The Biggest Myth About Climate Change (2)
has gone the other way, up.
On longer time scales, the sun does sometimes
enter longer periods of lower-than-average
or higher-than-average brightness
that can affect warming or cooling over decades,
and while these have happened many times in human history,
we know this isn't happening now, because, again,
science people have been looking at the sun,
which, I must emphasize again, you should never ever do,
Moving past the sun, there is one violent factor
that can cause huge swings in Earth's energy balance,
volcanoes, and all their big hot gassy burps.
Now, besides lava, which we'll get to,
an erupting volcano releases lots of stuff
that can affect the amount of energy Earth holds on to
or sends off into space.
Now, when Vulcan, the god of fire,
gets all angry and sends one of his molten mountains
spewing into the atmosphere, not how it works,
along with that comes lots of ash and sulfur,
the ol' brimstone to go along with all that fire.
Both of these can increase the amount of solar radiation
that bounces back out into space,
either through seeding clouds,
which are basically bright sunlight reflectors,
or by directly reflecting that sunlight off
of tiny aerosols of ash or sulfur compounds.
Basically, volcanic ash and sulfur cause Earth
to bring in less energy than it loses,
so they're an overall cooling effect
that can last a couple decades.
But this is a pretty well understood climate process,
and volcanoes are erupting today at about the same rate
they have for most of the time humans have been
on this planet.
So we can't blame this warming
on some volcano drought or something.
But hoo, that's not the only effect volcanoes
can have on climate, dear friends.
No, no, we're just getting started with this lava-fest.
Erupting volcanoes and other big leaks of melty stuff
from inside the Earth, those also release enormous amounts
of carbon dioxide, a greenhouse gas.
That CO2 mostly comes from rocks that get recycled back
into melty stuff thanks to plate tectonics,
releasing their carbon into the magma
that eventually spews out during an eruption.
And eruptions can release a lot of CO2.
Like, this one time around 252 million years ago,
eruptions in modern-day Siberia covered
2 million square kilometers of land with lava,
and along the way set all the buried coal
in the area on fire, releasing just oodles of CO2
into the atmosphere, warming the planet enough
to kill more than 90% of life on Earth.
It was the largest mass extinction ever,
and it's all thanks to warming
caused by a 2 million square kilometer eruption.
So, yikes! Volcanoes can really get things hot and sweaty!
Thing is, that's not happening today.
Like, we know how many eruptions happen on Earth.
We can see them from space. We can measure them.
It's not like there's some secret pile of volcanoes
going off that nobody knows about.
There are memes that go around,
saying stuff like "In one eruption,
Italy's Mount Etna releases more than 10,000 times the CO2
that humans have in our entire existence,"
that's just not true.
Humans emit at least 60 times more carbon dioxide
than volcanoes do each year.
A big eruption might match human emissions for a few hours,
but they just don't last long enough or happen often enough
to rival us.
In fact, just a handful of U.S. states
emit more carbon dioxide in a year than all the volcanoes
on the planet combined do.
And besides, those large eruption events
that have massively thrown off Earth's energy budget
in those ancient before-the-dinosaurs times,
they happened over tens to hundreds of thousands of years.
Volcanic CO2 just can't explain modern warming.
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So, during all that talk of mass extinctions
and eruptions big enough to cover an entire country,
maybe you've been asking yourself
"Why isn't CO2 that high anymore?
What brought it back down?"
You're thinking. I like that.
Well, during the Great Dying, global CO2 levels
went up to at least 2000 parts per million.
I mean, compare that with our measly 415
or so parts per million today.
I mean, what, did plants eat it all?
No, plants didn't eat it all.
See, Earth has this cool trick
that keeps CO2 levels balanced in the atmosphere.
Thing is, like a sloth magician, it's a trick
that takes a really long time to pull off.
Now, kucky for you, I'm the kind of magician
who doesn't mind telling you how the trick works.
After an eruption, there's a bunch of fresh new rock
on the surface and a bunch of extra CO2 in the air.
Carbon in the atmosphere combines with water
to form a weak acid that falls to the surface in rain.
That acid dissolves those fresh new rocks
in a process called chemical weathering,
which releases ions that get washed into the ocean.
There, ions like calcium
combined with dissolved carbon dioxide
pulled from the air to form calcium carbonate,
which corals and plankton and other organisms
use to make their shells, until they die,
and then that calcium carbonate falls to the ocean floor,
eventually turning into limestone rock.
So if, say, you've got a bunch of volcanoes burping CO2
and lava out, give Earth several hundred thousand years
and all that carbon will get buried at the bottom
of the ocean again.
It's a pretty cool way of keeping things perfectly balanced,
as all things should be, as long as you're not in a hurry.
This slow magic trick is basically the invisible hand
that keeps Earth's natural thermostat from getting too hot.
