change, but there are ways to cope
with climate anxiety.

Inventive solutions: Some people have built off-the-grid homes from trash to
stand up to a changing climate. As seas rise, others are exploring how to
harness marine energy.

What about your role in climate change? Our climate coach Michael J. Coren is
answering questions about environmental choices in our everyday lives. Submit
yours here. You can also sign up for our Climate Coach newsletter.



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