The crazy prediction of a new Ice Age Coming: Milankovitch Cycles
On Christmas day, while people in Italy drink hot chocolate under their blankets,
Brazilians are at the beach drinking some iced beverages.
All of this could however change in the future. Imagine a world where the snow never stops
falling, the cold never fades, and survival becomes a daily struggle.
If a long winter period strikes the Earth, we would find ourselves in a post-apocalyptic state.
Resource scarcity would be the first issue to hit us. The ground would freeze solid,
crops would perish, and food would become scarce. To survive, we would need to choose between
hoarding and sharing. Those who choose to hoard would become isolated and eventually come to ruin.
Scientists think we might find ourselves in this situation in the years to come.
There are cycles on Earth that are in conflict: periods of hot weather alternate with cold ones.
However, these conflicts won’t last forever: in the future, the conflict
will eventually stop, and a long winter will come. But how do these cycles work? Join me to get to
know more about it! ---
Surrounded by Cycles Let’s start by saying that, here on Earth, we are
basically surrounded by cycles. Let me explain. Our lives literally revolve around them: a series
of events that are repeated regularly in the same order. There are hundreds of different types of
cycles in our world and in the universe. Some are natural, such as the change of the seasons,
annual animal migrations, or the circadian rhythms that govern our sleep patterns. Others
are human-produced, like growing and harvesting crops, musical rhythms, or economic cycles.
Every year, on the 25th of December, the world celebrates Christmas Day.
In the collective imagination, Christmas is made of snow and hot chocolates.
This day is associated with snow and Santa riding his reindeer,
bringing gifts and joy to all people, whether they’re kids or adults.
However, if you live in Brazil, you will probably notice one thing:
Christmas Day falls during summer. Many people like to go to the beach
to tan! For the Brazilian people, there’s no hot chocolate on Christmas: it would be crazy to even
think about making one! You might want to eat an ice cream instead. The one and only reason why
this happens is because of…seasons. ---
The Cycle of Seasons You might already know why we have seasons,
but I think it’s worth reviewing, as this will serve as a starting point to understand the main
topic of this video, the Milankovitch Cycles. The reason why we have seasons is due to the
revolution of Earth around the Sun and the inclined axis. As our planet orbits the Sun,
the tilt of its axis causes different parts of the world to receive varying amounts of sunlight. This
results in the changing of seasons in different parts of the world at different times of the year.
During summer, the hemisphere that is tilted towards the Sun receives more direct sunlight,
resulting in longer days and warmer temperatures. Conversely, the hemisphere that is tilted away
from the Sun experiences shorter days and cooler temperatures. This contrasting pattern is reversed
during winter when the hemisphere tilted away from the Sun receives less direct sunlight,
resulting in shorter days and cooler temperatures. Spring and fall are the transition seasons between
summer and winter, and they occur when the Earth's axis is neither tilted toward nor away
from the Sun. During these seasons, the amount of sunlight received is more evenly distributed
across the Earth, resulting in moderate temperatures and more balanced weather patterns.
Seasons have a significant impact on life on Earth. Plants and animals have adapted
to the changing climate, using cues such as temperature and day length to regulate
their life cycles. Many animals migrate to warmer climates during the winter months, and
some plants only flower during certain seasons. In addition to its impact on the natural world,
seasons also affect human activities. Seasonal changes can influence everything from our moods
and behavior to the economy. For example, winter sports and activities are popular in places where
it snows, while beach activities are more prevalent in places with warmer climates.
As you can see, seasons are an important cycle that repeats regularly, with each season bringing
new growth and changes to the natural world. All over the course of one year, periods of warm
weather alternate to colder ones. ---
The Milankovitch Cycles So, the presence of seasons is due to
the particular configuration of a planet’s axial tilt with respect to its orbiting plane around
the host star. But, as the Serbian scientist Milutin Milankovitch pointed out a century ago,
this is not the only factor capable of having an impact on the Earth’s weather and climate.
This genius hypothesized that the long-term, collective effects of changes in Earth’s
position relative to the Sun are a strong driver of Earth’s long-term climate,
and are responsible for triggering the beginning and end of glaciation periods (Ice Ages).
Did I already mention this guy was a genius? He knew very well that the orbit of a planet
is described by what aerospace engineers call the “orbital elements”. These are six important
quantities that help describe the movement of an object around another object, whether it is an
artificial satellite like JWST around the Earth or a star around the black hole at the center
of our galaxy. He first asked himself what would happen to the Earth if one of these elements, the
so-called eccentricity, slowly changed over time. ---
Changes in Eccentricity The eccentricity gives
information about the shape of an orbit. When it is zero, the orbit is a circle.
The more you depart from zero, the more stretched and elliptic your orbit is.
The thing is, due to the gravitational perturbations of Saturn and Jupiter, and other
minor factors, the Earth’s eccentricity, which is quite low, can vary over time, changing the shape
of the Earth’s orbit around the Sun. This, in turn, affects the distance between the two bodies.
