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Monday, December 12, 2022

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Poles Apart

Earth Had a Dangerous Axis Tilt 84 Million Years Ago, Shows Research

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Oct 20, 2021

Scientists know Earth tilts from time to time on its axis. But just how often this has happened, and what this means, remains a longstanding geological debate. Evidence found in Italy shows the Earth tilted around 12 degrees 84 million years ago. This was the time when dinosaurs were alive. But the Earth corrected itself quickly. To put this into context: the tilt would have displaced continents by 1,000s of miles, enough to push New York City to where Tampa, Florida is now.

An April study found that a similar tilt like the one from 84 million years ago is currently happening, courtesy of climate change.

The Earth is made up of a metal inner core and has a liquid metal outer core. Hugging this outer core is a solid mantle and the crust (the surface on which we live). “All of this is spinning like a top, once per day,” Phys.org explained. The planet spins around an imaginary line, passing through the North and South Pole, called its spin axis. The Earth’s crust is fragmented into tectonic plates; becoming the foundation for continents and oceans.

According to the “true polar wander” (TPW) theory, some scientists argue that the outer mantle and crust can wobble and slide over the Earth’s liquid metal core. In other words, the crust and mantle rotated around the Earth’s outer core (also shifting the geographical poles and causing the planet to tilt itself) and slipped back. Think of a solved puzzle on a table; the minute the surface shakes, the pieces change position.  

“This observation represents the most recent large-scale TPW documented and challenges the notion that the spin axis has been largely stable over the past 100 million years,” the researchers explain in their paper published in Nature Communications earlier this year. And while it tilted, it also snapped back quickly (over some five million years) — what the researchers called a “cosmic yo-yo.”

“The planet’s outer layer behaves elastically like a rubber band and would have snapped back to its original shape after the excursion,” Ross Mitchell, a geophysicist at the Chinese Academy of Sciences and a co-author, told Insider.

 

The tilting doesn’t alter the Earth’s magnetic field. Instead, the core’s shifting rocks generate paleomagnetic data, which helps scientists track the location and direction of the North and South poles. “Although scientists can measure true polar wander occurring today very precisely with satellites, geologists still debate whether large rotations of the mantle and crust have occurred in Earth’s past,” Phys.org added.

The evidence does two things: it challenges the idea that Earth’s spin axis has been stable over the last 100 million years, and the process may have started during the Late Cretaceous period. Some studies have argued there is limited geological record to show Earth was tipping over back then. The latest research plugs that hole. “That is one reason why it is so refreshing to see this study with its abundant and beautiful paleomagnetic data,” said geophysicist Richard Gordon, from Rice University in Houston, who wasn’t involved in the study.

The Earth tipping means continents and rocks at the core are displaced. According to the findings, tilting would have shifted Italy to the equator before the Earth tipped back. “We never suspected we would see this full round-trip event,” Mitchell said.

Any tipping around the axis influences climate patterns. “Whole portions of the planet could be plunged into darkness or thrown into direct sunlight for months at a time,” if the axial tilt were to change enough, Green Matters argued. For instance, if Earth’s axis tilted to 90 degrees, extreme seasons could accelerate climate change and its impact on every continent (like the Northern Hemisphere experiencing nearly 24 hours of sunlight for months).

 https://theswaddle.com/earth-had-a-dangerous-axis-tilt-84-million-years-ago-shows-research/

 

Why is the Earth Tilted? New Theory Offers Clues on a Dizzy Moment

The story of the Earth and its moon has traditionally started with the “big whack,” a collision between proto-Earth and a Mars-sized planet about 4.5 billion years ago that nearly vaporized them both and knocked enough debris into orbit to form the moon. Now, new evidence suggests that this impact also sent Earth into a very tight spin with a very sharp axial tilt, nearly perpendicular to the equator. And it just might be that this dizzy moment in our planet’s history was fundamental to the creation of the conditions that support life.

 

The groundbreaking study out of the University of Maryland, published online Monday in Nature, provides the most complete explanation for the fact that the moon’s orbit is about five degrees off kilter from Earth’s orbital path around the sun.

“This large tilt is very unusual. Until now, there hasn’t been a good explanation,” says Astronomy Professor Douglas Hamilton, one of the paper’s authors, in a release. But we can understand it if the Earth had a more dramatic early history than we previously suspected.”

In the old model, Earth’s current axial tilt of 23.5 degrees resulted from the angle of the collision that formed the moon, and has stayed that way through time. Over billions of years, Earth’s rotation slowed from five hours to 24 as tidal energy was released.

In the “giant impact” model of the moon’s formation, the young moon began its orbit within Earth's e...
Before now, scientists assumed there was a gradual transition for the moon's move from Earth's equatorial to ecliptic plane.Douglas Hamilton/UMD

The new model is a lot more complicated, but it explains things that couldn’t be explained by the previous one, especially the moon’s orbital tilt. In this story, after the big whack, Earth spun around every two hours and was tilted a dramatic 70 degrees. This helps support evidence that the collision that formed the moon would have had to have been extremely violent — violent enough to turn most of Earth into a cloud of vaporized rock, which explains the similar composition of the Earth and the moon.

Collisional physics suggests the moon would have condensed from the vaporized material along Earth’s equatorial plane, and then transitioned to its ecliptic plane over time because of the sun’s gravitational pull. But in this scenario, with a highly tilted and fast-spinning Earth, that doesn’t happen right away. Instead, tidal flexing that resulted from the moon’s varying distance from the Earth kept the two locked in a sort of stalemate, which could have lasted millions of years.

Through this period the Earth’s rotation would have gradually slowed, until the stalemate was broken and the moon proceeded to travel out towards the sun. This would have caused a righting of the Earth’s axis, and the moon would have oscillated back and forth across the Earth’s ecliptic plane, with these oscillations growing smaller over time as the moon moves further from Earth and energy is dissipated through tides. The moon’s current five-degree tilt of the ecliptic plane is an expression of that continued oscillation.

This story shows how the formation of the moon is tied up with the Earth’s current axial tilt, which is responsible for climate-moderating seasons on this planet. It could be that planets elsewhere with large moons may have gone through this same process, which could make for conditions suitable for the emergence of alien life.

