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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 likeEarth is a planetand

  • air is realyet 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.

[MUSIC]

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