Name: 气候周期的历史（The History of Climate Cycles (and the Woolly Rhino) Explained）
Uploaded: 2021-05-03T08:14:58.000Z
Duration: 14 min 36 s
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700,000 years ago a rust-colored Rhino roamed the vast open Highlands of Siberia and Central Asia.

This ginger beast is better known as the Woolly Rhino and it made its living foraging in the cold dry Tundra steppes.

Siberia in the Pleistocene might sound cold to you, but it suited the woolly rhino just fine.

And 700,000 years ago the world was only a few degrees cooler than it is now,

which is why at the time the range of the woolly rhinos was restricted to the cold wilds of Siberia.

By about four hundred and fifty thousand years ago, global temperatures had dropped by about six degrees Celsius,

Glaciers crept out of their mountain ranges and down to lower elevations.

Tundra spread to other parts of Asia, and so did animals that were adapted to the cold,

including the woolly rhino, the mammoth, and the Saiga antelope.

After thousands of years of being confined to Asia, the woolly rhino

finally stepped foot into Europe, but that too didn't last long.

the climate warmed back up, and the Rhino and its Tundra were forced back into the highlands.

This whole cycle happened again and again,

which is why the Ice Age is more accurately known as the Ice Ages.

Over the rest of the Pleistocene epoch, the Rhino's range continued to grow and shrink in sync with global climate.

During warm periods, most of the rhino population retreated to cold places like Siberia,

but small populations found themselves stranded in places like the Pyrenees Mountains in Spain and France.

And then about 12,000 years ago, they finally went extinct.

So what caused the climate, and the range of the woolly rhino, to cycle back and forth between such extremes?

And what caused the woolly Rhino after so many years to go extinct?

More specifically, Earth's position in space, like where it is in its orbit around the Sun,

and what direction is that axis pointing?

These factors, and the way they change through time, have caused our climate to change a

And it's only been within the last century or so that we've begun to figure out that all of these factors change in cycles,

and those cycles can coincide or counteract each other which makes the history of our climate incredibly complex.

But when you put all of the pieces of the climate puzzle in front of you, you can start to understand some

chapters of our deep past, like the fate of the woolly rhino.

We've known that the Ice Ages happened for a pretty long time.

But what actually caused them was largely unknown until the early 1900s.

The man who solved the mystery was a Serbian mathematician and astronomer named Milutin Milankovic.

So today these cycles are known as the Milankovitch cycles.

Milankovic was obsessed with Ice Ages, both on our planet and on Mars, and he became

convinced that small changes in the angle of sunlight could be responsible for starting and ending those Ice Ages.

He already knew that parts of the earth that

received more direct sunlight from overhead are warmer,

like at the equator, which gives overhead sunlight year-round. And after years of study

Milankovic concluded that there were three main things that changed the angle of sunlight

in the northern and southern hemispheres.

The first and most important is axial tilt, also known as obliquity.

This is the angle at which Earth's axis leans either to or away from the Sun.

Milankovic thought that this had the biggest effect on climate because it has the most extreme influence on the angle of sunlight.

After all, the tilt of the earth is why we have seasons.

Right now the axis of our planet is tilted at about 23 and 1/2 degrees,

so for those of us who are further away from the equator

sunlight strikes the surface at a higher angle when our hemisphere is leaning towards the Sun,

And when we're leaning away from the Sun, sunlight strikes at a more shallow angle, like in the winter.

How exactly our earth got knocked over is still a bit of a debate,

but one popular theory is that earth collided about four-and-a-half billion years ago with a huge

planetary body that went on to form the moon.

And that impact sent us spinning like a top.

And just like a spinning top, the amount of earth's tilt changes, between about 22 and

24 degrees over the course of about 41,000 years.

Since a steeper tilt creates stronger extremes in temperature,

Milankovic was pretty sure that once someone figured out the precise timing of the ice ages,

they'd show that most major climate changes took place every forty-one thousand years.

But keep in mind our axis isn't just flipping back and forth.

It's also moving in a circle. Again, like that spinning top.

So in addition to the angle of its tilt, we also have to consider which

direction our axis is pointing at any given point in history.

This is known as axial precession or just axial wobble and our axis completes a full

circle about every twenty three thousand years.

And this affects the climate because it changes where in Earth's orbit each season happens,

because the Sun isn't in the exact center of Earth's orbit.

There are periods when we're closer to the Sun in our orbit, and periods when we're farther away.

Right now, based on the direction of Earth's axis, winter occurs in the northern hemisphere.

when Earth happens to be closest to the Sun in its orbit.

And summer occurs when it happens to be farther away.

But when precession is at the other end of the cycle and our axis is pointing in the opposite direction,

This creates more extreme seasons than the northern hemisphere has now.

Finally, the third part of the Milankovitch cycle is a feature known as eccentricity.

This is a change in the shape of Earth's orbit, from being roughly circular to being ever so slightly more eccentric or oval-shaped.

And earth's orbit changes from being more circular to less circular,

and then back again over the course of about a hundred thousand years.

But rather than changing the angle of sunlight,

the main effect of eccentricity is changing the lengths of the seasons.

A circular orbit creates seasons of equal lengths,

but slightly less circular orbit stretches out some seasons while compressing others.

So during periods with a highly eccentric orbit,

there may be long summers but also long winters.

In the end, his extensive calculations led Milankovic to conclude

that changes in the tilt of Earth's axis were the main factor that could cause enough cooling to make ice

As a result, he predicted that the most significant ice ages

would have happened every 41 thousand years or so,

If we look deep into the geological record,

we can see changes in climate that line up roughly with the cycle of earth's tilt,