“Despite smart people working on this problem for 50 years, we’re still discovering surprisingly basic things about the earliest history of our world,” says Matija Cuk, a scientist at the SETI Institute and lead researcher for the simulations, in a news release. “It’s quite humbling.

 https://www.inverse.com/article/23062-earth-moon-history-axis-tilt

 Science

Ask Ethan: Will Earth’s Temperature Start Decreasing Over The Next 20,000 Years?

Ethan Siegel
Senior Contributor

 

According to our best understanding of Earth’s climate, the global average temperature has increased significantly over the past ~140 years: the amount of time for which a reliable, direct temperature record exists. It’s widely accepted that the driving force behind this increase is the human-caused emission of greenhouse gases such as CO2, which has increased in atmospheric concentration by about 50% from the pre-industrial levels that were present early in the 1700s. But humans aren’t the only entities that affect Earth’s climate; there are natural variations that occur in the Earth-Sun system. Will they cause Earth’s temperature to decrease in the relatively near future? That’s what Ian Graham wants to know, as he writes in to ask:

“I'm trying to get my head around the Earth's axial tilt and the ramifications of the current 23.5 degree increase/decrease, and trying to understand Milankovitch's theory. If the Perihelion is increasing and the earth warms as a result, ignoring the greenhouse effects of humans, what is the effect of both the Perihelion increase and the movement of earth away from the Sun? My thought is the Earth's global temp should decrease over the next 20,000 years.”

There’s a lot to unpack here, so let’s start at the beginning: with Milankovitch himself.

 

Back in the early 1900s, Serbian astrophysicist Milutin Milankovitch decided to work on a puzzle that no one else had successfully solved: linking the physics that governed the Solar System with the theory of Earth's climate. As the Earth orbits the Sun, you'll barely notice any year-to-year changes, as they're relatively minuscule. Sure, the phases of the Moon shift, the exact date and time of equinoxes and solstices vary, and timekeeping requires the regular insertion of leap days to keep the seasons aligned with our calendar.

 https://www.forbes.com/sites/startswithabang/2020/10/16/ask-ethan-will-earths-temperature-start-decreasing-over-the-next-20000-years/?sh=3f14e342643e

 

While Newton’s law of gravitation and Kepler’s laws of planetary motion are relatively simple, however, anything more complex than the simplest system imaginable can lead to incredibly elaborate orbital complications. In the case of the Earth, it’s affected by:

  • the fact that it rotates on its axis,
  • it moves in an ellipse, rather than a circle, around the Sun,
  • it has a large, natural satellite: the Moon,
  • which in turn orbits the Earth tidally locked, inclined at an angle to Earth’s orbit and axial rotation, and in a quite eccentric ellipse,
  • and the small (but not completely negligible) gravitational influence of the other bodies in our Solar System.

All of these effects interplay with one another to determine the long-term evolution of Earth’s orbit.

There are a few important rules at play. One is the law of gravitation, and the fact that these aren’t point-like objects we’re talking about, but rather spheroids: physical objects of a real, finite size and with intrinsic angular momentum to them. That angular momentum, for each object in our Solar System — and particularly for the Earth, Moon, and Sun — is split up into the spin of each body, or its rotational motion, and its orbital angular momentum, or its revolutionary motion. (Yes, even the Sun doesn’t remain stationary, but rather makes its own “wobbly” motion due to the gravitational influence of the other bodies in the Solar System.)

What Milankovitch found, perhaps surprisingly to some, is that these effects all add up to cause three major long-term variations, arising from the interactions of these Solar System bodies.

  1. Precession, or the fact that the direction that Earth’s axis points rotates over time.
  2. Axial tilt, which changes ever so slightly from its current 23.5° over time.
  3. Eccentricity, or how circular vs. elliptical Earth’s orbit is.

Although there are other effects, they’re all minor compared to these three major ones. Let’s look at them individually.

1.) Precession. This one is actually pretty straightforward: the Earth spins on its axis, which is inclined at 23.5° with respect to our revolutionary path around the Sun. When our axis is pointed perfectly perpendicular to the line connecting the Earth to the Sun, we experience equinoxes; when the axis is pointed along the Earth-Sun line, we experience solstices. Although the timing of both equinoxes and solstices would change over time, astronomically, the insertion of leap days keeps the equinoxes centered around March 21 and September 23, with the solstices occurring around December 21 and June 21.

But the physical direction that our axis point does, in fact, change over time. Right now Polaris is our “north star” because our axis points towards it to within 1°, which is remarkable but unusual for a bright star. Over long periods time, the direction that Earth’s rotational axis points will make a complete circle, as two effects both come into play:

  • our axial precession, which is Earth’s “wobble” relative to the stars, largely due to the Moon and Sun,
  • and our apsidal precession, which is how Earth’s ellipse “wobbles” as we orbit the Sun, primarily due to Jupiter’s and Saturn’s influences.

Axial precession causes Earth to make a full 360° turn on its axis every 25,771 years, while the apsidal precession leads to an additional 360° turn (in the same direction) every ~112,000 years or so. For an observer on Earth, if we could live that long, we’d see the pole stars change in a periodic fashion every 23,000 years or so, as these effects combine in an additive fashion. Thousands of years ago, the star Kochab (the brightest star in the Little Dipper’s bowl) was where our North Pole pointed; thousands of years from now, it will point at Vega, one of the brightest stars in the sky, 13,000 years in the future.

The main effect of this precession on temperature is seasonal, however, and has no long-term effect on an annual basis. Because the South Pole points towards the Sun close to the December solstice, orbital perihelion aligns with its summer and aphelion is close to its winter, resulting in colder winters and hotter summers compared to the Northern Hemisphere. This will change over time with a ~23,000 year period, but presents no long-term, overall temperature variations.

2.) Axial tilt. At present, the Earth rotates on its axis at an angle of 23.5°, and that axial tilt plays a more significant role than even how close or far we are from the Sun in determining our seasons. When the Sun’s rays are more direct on our portion of the Earth, we receive more energy from the Sun; when they’re more indirect (incident at a lower angle and passing through more of our atmosphere), we receive less energy. Over the course of a year and averaged over the whole planet, our axial tilt doesn’t substantially affect how much total energy the Earth receives.

