Ocean acidification| Global Change| AP Environmental science| Khan Academy

- [Instructor] In this video,

we're going to talk a little
bit about ocean acidification.

And as we'll see,

it's all related to increased
carbon dioxide concentrations

in the atmosphere.

And we have talked about
this in other videos,

but we can see if we look at
carbon dioxide concentrations

over the last 800,000 years,

which is well before modern
human beings existed,

it has oscillated between
roughly 200 parts per million

and 300 parts per million.

But then if we look at modern times,

the spike has gone well beyond that range.

And this axis right over here,
it's covering so much time.

It might not be obvious when
or why the spike has happened.

So let's zoom in a little bit

on the last several hundred years or so.

And when you do that,

this graph is showing us two things.

In blue, we're seeing the actual emissions

of carbon dioxide.

And if we go pre-industrial revolution,

or the early stages of
the industrial revolution,

our emissions of carbon
dioxide were very low

and fairly flat,

and we have seen that they
have gone up dramatically,

especially over the last 100 or so years.

And that carbon dioxide

doesn't just immediately
leave the atmosphere.

It stays in the atmosphere for a while.

So as we increase our emissions,

the cumulative concentration
of carbon dioxide has gone up

to those levels that we just saw.

Before the industrial
revolution, or the early stages,

we were within that range

that we saw over the last 800,000 years,

but then it cumulatively has increased

so to get us to this place
that is far out of that range.

And to appreciate what
it's doing to our oceans,

we just have to recognize that
the carbon dioxide in the air

is in interaction with the ocean,

actually with water everywhere.

So if I were to have some H2O, or water,

in reaction with carbon dioxide,

that is going to react, or
it could be in equilibrium,

to form what is known as
carbonic acid, which is H2CO3.

If you wanna know how
the bonds are structured,

it looks like this,

where each of the oxygens
are attached to a hydrogen.

And the reason why this
is called carbonic acid,

is because it can easily
release a hydrogen ion.

So this can be in
equilibrium with bicarbonate,

which is HCO3 minus.

So it's really just our carbonic
acid minus a hydrogen ion,

plus a hydrogen ion.

So as you have more
carbon dioxide in the air

that reacts with water in the ocean,

well, then you're going
to have more carbonic acid

and you're going to have
more of your hydrogen ions.

The reaction is going to go this way

as you have more of this stuff,

and especially more of the carbon dioxide.

And we have observed that
in the oceans themselves.

We have seen that ocean pH,

if we go to the early
industrial revolution,

it was around 8.2 and it has gone to 8.1.

And you might recognize
that the lower the pH,

the more acidic it is, but
you also might be saying,

"Hey, that doesn't look
like that much of a change,"

but it actually turns
out that pH is measured

on a logarithmic scale,

so we're actually talking
about powers of 10.

So this change, if you really
wanna get into the math,

pH is the negative log of the
hydrogen ion concentration,

and so the hydrogen ion concentration

here relative to there,
if we wanted to compare,

if we wanted see how much it grew,

you would say 10 to the
negative 8.1 over 10

to the negative 8.2.

And if you look at this analysis,

you'll see that this
is approximately 1.26,

or another way of thinking about it,

over the course of the
industrial revolution,

because of the trends we
have seen in this graph

that our oceans are about 26% more acidic.

And to appreciate why this is a big deal,

I will remind you that
things like coral reefs

or shells in sea animals,

these are formed with calcium carbonate.

In calcium carbonate,

you have a positively charged
calcium ion forming ionic bond

with a carbonate ion, and
carbonate looks like this,

which looks a awful lot of
what we see right over here

in the carbonic acid, or the bicarbonate.

And so if all of a sudden
you have a lot more

of these hydrogen ions in
the water and dissolved,

everything's more acidic now,

it might disrupt this
process of formation.

Some of this carbonate might go

and nab some of these hydrogen ions,

less likely to form an
ionic bond with the calcium.

It also doesn't just
directly affect things

like calcium carbonate,
which is everywhere,

it's actually the main
constituent of pearls.

It's the structure of so many,

especially rigid structures
in life, including sea life,

it's actually also antacid.

TUMS is mainly calcium carbonate,

but this acidity in general

is going to throw all
sorts of organisms off

of their homeostasis.

Organisms are highly, highly
sensitive to changes in pH,

to changes in acidity.

But the big picture takeaway,

a lot of talk is about global warming

and carbon dioxide
concentrations in the air,

but it's also not only warming the ocean

because of the greenhouse effect,

but it's also making
the oceans more acidic,

which is having some
obvious consequences now,

and probably some follow on consequences

that we are just beginning to understand.