Eccentricity is the reason why our seasons are slightly different lengths, with summers in
the Northern Hemisphere currently about 4.5 days longer than winters, and springs about three days
longer than autumns. As eccentricity decreases, the length of our seasons gradually evens out.
What Milankovitch did was to examine how these variations affect how much solar radiation
reaches the top of Earth’s atmosphere, as well as WHERE this radiation reaches.
He found out that, when the Earth’s orbit is at its most elliptic, about 23 percent more incoming
solar radiation reaches Earth at our planet’s closest approach to the Sun each year than does
at its farthest departure from the Sun. Currently, Earth’s eccentricity is near its least elliptic
(most circular) and is very slowly decreasing, in a cycle that spans about 100 thousand years.
However, the change in global annual insolation due to the eccentricity cycle is very small.
Because variations in Earth’s eccentricity are fairly small, they’re a relatively minor factor
in annual seasonal climate variations. ---
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Changes in Obliquity But that’s not the end of it!
This genius…uhm…Milankovitch also took into account something else:
the obliquity and the axial precession.
The obliquity is the angle between the plane of the Earth's orbit and that of the Earth's equator.
This tilt has varied between 22.1 and 24.5 degrees over the last million years. The greater the tilt,
the more extreme our seasons are. Think scorching hot summers and bone-chilling winters.
Interestingly enough, a larger tilt angle actually leads to periods of deglaciation. So,
basically, more tilt equals more melting and retreat of glaciers and ice sheets.
But this effect isn't uniform worldwide. Higher latitudes experience a greater change in total
solar radiation than areas near the equator. Currently, Earth's axis is tilted about halfway
between its extremes at 23.4 degrees. And get this- that tilt angle is slowly decreasing in
a cycle that lasts about 41 thousand years. With his calculations, Milankovitch found out
that while our winters will gradually become warmer and our summers cooler, snow and ice
will begin to build up in high latitudes. This leads to large ice sheets reflecting
more of the Sun's energy back into space, which, you guessed it, promotes even further cooling.
--- Axial Precession
For what concerns axial precession let me first explain what it is.
I don’t know if you are aware of this, but the Earth wobbles slightly on its axis like
a spinning toy top. This wobble, caused by tidal forces from the Sun and Moon,
affects Earth's rotation and is known as axial precession. This cycle lasts about 27.7 thousand
years and makes seasonal differences more extreme in one hemisphere and less extreme in the other.
Currently, perihelion (Earth's closest point to the Sun) occurs during winter in the Northern
Hemisphere and summer in the Southern Hemisphere. But in about 13 thousand years, this will switch,
causing the Northern Hemisphere to experience more extreme solar radiation and the Southern
Hemisphere to have more moderate seasons. There's also apsidal precession, where Earth's
entire orbital ellipse wobbles due to interactions with Jupiter and Saturn. This cycle lasts about
112 thousand years and changes Earth's orbit's orientation relative to the elliptical plane.
Combined, axial and apsidal precession have an overall precession cycle lasting about 23
thousand years on average. And fun fact, Earth's North Star changes over time, with Polaris and
Polaris Australis being the current stars, but a few thousand years ago, it was Kochab and Pherkad.
--- Milankovitch’s Crazy Prediction
The small changes set in motion by Milankovitch cycles operate
separately and together to influence Earth’s climate over very long timespans, leading to
larger changes in our climate over tens of thousands to hundreds of thousands of years.
Still, what he found is both very interesting and scary:
at some point, we the Earth will eventually be experiencing another ice age.
The two main assumptions posed by Milankowitch were
1) that the changes in radiation at some latitudes and in some seasons are more important than others
2) that the obliquity is the most important of the three cycles for the climate.
Putting these into his own mathematical model, he calculated that Ice Ages occur approximately every
41,000 years. Given that the last ice age we know of happened roughly 20 thousand years ago,
this would in turn mean that the next ice age will be happening in 20 thousand years or so.
However, subsequent research confirmed that Ice Ages did occur at 41 thousand-year intervals
between one and three million years ago. But about 800 thousand years ago, the cycle of the Ice Ages
lengthened to 100 thousand years, matching Earth’s eccentricity cycle. While various theories have
been proposed to explain this transition, scientists do not yet have a clear answer.
This problem is also known as the “transition problem”.
In any case, according to the most recent astronomical measurements, there won’t be a new
ice age before 50 to 100 thousand years. ---
Predictions Accuracy Making predictions when it comes to
long-term climate on planet Earth is no picnic. In principle, a good estimate of the variations
of the orbital elements over time would make everything easy, if we only had a good model
linking these variations to climate variations. However, the orbital forcing mechanism that
acts on the climate is still not completely understood: Currently,
we lack a good model that expresses the climate changes in the function of the orbital ones.
Due to these reasons, research to better understand the mechanisms that cause changes in
Earth’s rotation and how specifically Milankovitch cycles combine to affect climate is still ongoing.
But the theory that they drive the timing of glacial-interglacial cycles is well accepted.
--- Hey! This video ends here! Thank
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