But our axial tilt does vary somewhat over long periods of time: from a minimum of 22.1° to a maximum of 24.5°, oscillating from its minimum to maximum and back to minimum again approximately every ~41,000 years. Our Moon is primarily responsible for stabilizing our axial tilt; the tilt of Mars is comparable to that of Earth, but Mars’s variations are about 10 times as great, because it lacks a large, massive moon to keep these axial tilt variations small.

Although the total energy received by our planet — and hence, Earth’s total temperature — isn’t affected by our axial tilt, the energy received as a function of latitude is very sensitive to it. When our axial tilt is lower, a greater percentage of the energy received by Earth is concentrated towards equatorial latitudes, while when it’s greater, less energy is received at the equator and more is incident on the poles. As a result, larger axial tilts favor the retreat of glaciers and polar ice sheets, while smaller axial tilts generally favor their growth.

Right now, our axial tilt is about midway between these two extremes, and in the process of decreasing. Our axial tilt last reached its maximum value nearly 11,000 years ago, corresponding to the end of our last glacial maximum, with our next minimum approaching in a little under 10,000 years. If natural variations were dominant, we’d expect the next ~20,000 years to favor the growth of ice sheets. As NASA’s website says:

“As obliquity decreases, it gradually helps make our seasons milder, resulting in increasingly warmer winters, and cooler summers that gradually, over time, allow snow and ice at high latitudes to build up into large ice sheets. As ice cover increases, it reflects more of the Sun’s energy back into space, promoting even further cooling.”

This, very likely, is where the notion that Earth should start cooling again comes from.

3.) Eccentricity. This effect, of all the effects caused by the dynamics experienced by Earth in the Solar System — gravitational forces, tides, angular momentum exchange, etc. — is the only one that changes the total amount of solar energy received by the Earth on an annual basis. Due largely to the gravitational tug of the gas giants, the eccentricity of Earth’s orbit (or how elongated its ellipse is, e, which is 0 for a perfect circle and approached 1 for an extremely long, skinny ellipse) varies in two ways:

  • with a periodicity on 100,000 year timescales, going from almost-perfectly circular orbits (e = 0) to near-maximum ellipticity,
  • and with additional slight magnifications every 400,000 years, leading to Earth’s orbit achieving its maximum ellipticities of all (e = 0.07).

Earth, right now, has a relatively small eccentricity: 0.017, which is close to the minimum value. Our closest approach to the Sun, perihelion, is only 3.4% closer than our farthest position, aphelion, and we receive just 7% more radiation from the Sun in that configuration. On the other hand, when our eccentricity is maximized, perihelion and aphelion differ by thrice that amount, with the difference in radiation received at perihelion vs. aphelion rising to 23%.

When our orbit is more eccentric, our seasons can even become dominated by our orbital position, rather than our axial tilt. However, that’s unlikely to happen anytime soon. Right now, our eccentricity is close to the minimum, and is decreasing further: towards zero. And in general, higher eccentricity — a more elliptical orbit as compared to a more circular one — means a greater amount of solar radiation received by Earth over the course of a year.

  • The maximum amount of radiation Earth can receive occurs when our eccentricity is maximized, and we can call that “100%” of maximum.
  • For a perfectly circular orbit, we’d still receive 99.75% of that maximum amount.
  • For where we are right now in our orbit, we receive almost that same value: 99.764%, which is presently decreasing towards that 99.75% value.

There is a slight decrease that’s in progress, but it’s so minuscule that it’s practically negligible — as are all of these cumulative effects — in comparison to the enormous changes brought on by the human-caused greenhouse gas contribution to global temperature.

Looking at the effects of Earth’s orbital changes quantitatively — including all three effects of precession, axial tilt, and elliptical eccentricity — so clearly illustrates the incredible conundrum facing humanity today. Because of the increased concentration of greenhouse gases, Earth’s average global temperature has increased by approximately 0.98°C (1.76°F) since 1880: an increase of approximately 0.33% in the average energy retained by the Earth. This human-caused effect has, by far, the dominant impact on Earth’s climate of all of these factors.

The increased energy retention due to atmospheric changes dwarfs the coming 0.014% decrease in received energy arising from the change in our ellipse’s shape, and overwhelms the axial tilt changes, which redistribute only an extra 0.0002% of the polar energy towards the equator with each passing year. It even dwarfs the 0.08% variation that occurs coincident with the 11-year sunspot cycle. Unless we address the human factors which currently dominate the changing climate of Earth, these natural factors — important and real though they may be — will be overwhelmed by our own recklessness.

https://www.forbes.com/sites/startswithabang/2020/10/16/ask-ethan-will-earths-temperature-start-decreasing-over-the-next-20000-years/?sh=3f14e342643e

 

What would happen if the tilt of the earth was 0 degrees?

 
 
Dec 16, 2015

The days and nights would be about the same length and there would be no seasons.

Explanation:

The axial tilt causes the days to be longer than the nights in Summer and shorter in Winter. It also causes the seasons as one hemisphere gets more sunlight during its Summer and less during its Winter.

It the tilt angle was zero, then the days and nights would stay at the same length and there would be no seasons.

The higher latitudes would not get the extremes of weather that they get now. It would have a big impact on migratory animals as there would be no need to migrate.

https://socratic.org/questions/what-would-happen-if-the-tilt-of-the-earth-was-0-degrees

Environment

What Thawed the Last Ice Age?

The relatively pleasant global climate of the past 10,000 years is largely thanks to higher levels of atmospheric carbon dioxide

 

Roughly 20,000 years ago the great ice sheets that buried much of Asia, Europe and North America stopped their creeping advance. Within a few hundred years sea levels in some places had risen by as much as 10 meters—more than if the ice sheet that still covers Greenland were to melt today. This freshwater flood filled the North Atlantic and also shut down the ocean currents that conveyed warmer water from equatorial regions northward. The equatorial heat warmed the precincts of Antarctica in the Southern Hemisphere instead, shrinking the fringing sea ice and changing the circumpolar winds. As a result—and for reasons that remain unexplained—the waters of the Southern Ocean may have begun to release carbon dioxide, enough to raise concentrations in the atmosphere by more than 100 parts per million over millennia—roughly equivalent to the rise in the last 200 years. That CO2 then warmed the globe, melting back the continental ice sheets and ushering in the current climate that enabled humanity to thrive.

