This lecture is going to be a bit different from normal. I'm going to do a
video demo with this super-awesome simulation of climate change from Phet
at the University of Colorado and then once I've given you a visual of what I'm
talking about I'm going to move back into the normal lecture slides. So to
talk about climate change, we need to start by talking about different gases
that exist in the atmosphere, and an important difference between different
types of gases in the atmosphere. So what I have here is a photon gun that's going
to fire little photons (little particles of light) at each type of atmospheric
gas so this is a molecule of atmospheric gas. This is specifically ch4,
which has the more common name of methane. I'm going to turn this on and
notice a pattern in how this molecule reacts to the photons that are impacting
it. so you can see photons are coming out
and you'll notice that as the photons go through the molecule, some of the photons
just passed right by the molecule, but some of the other photons are absorbed
by the molecule and shot off in a random direction. So this is an extremely
important pattern. These are infrared photons. That means that they're photons
with wavelengths that are too long for us to see. You'll notice that when I
shoot visible light at this molecule nothing happened, so visible light can
move through this molecule very easily, but infrared photons cannot.
So because visible light can move through, that actually means that this
gas is mostly invisible to us, which makes sense because this is one of the
gases in the atmosphere in the air. And because we can't really see the
molecules that make up the air, it makes sense that visible light can move
through it, but infrared light like that we can't see cannot always move through
it. Okay, I'm now going to compare methane with an oxygen molecule O2.
So you'll notice that now all the infrared photons are passing right
through the oxygen molecule, and not being absorbed and bounced out by the
molecule, so the infrared photons just keep moving along in whatever direction
they already happen to have. I'm now going to go over to a CO2
molecule (you know that better as carbon dioxide) and you'll notice that unlike
the oxygen and like the methane, the carbon dioxide molecule is absorbing
infrared photons and causing them to bounce off in random direction. It's not
doing that for every photon, but for a lot of the photons it's taking the
photons in and then bouncing them back in a different direction. Next on our
list of things to test is H2O which you know better as water.
And you'll see here that the water molecule is actually also absorbing and
bouncing back infrared photons. So just like methane and carbon dioxide, water is
also taking some of that energy in and bouncing it back in a random direction.
Last thing to test is nitrogen.
Nitrogen is the most common gas in our atmosphere and you'll see that nitrogen
is also allowing photons to just pass right through without bouncing them back
in random directions. So what we found so far is that methane, carbon dioxide, and
water are all types of gases that absorb some infrared photons and bounce them
back in random directions, and nitrogen and oxygen do not absorb infrared
photons and do not bounce them back in random directions. If I click this button
that says build an atmosphere right here, I can choose how many of each type of
molecule I have present in my atmosphere. So I'm gonna make an atmosphere out of
just nitrogen and oxygen molecules and then turn on this little ray. You'll
notice that it's now shooting a lot more infrared photons and the photons are
just moving straight through my atmosphere. None of them are being
bounced back in any way. however if I include these other gases
like methane or CO2 or H2O you'll notice that some of them are absorbing the
photons and bouncing them back in random directions, and the more of these I
include the more photons get randomly absorbed and bounced back in a random
direction. So now that you can see the difference between molecules that absorb
infrared photons and molecules that don't. I can give you the formal
definition of the difference between those things. So a molecule that absorbs
infrared photons we call a greenhouse gas.
The reason why we call it a
greenhouse gas will be explained in just a moment, but for now you need to know
that if it absorbs photons and bounces them back in random directions it's a
greenhouse gas, and if it doesn't absorb photons and just lets them pass right
through it it is not a greenhouse gas. So there's a simple reason why we call
these things greenhouse gases. It's because when we observe how they behave
in the atmosphere as a whole they behave a lot like glass panes of a greenhouse
roof. So greenhouses are glass buildings that are designed to keep plants inside
and keep them warm, so if you're trying to grow plants and you don't have a
greenhouse, what happens is that visible light from the sun is sent down from the
sun to earth, and the earth rebounds a lot of that visible light as infrared
photons that go back up into space carrying some energy with them, and if
you don't have any kind of layers of your greenhouse to keep your plants safe
all that energy is kind of lost. It just goes straight into space. But if I add a
glass layer for this greenhouse you'll notice that some of the photons get
bounced back and stay inside of the area that I've glassed off.
