Why is the world warming up?

(soft ambient music)

[Kristen] Why is the world warming up?

Let's think of Earth for just
a moment as a greenhouse.

Every second, a huge amount of energy

smashes into our greenhouse.

Our atmosphere, the glass roof and walls,

reflect some of that energy,

but most of it passes right
through and heats everything up.

Much of that heat used to
escape back into space,

keeping us at a stable, warm temperature.

But then something changed.

Humans began to spew enough carbon dioxide

to fill billions of greenhouses each day.

What does all that greenhouse gas do?

It makes the glass of
our greenhouse thicker.

Thicker glass means
heat escapes into space

much more slowly.

And don't forget, energy from the sun

is still streaming in
just as quickly as before.

The result is a planet with temperatures

too hot for our liking
and, eventually, living.