That, at least, is the story told by a new paper published in Nature on April 5 that reconstructs the end of the last ice age. Researchers examined sediment cores collected from deep beneath the sea and from lakes as well as the tiny bubbles of ancient air trapped inside ice cores taken from Antarctica, Greenland and elsewhere. (Scientific American is part of Nature Publishing Group.) The research suggests that—contrary to some prior findings—CO2 led the prior round of global warming rather than vice versa, just as it continues to do today thanks to rising emissions of CO2 and other greenhouse gases.

"We find that global temperature lags a bit behind the CO2 [levels]," explains paleoclimatologist Jeremy Shakun, a National Oceanic and Atmospheric Administration fellow at Harvard and Columbia universities, who led the research charting ancient CO2 concentrations and global temperatures. "CO2 was the big driver of global warming at the end of the Ice Age."

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Shakun and his colleagues started by creating the first global set of temperature proxies—a set of 80 different records from around the world that recorded temperatures from roughly 20,000 years ago to 10,000 years ago. Ranging from the magnesium levels in microscopic seashells pulled from ocean sediment cores to pollen counts in layers of muck from lakebeds, the proxies delivered thousands of temperature readings over the period. "Ice cores only tell you about temperatures in Antarctica," Shakun notes of previous studies that relied exclusively on an ice core from Antarctica that records atmospheric conditions over the last 800,000 years. "You don't want to look at one spot on the map for global warming."

Comparing the global set of temperature records with the levels of CO2 in the ancient air bubbles trapped in ice cores reveals that global average temperatures started to rise at least a century after CO2 levels began to creep up. That's the reverse of what seems to have happened in Antarctica, where warming temperatures precede rising CO2 levels. But that local warming may be explained by this shutdown of ocean currents as a result of massive glacial melt in the Northern Hemisphere—a result further reinforced by computer modeling using the data gathered from the real-world record.

The reason for the retreat of the ice sheets remains elusive, however. Whereas there was a change in the relative strength of the sun roughly 20,000 years ago thanks to variations in the planet's orbit, it was smaller than changes that preceded it and failed to trigger a melt. In fact, ice cores from Greenland suggest there was an even larger warming event in the north roughly 60,000 years ago, notes climate scientist Eric Wolff of the British Antarctic Survey in a comment on the findings also published in Nature.

"We know that the only thing changing in the Northern Hemisphere [20,000 years ago] were these orbital changes" that affect the amount of sunlight striking the far north, explains geologist Peter Clark of Oregon State University, who guided Shakun's research. The melting in the north could have been triggered "because the ice sheets had reached such a size that they had become unstable and were ready to go." This may also help explain the cyclical rise and fall of ice ages over hundreds of thousands of years.

Just where the extra carbon dioxide came from remains unclear as well. "There is no convincing evidence that a sufficiently large reservoir of old metabolic carbon existed in some mysterious location in the glacial ocean only to be ventilated during deglaciation," argues paleoclimatologist Lowell Stott of the University of Southern California, who was not involved in the study. But a paper published online in Science on March 29 suggests that the extra CO2 did come from the Southern Ocean, based on analysis of the isotopes of carbon embedded in the molecule most responsible for global warming. Stott also argues that the timing of the warming versus that of increasing CO2 levels remain too close to be sure which came first.

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Of course, modern global warming stems from a clear cause—rising levels of CO2 (and other greenhouse gases) from fossil fuel burning, cutting down forests and other human activities. And, in the past rising CO2 levels at the very least magnified global warming, ushering in the relatively balmy, stable climate sometimes called the "long summer" that has allowed human civilization to flourish. Humanity has now raised global CO2 levels by more than the rise from roughly 180 to 260 ppm at the end of the last ice age, albeit in a few hundred years rather than over more than a few thousand years. "The end of an ice age, you have a sense in your bones what that means: a big, significant change for the planet," Shakun says. "It's a tangible example of what rising CO2 can mean for the planet over the long-term."

In fact, the amount of global warming already guaranteed by existing concentrations of CO2 in the atmosphere—392 ppm and still rising—will also play out over centuries, if not millennia. "The rise at the end of the Ice Age and today is about the same [a rise of 100 ppm] and we're going to be well above and beyond," most likely increasing concentrations of greenhouse gases by hundreds of parts per million from preindustrial levels, Shakun notes. "We will only see some of that realized in this next century. It will be many centuries and beyond to feel the full effects."

 https://www.scientificamerican.com/article/what-thawed-the-last-ice-age/

Earth

Explainer: Understanding ice ages

Changes in Earth’s orbit around the sun play big roles in determining when the planet experiences a deep-freeze or thaw

Earth’s climate is ever-changing. At least several times in the past, a layer of ice has smothered much if not all of the planet’s surface — including its seas. The most recent time such a “Snowball Earth” existed was about 635 million years ago. At other times, global temperatures have soared so high that little if any ice remained anywhere, even near the poles. (A brief one of these so-called Hothouse Earth episodes developed about 56 million years ago.)

But those are the extremes. For most of Earth’s recent history, the planet’s surface has been subjected to a mix of hot and cold. Which has dominated — and for how long — has varied. It has tended to depend on several key factors.

One of the most important is how effectively Earth’s atmosphere traps the sun’s energy.

When the air contains large amounts of planet-warming gases, such as methane and carbon dioxide, global temperatures can soar. (In the distant past, levels of both gases often rose due to widespread volcanic activity. Today, carbon dioxide levels are rising because people burn fossil fuels in vehicles and power plants.)  

a map showing ice sheets during the last ice age
At the height of the last ice age, about 20,000 years ago, ice sheets in the Northern Hemisphere (Eurasia at upper right, North America at lower left) covered their largest area. Abe-Ouchi et al., Nature (2013)

Generally, when levels of these gases fall, so do temperatures across the globe. (There are exceptions, however. The gradual erosion of mountains can trigger chemical reactions that can remove carbon dioxide from the air. That, too, can trigger a long-term cooling.)

