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[MUSIC]
Let’s not beat around the rapidly melting
iceberg here: climate change is happening,
and we’re causing it. The evidence is overwhelming.
Scientists usually reserve this level of agreement
for claims like “Earth is a planet” and
“air is real” yet here we are, the climate
change ship has now left the dock, and lots
of people on shore are still debating whether
boats can actually float.
BUT, maybe you’re a person who trusts and
accepts what climate scientists are telling
us, it’s just sometimes it’s hard to explain
why. I mean we’ve all been there…
I mean I care about the environment. I figure
with the polar bears and everything we might
as well try electric cars. What do we have
to lose?
And then they go CAPS LOCK SERIOUS saying
they have proof that climate change is a hoax
perpetuated by scientists paid off by the
Polar Bear Lobby as part of a plan to install
Al Gore as supreme world polar bear emperor.
WAKE UP SHEEPLE!
To keep that from happening, we put together
this handy reference.
The sun is the source of warmth on Earth,
so thanks for that, Sun. Ice and clouds reflect
some of its light away, and the rest is absorbed
by land and water and re-emitted as heat.
Some heat escapes to space, and some is held
in by the atmospheric greenhouse effect.
The insulating effect of Earth’s greenhouse
gases are the reason that life exists as we
know it, but human activities have increased
the concentration of one of em, carbon dioxide,
40% since the Industrial Revolution.
We know the sun’s output has varied during
history, but since 1970s, the period when
global temperatures increased in the fastest,
temperature and solar activity have moved
in opposite directions.
If the sun was to blame, it would cook the
upper and lower layers of atmosphere together.
Instead, we only see warming in the lower
layers, the same place that human greenhouse
gases like carbon dioxide are piling up.
Since 1870, with fossil fuels, cement production,
and land use combined, humans have put about
2,000 gigatons of CO2 into the atmosphere,
that's two million million tons, and about
40% has stayed there.
Studying gases trapped in ice cores have let
us see what Earth’s atmosphere was like
in the past. At more than 400 parts per million,
today’s CO2 levels are the highest they’ve
been for almost a million years. That’s
before humans even existed, totally uncharted
territory for us.
More carbon dioxide in atmosphere means average
temperatures across the globe are increasing,
and fast. Right now, Earth is warming about
ten times faster than at the end of an ice age
Ok, so CO2 is increasing. How do we know it's
our fault? The best evidence comes from looking
at what isotopes, or different kinds of carbon,
are in the atmosphere.
Fossil fuels come mainly from old plants.
Plants prefer to use the lighter isotope carbon-12
over the heavier carbon-13, so they contain
a higher ratio of 12 to 13 than the atmosphere
does.
When more fossil fuels get burned, the percentage
of carbon-12 in the atmosphere should go up,
and that's exactly what we see.
And it's not because of volcanic activity.
Volcanoes only emit about 1% as much CO2 as
we do.
Normally that CO2 is balanced and exchanged
between the atmosphere, plants, and animals,
but eliminating carbon sinks has released
centuries worth in just a few years.
Other greenhouse gases are also increasing,
like methane from farm animals and natural
gas processing, or nitrous oxide from fertilizers.
If we run simulations just using natural causes
of climate change, they predict no change,
or even cooling in 20th century and that is
not what’s happening.
[OMINOUS MUSIC]
It's still gonna get cold in some places,
but in 2000s there were twice as many record
highs as record lows. Each of the past three
decades has been warmer than any other decade
since we started measuring in 1850.
Since 1900, actual temperatures around the
world increased almost a full degree, and
most of that has happened since the 1970's.
Looking at data from tree rings and ice cores,
the past 30 years is probably the warmest
in eight centuries.
Of course, not every place on Earth warms
equally.
Oceans cover more than 70% of Earth, and they
absorb more than 90% of the heat added to
the planet. Naturally, that’s where we see
most extreme changes.
Around the world, oceans are rising a tenth
of inch per year, and they’re up 8 inches
since 1901.
This is because water expands as it warms,
and when ice sheets and glaciers melt in Greenland
and Antarctica, water that’s normally on
frozen land gets put in the ocean.
The oceans are Earth's largest carbon sink.
As more CO2 enters atmosphere, more of it
dissolves in the ocean, which makes the water
more acidic.
This doesn’t mean that the oceans will be
made of acid, but animals with calcium shells
are super-sensitive to pH. We’re on course
for the oceans to hit pH 7.8 in 100 years,
which could wipe out one-third of species
in the ocean.
We also know that levels of summer sea ice
in the Arctic have decreased 40% since 1978,
they might be the lowest levels in 1400 years.
That white sea ice usually reflects the sun’s
energy back into atmosphere, but the dark
ocean is soaking it up like a black shirt
on a sunny day, which feeds the cycle forward.
If CO2 emissions continue on their current
trends, Earth is on course to be 2.5-5 degrees
warmer, and the oceans could be up to a meter
higher, by the end of this century
Is that a big deal? Yeah! It's the biggest
deal. This is by far the greatest issue facing
our species. The last time the Earth averaged
a few degrees colder, most of North America
was covered in a mile-thick sheet of ice.
That many degrees warmer? We're gonna have
a bad time.
So now you're armed with the facts. Why we
know climate change is happening, and why
we’re causing it. Please, share this information
with the people you know, and let me know:
Did it change any minds? Did it change your
mind?
I mean, are facts enough?
If not, then why do so many people continue
to NOT believe in climate science?
We'll answer that question in our next video.
Stay curious.
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VocabularyClimate Science: What You Need To Know
Learn the basic science of climate change in 24 easy steps
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