But again, overall it cools Earth down,
so it too can't explain recent warming.
What about weird short-term climate cycles
with cool names like the El Nino-Southern Oscillation?
Maybe you read on Wikipedia,
they can mess with ocean temperatures and weather patterns
and all kinds of stuff.
Could that explain recent rapid climate change?
Well, a few decades ago it was, in fact,
hard to show that global warming caused by humans
was statistically significant over these natural cycles.
But we've blown way past those error bars,
and although scientists
still don't perfectly understand these cycles,
their magnitude is just too small
to explain the extreme heating we are seeing today.
And speaking of the oceans,
it's time we give them some credit
for saving our you-know-whats.
Because out of the 435 zettajoules of extra energy
that we've added to Earth's budget,
you remember, all those dynamite-filled Big Bens
we've been blowing up every second?
Well, 91% of that extra heat energy has been absorbed
by the oceans, which, don't get me wrong,
sucks for the oceans, but that big wet heat battery
has slowed down the heating of everything else.
If, for instance, all of that extra heat energy
oceans have absorbed on our behalf
were suddenly released into the atmosphere,
it would be more than 60 degrees hotter everywhere,
which is just insane and would lead to the extinction
of every living thing bigger than a microbe on this planet.
So thank you oceans. And we're sorry.
Other than an asteroid impact, or, I don't know,
photosynthesis evolving, there really isn't another process
in Earth's history that could have a major impact
on CO2 levels in the atmosphere or on Earth's energy budget,
in either direction.
But there is one process that's bigger than Earth
that we haven't talked about, wobbly orbits.
Since Earth's energy budget is influenced
by the amount and intensity of radiation energy
reaching Earth from the sun,
changes in Earth's position relative to the sun
can have major effects on Earth's long-term climate.
It's thought that slight tweaks to Earth's orbit
are responsible for triggering the beginning
and end of recent Ice Ages.
One of the major wobbles you should know about
is the shape of Earth's orbit, known as eccentricity.
Basically how circular or elliptical is our path
around the sun, as Earth gets gravitationally tugged on
by all those other planets that no one even lives on.
Right now, Earth is closest to the sun in early January,
and at its farthest in early July.
That means about 6.8% more incoming solar radiation
reaches Earth in January than in July.
But over the next 100,000 years or so,
the difference in solar radiation
between Earth's closest and farthest approaches
to the sun will be about 23%.
There's also the angle Earth's axis is tilted,
known as obliquity.
Now, while Earth's axis is currently around 23.5 degrees
off vertical, over the last million years,
it has varied between 22.1 and 24.5 degrees.
And since this tilt can affect how intense sunlight
is on a given area of Earth's surface,
this can affect Earth's overall climate,
especially the extent of ice at the poles.
Finally, there's the precession of Earth's axis,
kinda like how a spinning top turns as it turns.
Not only does this mean that, over time,
the north star won't be the north star anymore,
but also when combined with those other orbital wobbles,
it can exacerbate the difference
between winter and summer in each hemisphere.
Collectively, these orbital movements
are known as Milankovitch cycles, named in honor
of slightly off-kilter Hollywood actor John Milankovitch.
Wait.
I'm being told that they are in fact named
for Serbian scientist Milutin Milankovitch.
Depending on how the peaks and valleys
of the Milankovitch cycles line up, or don't,
they can change how much solar radiation
hits Earth's mid-latitudes by up to 25%.
That can take enough energy out of Earth's budget
to kick off long stretches of time
where Earth is covered in massive ice sheets,
and global sea levels drop, like it was back
when humans could just walk over into North America.
We call those Ice Ages.
Milankovitch cycles can also add plenty of extra energy
into Earth's budget to warm the planet back up.
Which is why I can't walk to Siberia today.
Of course, by this point you won't be surprised
to learn that scientists have these patterns
really well calculated these days, and yeah,
they're not enough to explain recent global warming either.
(gentle music)
This is not a comprehensive list
of all the natural forces that can influence the climate.
There's several other factors that scientists consider
when trying to figure out the cause of all of this,
like how dark or light land and ocean are,
and therefore how much solar energy they absorb or reflect.
Take ice caps, for instance.
As they get dirtied by soot and ash
from distant fires and smokestacks,
that ice gets slightly darker and absorbs more heat.
Or when forested areas are cleared,
sometimes land gets lighter in color, and absorbs less heat.
So what does it all mean?
I've made it this far into the video,
you're saying to yourself.
Give me the payoff! Well, here it is.
Scientists are very aware of these natural cycles
and natural factors that influence the climate.
They're aware of them because it was climate scientists
who discovered these things.
They didn't just decide one day to start ignoring them.
These natural effects are already factored
into our climate models, so if you think
that palm trees in Antarctica or random warm periods