Starting about 2.6 million years ago, Earth experienced a number of ice ages. Those cool spells — possibly 40 or more of them — didn’t cause the entire planet to freeze, as likely happened in Snowball Earth eras. But these extra-cool periods did trigger the formation of large, thick sheets of ice in some parts of the Arctic. The largest and thickest ice sheets were centered over eastern Canada. But during the peaks of some ice ages, the ice spilled south into what is now the United States. The most recent ice age ended about 12,000 years ago.

In North America, the last four ice-age cycles lasted about 100,000 years each. That includes a roughly 10,000-year warm spell between each ice age. So, the ice ages themselves lasted, on average, about 90,000 years. During each cold spell, the ice sheet gradually grew to large size. Then it retreated suddenly and disappeared.

For a long while, scientists wondered what caused this pattern. Then a Serbian scientist named Milutin Milanković (Mih-LAN-koh-VITCH) noted that the pattern appeared tied to long-term changes in Earth’s orbit around the sun. Scientists now recognize orbital features can play a major role in long-term shifts in climate.

Several cycles of ice sheet growth and demise can be seen in here.

Changing orbits and tilts

Earth’s orbit is largely stable (thankfully!). Yet there are small changes in certain aspects of Earth and its orbit that vary in predictable ways, Milanković noted. Importantly, all of these changes affect the strength of sunlight reaching Earth’s surface.

One aspect of the orbit is its eccentricity (Ek-sin-TRISS-ih-tee), or roundness. At times, the planet’s orbit is almost perfectly circular. At others, its path around the sun becomes more like a slightly squished oval. When the orbit is its most squished, Earth’s distance from the sun at its farthest is about 3 percent further than when it is at its closest point for the year.

That might not seem like a lot, but it means that the sunlight falling on the planet is about 6 percent stronger in some seasons than in others. More sunlight will contribute to greater warmth. It takes about 100,000 years for Earth’s orbit to vary from near-circular to squished and then back again to near-circular. This change stems, in large part, from the gravitational tuggings exerted on Earth by Jupiter and Saturn, the largest planets in our solar system.

an illustration of the wobble of Earth's North pol
The 26,000-year-long cycle of precession, or wobble, of Earth’s North Pole through the heavens is just one factor affecting the amount of sunlight striking the Northern Hemisphere and influencing the coming and going of recent ice ages. Mysid, NASA/Wikimedia Commons

Another slowly varying aspect of Earth’s orbit is the tilt of the planet’s axis. Right now, the line that runs through Earth’s north and south poles is tilted about 23.5° from the direction that our planet travels around the sun. This tilt, known as obliquity [Oh-BLIK-wih-tee], gives Earth its seasons.

For instance, when the North Pole is generally pointed toward the sun, the Northern Hemisphere receives sunlight more directly and experiences warmer months. It takes about 41,000 years for Earth’s axis to shift from a tilt of 22.1° to 24.5° and then back again. When the axial tilt is at the low end of its range, Earth’s seasons are more even. Summers aren’t too hot; winters don’t get as cold. But when the tilt is higher than average, the temperature shifts between summer and winter become more extreme.

Finally, Earth slowly wobbles as it rotates. Right now, our planet’s North Pole constantly points toward a spot near a star named Polaris. (That’s why this star is also commonly known as the North Star. Hikers and ship captains in the Northern Hemisphere often use Polaris to help them navigate, because it always sits in the same spot in the night sky.) But because Earth isn’t a perfect sphere and its axis is tilted, the gravitational pulls of the sun and moon cause Earth’s axis to wobble. (The motion, called precession, is similar to a spinning top wobbling on a tabletop as it slows down.) It takes about 26,000 years for Earth to complete one wobble.

These three cycles — of eccentricity, obliquity and precession — have different lengths. In some instances they line up. Most of the time, they do not. (Like waves on a pond or the sea, sometimes the planet-warming effects of these cycles stack up and reinforce each other. At other times, they may tend to cancel each other out.) For the Northern Hemisphere’s ice sheets, the biggest factor affecting their growth is the amount of summer sunlight in the Arctic, scientists say. When the summer sun is relatively weak, some of the snow that fell in the previous winter may not melt. Then slowly, year by year, snow starts to build up. In time, an ice sheet will amass that grows thicker and spreads farther.  

After an ice sheet develops . . .

Once ice sheets start to grow, another factor kicks in. It too will help snow accumulate. We’re referring to the amount of sunlight that the ground reflects back into space. Scientists call this Earth’s albedo. White surfaces reflect more sunlight — a source of heat — than do dark surfaces. So an ice sheet will tend to stay cooler than will bare rocks and soil. Snow and ice also last longer when temperatures are cooler. That means that once ice sheets start to grow, they help themselves grow even more.

This ability of one factor to reinforce another is called a feedback. And here, the buildup of snow whitens the ground — increasing its albedo. This, in turn, reflects more of the sunlight that might otherwise have fostered melting.

Together, eccentricity, obliquity and precession join to make one cycle that lasts about 100,000 years. That roughly matches the length of recent ice-age cycles in North America, scientists have noted. But that match did not explain why ice ages start gradually but end suddenly.

In 2013, some researchers offered a possible explanation. They used computers to predict the warming from sunlight that falls on Arctic regions. They also included a second factor, the effect of a gradually growing ice sheet on Earth’s crust.

a diagram showing long term changes in axial tilt
Long-term changes in Earth’s axial tilt, or obliquity, is just one factor affecting how much sunlight strikes Earth’s Northern Hemisphere, which influences the coming and going of ice ages. Every 41,000 years or so, Earth’s obliquity ranges from 22.1° to 24.5° and then back again. Dna-webmaster, NASA/Wikimedia Commons

Explaining abrupt ends

When an ice sheet first starts to grow, it doesn’t weigh much. But an ice sheet 3 kilometers (almost 2 miles) thick will be crushingly heavy. In fact, it causes Earth’s crust to sag down about 1 kilometer (around 0.6 mile). Even though the sagging will be largest beneath the center of the ice sheet, the edges, too, will dip to lower altitudes. And that has a very important effect: Because temperatures at lower altitudes are warmer than those higher up, the heavier an ice sheet becomes, the more likely it is to melt around the edges.