And if I add more glass plates more of those photons are kept from going off
into space, so just like those glass layers of an actual greenhouse,
greenhouse gases behave in a similar way. What they do is as visible light comes
down from the sun and bounces back up, they trap some of the infrared light
that's being bounced back up by absorbing them and shooting them off in
random direction. So just like we saw over here in the photon absorption
simulation over here those greenhouse gases are now present everywhere in this
atmosphere and they're going to randomly bounce some infrared photons back
towards the earth so when I hit play on the simulation
I'm keeping the greenhouse gas levels as they are today. So you'll notice that
some of the photons are being bounced back into the atmosphere while others
are leaving back into space like this, and having some greenhouse gases in the
atmosphere is extremely important because if I set it so that there are no
greenhouse gases in this atmosphere you can see that all of the infrared photons
are bouncing back up into space, which means that the earth is not able to
store any heat energy inside of it, and so the temperature plummets way below
what we're used to over here so you can see it dropped very quickly. So some
greenhouse gases are definitely very good and the amount of greenhouse gases
in the atmosphere determines how much energy is in the atmosphere. So I'm gonna
set this up to where the greenhouse gases were at 1750. So you can see that
this is how much of each type of greenhouse gas was in the atmosphere in
the year 1750. And what's happening here is that some
of the energy, some of the photons from the sun, are being bounced back into the
atmosphere instead of going up into space, and the law of conservation of
energy says that energy has to go somewhere. You have to always account for
it. So energy is never going to just disappear from the atmosphere or from
Earth's system. It has to go somewhere, it can be shot back out into space like
some of these red photons up here or it's gonna stay in the atmosphere
bouncing around as a photon, which can turn into thermal energy, so the amount
of greenhouse gases in the atmosphere determines how much energy the Earth's
atmosphere can store at a time, which basically determines the temperature of
the earth. So the greenhouse effect is a really straightforward mechanism. Just
because there are a bunch of greenhouse gases in this atmosphere absorbing and
shooting off these red photons in random directions that's keeping some of the
energy in the atmosphere of the earth. So that's causing the Earth's climate to
stay at a particular temperature. So you'll notice over here the CO2
specifically in the atmosphere is 280 parts per million. That means that if you
were to take a chunk of the atmosphere, 280 millionths of that atmosphere would
be made up of carbon dioxide specifically, and this is in 1750 and the
significance of 1750 is that it's a year before the Industrial Revolution, before
humans really started to put out large emissions of carbon dioxide to the point
where the amount of carbon dioxide in the atmosphere actually changed. So just
to give you a demonstration of how much the carbon dioxide
has changed and is changing from 1750 to today (and by today it doesn't actually
literally mean today, it means when the simulation was created) you can see that
after the Industrial Revolution we've jumped up to three hundred and
eighty-eight parts per million of carbon, and it's a little difficult to see but a
few more of these infrared photons are being bounced back and prevented from
going into space and just a little bit more carbon causing a little bit more
photons to be bounced back into the atmosphere has just a little effect on
the temperature. It can raise it by just a few degrees so the adjustment from 280
parts per million where the average temperature is 57 degrees to today at
388 parts per million when it's about sixty degrees has an effect. What's
especially scary about the simulation to me is that this 388 parts per million is
already very very inaccurate. Just because the simulation is a few years
old, the actual amount of carbon in the air as of me recording this video in
2019 is actually 410 parts per million. So just since the simulation was
published a few years ago the total parts per million has already risen from
388 all the way up to 410 which is a pretty huge abrupt shift, and the reason
why we're worried about this is that if we continue to increase the amount of
greenhouse gases in the air eventually more and more photons will be trapped by
the atmosphere causing more and more energy to be trapped in the atmosphere,
because again energy cannot be created or destroyed, it always has to go
somewhere. This will cause the earth's temperature to continue to advance up
and up and up like this, so this is why climate scientists universally believe
that greenhouse gases in particular are the main cause of climate change, and the
human addition of more greenhouse gases into the atmosphere is mainly what is
changing the climate. What's especially concerning is that the agreed-upon
dangerous point where global climate change starts to get dangerous is
actually at 350 parts per million, so not only were we past that when the
simulation was created, but we've also gone significantly far beyond that into
410 parts per million since the simulation was
created. So the emission of these greenhouse gases is a main concern in
power production. It's probably the main thing that's considered now when new
power stations are built, so it's going to be a main focus of this unit as well.
Going back into the lecture slides, this is the official definition of greenhouse
gases. It's any gas that absorbs and emits radiant energy from the Sun. We
call these greenhouse gases because they store energy in the Earth's atmosphere
like the roof of a greenhouse, and if we significantly change the amount of
greenhouse gases in the atmosphere we will change the energy in the atmosphere,
and this causes climate change. And water vapor, carbon dioxide, methane, and nitrous
oxide are the four most common greenhouse gases in the atmosphere in
order of how common they are. And a significant change in the amount of
these greenhouse gases is what causes climate change, which is a change in the
overall average temperature of a region or of Earth. It's caused by a change in
the greenhouse gas makeup of the atmosphere. Some people get a little
confused by that definition and assume that it can mean anytime weather is
changing at all, but it actually means a change in the overall average
temperature of the region. So right now as an example in Virginia it drops to a
certain temperature in the winter and rises to a certain temperature in the
summer, but those by themselves are not examples of climate change. A change in
climate would be like if the overall pattern throughout the year of Virginia
changed to what the pattern in somewhere like Arizona is like, where the
temperatures at specific times of the year are very different from what they
are here, so scientists and everyday people and politicians are all very
concerned about climate change because it threatens how and where food can be
grown and where people can live, and if climate change gets especially bad it
could actually spiral out of control to the point where humans can no longer
survive on earth. There are very different models of what will happen
with climate change and there's no certainty about exactly what will happen,
but there's enough of a risk of very extreme bad things happening that people
are concerned, and so most of the decisions people make about how to
generate power now take climate change into consideration, and so we're going to
do that as well in this unit on power. And the IB test also includes questions
about climate change along with the rest of the
power unit when you're testing on that subject. I'm going to leave a few links
in the description if you're interested in looking at this more. The first link
I'll put is the link to that PhET simulation I was using at the beginning.
I also include a video in the description about the specific effects
and concerns about climate change, and those effects aren't being tested on in
this unit but they're still very important to know about.