Name: Is an Ice Age Coming? | Space Time | PBS Digital Studios
Uploaded: 2018-02-05T06:48:38.000Z
Duration: 15 min 28 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Earth's climate shifts
between short periods

of warm and long, long
periods of frigid cold.

to think that the current warm
period might be nearly done.

Is the Ice Age coming back,
or will human activity

swing us wildly in the
opposite direction?

and is characterized by a
massive glaciation-- vast ice

all the way down to the Missouri
River through Siberia, much

of Europe, and spreading out
from all major mountain ranges.

Right now, we're in a
brief interglacial phase--

These interglacial
periods are short lived.

The Quaternary Ice Age has
lasted 2.5 million years

It's 10,000 to 15,000-year
warm patches are separated

by glacial periods that last
several times as long as.

The current respite is
called the Holocene era,

Temperatures rose, glaciers, and
woolly mammoths migrated north,

saw the rise of agriculture,
writing, cities,

All of our recorded, even
our remembered history,

that these relatively
summery millennia are

The current interglacial
is already long.

Does this mean that the
glaciers are overdue?

to understand what triggers
the march of the glaciers

In fact, we know the
broad answer to this,

Earth's motion around the
sun changes, and with it,

the intensity and
distribution of sunlight.

It was Serbian scientist
Milutin Milankovitch

who realized that the
gravitational tug of Jupiter

and Saturn would lead to
three periodic shifts that

might explain the
enormous climatic swings

of Earth's elliptical orbit
shifts from almost completely

circular to somewhat more
elliptical in 100,000-years

Earth's most distant
point from the sun--

One hemisphere will experience
summer at Aphelion and winter

at Perihelion and milder
seasons all around.

The Southern Hemisphere is
closer to the sun in summer

and further in the winter,
so more extreme seasons.

However, the difference
in sunlight intensity

due to this difference
in distance from the sun

Two, the pointing of
Earth's axis precesses.

It rotates 360 degrees over
approximately 26,000 years.

In addition, the long axis
of Earth's elliptical orbit

Together, these two effects
define where in the orbit

They combine to produce a
21,000-year cycle called

So eventually, the north's
mild Perihelion winter

Our spin axis is now tilted
at 23 1/2 degrees relative

This obliquity oscillates
between 22.1 and 24.5 degrees

High obliquity means
more extreme seasons.

But it's low obliquity that
ultimately leads to a colder

Because then the highest
latitudes, where glaciation

Now, Milankovitch
predicted that obliquity

would drive climate
variations, because it governs

We can reconstruct our
planet's climate history

The most famous is the nearly
four-kilometer-deep hole

drilled in the Vostok
Glacier in Antarctica.

This glacier was built up
by millennia of snowfall.