Once all three of the orbital cycles team up to provide maximum warmth, an ice sheet will melt away. Indeed, it will disappear before Earth’s crust can spring back upward to cool and save it.

Later, after Earth’s crust has risen back close to its normal level and the three orbital cycles gradually move out of sync, Northern Hemisphere summers cool off a bit and ice sheets again can begin to grow. The researchers reported their findings in the August 8, 2013, Nature.

That’s one possible explanation for the gradual growth and sudden demise of ice sheets, scientists say. Here’s another possibility: A thicker ice sheet more effectively traps heat coming up to the surface from Earth’s interior. That, in turn, helps melt ice at the bottom of an ice sheet. That melting then helps the ice sheet flow like a glacier, become thin at the edges and melt back even more.

Other factors surely play roles in the growth and demise of ice sheets. For instance, ice sheets typically trigger changes in weather patterns across broad regions, scientists have shown. Some areas don’t get as much rainfall as before. This makes them dry up and produce lots of dust. If that dust gets swept up into the air and later falls on the ice sheet, it will darken the ice. That ice will now absorb more sunlight. This will make it melt more quickly than if it were clean. (There’s the albedo effect again!)

Finally, how much carbon dioxide exists in Earth’s atmosphere can affect temperatures near the surface. Right now, the average global concentration of that planet-warming gas is almost 400 parts per million (it was 396 ppm in 2013). It had ranged only between 180 and 280 ppm for the last 400,000 years. But then people began adding large amounts of carbon dioxide to the atmosphere, starting in the 1700s, with the beginning of the Industrial Revolution.

According to Earth’s orbital cycles, our planet might be overdue for the next ice age. But with so much carbon dioxide now in the atmosphere, that ice age might not arrive for a very long time — if it comes at all.

albedo   The percentage of radiation falling upon an object that is reflected. In astronomical terms, albedo is the percentage of sunlight that an object bounces back into space.

axis  The line about which something rotates. On a wheel, the axis would go straight through the center and stick out on either side.

carbon dioxide  A colorless, odorless gas, also known as CO2, produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

climate   The weather conditions prevailing in an area in general or over a long period.

crust    (in geology) Earth’s outermost surface, usually made from dense, solid rock.

eccentricity     (in astronomy or geometry) The degree to which a shape (or orbit) is elongated and not purely circular.

ellipse  An oval curve that is geometrically a flattened circle.

erosion    The process that removes rock and soil from one spot on Earth’s surface, depositing it elsewhere. Erosion can be exceptionally fast or exceedingly slow. Causes of erosion include wind, water (including rainfall and floods), the scouring action of glaciers and the repeated cycles of freezing and thawing that occur in many areas of the world. 

feedback  A process or combination of process that propel or exaggerate a change in some direction. For instance, as the cover of Arctic ice disappears with global warming, less of the sun’s warming energy will be reflected back into space. This will serve to increase the rate of Earth’s warming. That warming might trigger some feedback (like sea-ice melting) that fosters additional warming.

glacier  A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.

gravity  The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

ice age  Earth has experienced at least five major Ice Ages, which are prolonged periods of unusually cold weather experienced by much of the planet. During that time, which can last hundreds to thousands of years, glaciers and ice sheets expand in size and depth. The most recent Ice Age peaked 21,500 years ago, but continued until about 13,000 years ago.

ice sheet  The broad blanket of ice, most of it kilometers deep, that covers most of Antarctica. An ice sheet also blankets most of Greenland.

Industrial Revolution  A period of time in the early 1800s marked by new manufacturing processes and a switch from wood to coal and other fossil fuels as a main source of energy.

methane  A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.

obliquity   Also known as axial tilt, obliquity is the angle between a planet’s rotational axis (the line running through its north and south poles) and a line perpendicular to the plane in which the planet orbits.

orbit  The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

orbital eccentricity  The degree to which a planet’s orbit deviates from a perfect circle.

parts per million (billion or trillion)  Frequently abbreviated as ppm (or ppb or ppt), it is a measure of the number of units of some material that it mixed into another. The units should be the same (or equivalent) for both materials. The term is used to describing extremely small concentrations of one chemical dissolved in another. For example, a solution of 300 parts per billion of sodium in water would mean that there are 300 sodium atoms for every billion water molecules.

planet  A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish       ball and it must have cleared other objects out of the way in its orbital neighborhood. Based on that definition, the International Astronomical Union ruled in August 2006 that Pluto did not qualify. The solar system now consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

precession  A change in the orientation of the rotational axis of a rotating body. Earth’s rotational axis (the line running through its north and south poles) precesses, drawing a complete circle in the heavens once every 26,000 years. This precession, or wobble, is one of the factors influencing the comings and goings of recent ice ages.

sync (short for synchrony or synchronize)  To work together in harmony at the same time or rate, like in a marching band.

Citations

D. Fox. “The oldest place on Earth.” Science News for Students. June 13, 2012.

S. Ornes. “Sudden big chill.” Science News for Students. Feb. 28, 2012.

A. Witze. “Ice on the move.” Science News for Students. April 16, 2011.

S. Gaidos. “Antarctica warms, which threatens penguins.” Science News for Students. February 2, 2009.

D. Fox. “Where rivers run uphill.” Science News for Students. September 8, 2008.

E. Sohn. “Life under ice.” Science News for Students. February 9, 2007.

S. Perkins. “L.A.’s Oldest Tourist Trap.” Science News. Jan. 24, 2004.

Original Research Paper: A. Abe-Ouchi et al. Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume. Nature, Volume 500, August 8, 2013, p 190. doi:10.1038/nature12374.

 
 https://www.snexplores.org/article/explainer-understanding-ice-ages
 

Ice Age - Definition & Timeline - HISTORY https://www.history.com › topics › pre-history › ice-age Mar 11, 2015 — An ice age is a period of colder global temperatures and recurring glacial ... precession and axial tilt affected solar radiation levels, ... Missing: globe ‎| Must include: globe The Coming and Going of an Ice Age | AMNH https://www.amnh.org › videos › earth-and-climate › th... The glaciation that scientists in the 1800s noticed was our most recent one. ... The tilt affects where the globe is receiving the most solar radiation. Millions of Years Ago, the Poles Moved — And It Could Have ... https://www.discovermagazine.com › environment › mi... Nov 26, 2018 — By looking at multiple hotspots across the globe, they can quantify ... In black, the extent of the glaciers during the last Ice Age. The Ice Age | Answers in Genesis https://answersingenesis.org › ice-age › the-ice-age-cause Feb 17, 2011 — From a uniformitarian perspective, the earth has experienced many ice ages. Some were so extensive that they almost covered the entire globe in ... Ice Age Extinctions: What Happened? https://www.moas.org › Ice-Age-Extinctions--What-Ha... Jan 23, 2020 — Animals must be affected over the entire globe not just regionally. Second, an extinction event must happen very quickly in a short geologic ... Solar Radiation as a Cause of Ice Ages - Nature https://www.nature.com › news The striking advances of great ice sheets over large areas of the globe which have occurred at long geological intervals have attracted a great deal of ... Snowball Earth - an overview | ScienceDirect Topics https://www.sciencedirect.com › topics › snowball-earth In between each major ice age, the planet is believed to have been ... A gradual cooling and drying of the globe started some 50 million years ago. Ice age - New World Encyclopedia https://www.newworldencyclopedia.org › entry › ice_age Within a long-term ice age, individual pulses of extra cold climate are ... in which permanent ice covered the entire globe and was ended by the effects of ... Ice core basics - Antarctic Glaciers https://www.antarcticglaciers.org › glaciers-and-climate The presence of a “Little Ice Age”, a cooler period ending ~100 to 150 years ago ... You are correct that CO2 would be the same around the globe, as it is a ... Carbon dioxide helped end last ice age: U.S. researchers https://www.reuters.com › article › carbon-dioxide-help... Apr 4, 2012 — That slight sun-ward tilt melted those northern ice sheets within a few hundred years, pushing global sea levels up by about 33 feet, or by more ... An ice age lasting 115000 years in two minutes - ETH Zürich https://ethz.ch › eth-news › news › 2018/11 › an-ice-ag... Nov 6, 2018 — Around 115,000 years ago, the last glacial period in the earth's history began. It was an eventful time, as glaciers advanced from the Alps onto ... The ice age that never was | New Scientist https://www.newscientist.com › article › mg19926721-... Sep 3, 2008 — Could a few primitive farmers really have changed the climate of the entire globe? If you find this hard to believe, you're not the only one. james-croll-1821-1890-ice-ice-ages-and-the-antarctic ... https://www.cambridge.org › services › content › view › j... by DE Sugden · 2014 · Cited by 14 — Later Croll developed the theory further by showing how longer-term variations in obliquity, or the tilt of the. Earth's axis, are also involved (Croll 1875, ... Finding the Missing Ice Age | BU Today | Boston University https://www.bu.edu › articles › finding-the-missing-ice-... Raymo studies these shells to better understand the ice ages that have ... scientists drill cores deep in the ocean floor at sites around the globe and take ... Scientists know that irregularities in the Earth’s orbit, which occur every 23,000, 41,000, and 100,000 years, affect global climate cycles. Those deviations can nudge the northern hemisphere farther from the sun, causing ice to remain through the summer and auguring a new ice age, like the one that ended 10,000 years ago in North America. But starting in the late Pliocene era, some three million years ago, evidence of the 23,000-year cycle of climate change disappeared from the climate record. That brings us back to those tiny ocean dwellers, any of the 40 species of foraminifera, or forams, single-celled organisms with calcium carbonate shells. When forams die, their shells fall to the bottom of the ocean. Over millions of years, these deposits have become part of the ocean floor, and they happen to be an excellent indicator of the ocean’s temperature at the time of their demise. “Oxygen has two stable isotopes, oxygen-16 and oxygen-18, the ratio of which in the ocean is controlled by the amount of ice on land,” Raymo explains. “When ice sheets grow on land, water evaporates off the ocean, and the oxygen-16 molecule, because it’s lighter, evaporates at a greater rate.” Thus, when ocean sediment strata are heavy with oxygen-18, it’s a sign that there is more ice on land. “The whole ocean was relatively enriched in the heavy isotope of oxygen 20,000 years ago, and we know independently from fossil coral reefs that the sea level was 130 meters lower,” says Raymo. “All that water was in an ice sheet, and we can see the evidence for ice on land.” To analyze the oxygen content of ancient ocean water, scientists drill cores deep in the ocean floor at sites around the globe and take long tubes of the sediment — which includes the forams, whose calcite shells reflect the oxygen content — back to the lab. Fossils extracted from the cores are dissolved in acid and tested. Based on what she found in the sedimentary record, Raymo theorized in a Science paper last year that from one million to three million years ago, a significant change in ice volume was taking place in Antarctica, much more so than conventional wisdom holds, as the tilt and rotation axis of the Earth changed. She proposed that Antarctic ice sheets were melting while ice was forming in the northern hemisphere, canceling the effect of the 23,000-year cycle in the ocean water record as the light and heavy isotopes of oxygen mixed. If her hypothesis is true, the ice sheet covering North America “should be waxing and waning with both 41,000- and 23,000-year periodicity, not just the 41,000-year period inferred from the oxygen isotopic record of seawater,” Raymo says. To test this idea, she’s examining samples from cores drilled more than 20 years ago just off the mouth of the Mississippi River. Initial results show water with lighter oxygen isotopes at the predicted intervals, says Raymo. Her theory, which she is writing about in an upcoming issue of Nature, is garnering interest in the paleoclimatology community. https://www.bu.edu/articles/2008/finding-the-missing-ice-age/ Are we heading into a new Ice Age? - Skeptical Science https://skepticalscience.com › argument Without human interference, the Earth's orbit and tilt, a slight decline in solar output since the 1950s and volcanic activity would have led to global cooling. Milankovitch Cycles - Australian Earth Science Education https://ausearthed.blogspot.com › 2021/02 › milankovit... Feb 25, 2021 — Obliquity: Earth's axis of rotation is tilted as it goes around the Sun. ... Milankovitch calculated that ice ages would occur every 41 000 ... Exam III http://courses.geo.utexas.edu › LABS › ExamIV During a period when the earth's orbital tilt is at a minimum, ... a. a Medieval Warm Period, a cold Little Ice Age, and a warming trend since the late 19th ... Ice age theory | SpringerLink https://link.springer.com › ... Ice ages have occurred from time to time through geologic history but occupy ... of the globe and in rocks of various ages Schwarzbach, 1974; Frakes, 1979). Scientists May Have Solved Mystery Behind Extinction of Ice ... https://www.newsweek.com › ... › Extinction Apr 18, 2017 — Updated | The extinction of megafauna across the globe at the end of the last Ice Age appears to have been driven, in part, by moisture from ... Forcing and Feedback - American Chemical Society https://www.acs.org › acs › atmosphericwarming › forci... The end of a glacial period (ice age) and onset of an interglacial, coincides with the times when the northern hemisphere tilts toward sun at high obliquity ... What would happen if the Moon disappeared? https://www.rmg.co.uk › stories › topics › what-would-... It would move from no tilt (which means no seasons) to a large tilt (which means extreme weather and even ice ages). OM-43936-1_Misty Winter Moon © Rob Mogford. https://geocraft.com › WVFossils › ice_ages by SC Change · Cited by 6 — Since the end of the Ice Age, Earth's temperature has risen approximately 16 ... 41,000 year cycle: Cycle of the +/- 1.5° wobble in Earth's orbit ( tilt ) ... Global Warming:A Chilling Perspective - Geocraft.com https://geocraft.com › WVFossils › ice_ages by SC Change · Cited by 6 — Since the end of the Ice Age, Earth's temperature has risen approximately 16 ... 41,000 year cycle: Cycle of the +/- 1.5° wobble in Earth's orbit ( tilt ) ... Administration Proposals on Climate Change and Energy ... https://books.google.com › books United States. Congress. House. Committee on Transportation and Infrastructure · 2007 · ‎Climatic changes The ocean expands , tilts , globe tilts , and then something happens , conveyor belt shuts down , and we have an Ice Age . Just the opposite of what people ... History of Washington County, Iowa: From the First White ... https://books.google.com › books Howard A. Burrell · 1909 · ‎Washington County (Iowa) And not only that , but the offices of glacial ice had to be invoked to ... as , in alternating hot epochs , when the tilt of the globe's axis gave the ... Science and Invention - Volume 9 - Page 910 - Google Books Result https://books.google.com › books 1921 · ‎Science It would follow that ecliptic and consequently in the tilt of days and ... MAXIMUM TILT GLACIAL PERIOD CENTER OF EARTH'S ORBIT SUN , ICE CAP ICE CAP THE ... Mines and Methods - Volume 2 - Page 43 - Google Books Result https://books.google.com › books 1910 CAUSE OF CLIMATIC VARIATIONS THE GLACIAL PERIOD AND THE EFFECT IT IS ... the globe may have had more of a tilt than it now has , or that the north pole may ... Richard Brautigan S Trout Fishing In America The P https://cannes.propmark.com.br › viewcontent Oct 29, 2015 — will guide you to understand even more regarding the globe, experience, some ... California, at the age of forty-nine. The physics and chemistry of the formation, absorption ... https://jummor.pics › article › the-physics-and-chemistr... Nov 7, 2022 — ... lockdowns went into effect virtually across the globe. ... the slow increase in surface temperatures since the end of the last Ice Age. https://www.mainepublic.org/environment-and-outdoors/2022-12-12/a-fish-thats-swum-in-maine-ponds-since-the-ice-age-faces-an-uncertain-future 

 

https://urbanmatter.com/chicago/journey-to-the-polar-bear-capital-of-the-world-in-canada/https://urbanmatter.com/chicago/journey-to-the-polar-bear-capital-of-the-world-in-canada/''

 

Science
Oldest British DNA reveals mass immigrations after last ice age
Both caves date to the Paleolithic, a turbulent time that followed the end of the last
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Dinosaurs took over amid ice, not warmth, says a new study of ancient mass extinction

Thriving in a series of sudden global chills that killed competitors

Date:
July 1, 2022
Source:
Columbia Climate School
Summary:
There is new evidence that ancient high latitudes, to which early dinosaurs were largely relegated, regularly froze over, and that the creatures adapted -- an apparent key to their later dominance. 
https://www.sciencedaily.com/releases/2022/07/220701143118.htm
 
 
and a 700,000-year-old horse bone that yielded what was then the oldest genome ever sequenced.
https://www.smithsonianmag.com/history/well-preserved-30000-year-old-baby-woolly-mammoth-emerges-from-yukon-permafrost-180980388/
 
 https://economictimes.indiatimes.com/news/international/us/global-warming-scientists-suggest-controversial-plan-to-re-freeze-earths-poles-details-here/articleshow/94267579.cms


https://www.bostonglobe.com/2022/09/11/business/organ-transplant-startup-thinks-inside-box/
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Study: A plunge in incoming sunlight may have triggered “Snowball Earths”

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https://news.mit.edu/2020/sunlight-triggered-snowball-earths-ice-ages-0729



Cool Finds

Well-Preserved, 30,000-Year-Old Baby Woolly Mammoth Emerges From Yukon Permafrost

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The 1970s Ice Age Myth and Time Magazine Covers - by David Kirtley

https://scienceblogs.com/gregladen/2013/06/04/the-1970s-ice-age-myth-and-time-magazine-covers-by-david-kirtley

 https://www.bostonglobe.com/2022/02/14/business/keurig-ice-cream-is-heating-up-fast/

Would Nuclear Winter Cancel Out Global Warming?

 https://hackaday.com/2022/01/25/would-nuclear-winter-cancel-out-global-warming/

 

Newsweek
Evidence Upholds Snowball Earth Theory That Our Planet Rapidly
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described as a period where Earth experiences far lower...

 

WIRED
The World Was Cooler in 2021 Than 2020. That’s Not Good News
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