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  • Twenty thousand years ago, the Earth was a frigid landscape where woolly mammoths roamed.

  • Huge ice sheets, several thousand meters thick, encased parts of North America, Asia, and Europe.

  • We commonly know it as the "Ice Age."

  • But geologists call it the Last Glacial Maximum.

  • That's because it's the most recent time that ice reached such a huge extent, andice ageis an informal term without a single agreed-upon definition.

  • Over the last million years, there have actually been about 10 different glacial maxima.

  • Throughout Earth's history, climate has varied greatly.

  • For hundreds of millions of years, the planet had no polar ice caps.

  • Without this ice, the sea level was 70 meters higher.

  • At the other extreme, about 700 million years ago, Earth became almost entirely covered in ice, during an event known asSnowball Earth.”

  • So what causes these massive swings in the planet's climate?

  • One of the main drivers is atmospheric carbon dioxide, a greenhouse gas that traps heat.

  • Natural processes, such as volcanism, chemical weathering of rocks, and the burial of organic matter,

  • can cause huge changes in carbon dioxide when they continue for millions of years.

  • Over the past million years, carbon dioxide has been relatively low, and repeated glacial maxima have been caused by cycles in Earth's movement around the sun.

  • As Earth rotates, it wobbles on its axis and its tilt changes, altering the amount of sunlight that strikes different parts of its surface.

  • These wobbles, combined with the planet's elliptical orbit, cause summer temperatures to vary depending on whether the summer solstice happens when Earth is closer or farther from the sun.

  • Approximately every 100,000 years, these factors align to create dramatically colder conditions that last for millennia.

  • Cool summers that aren't warm enough to melt the preceding winter's snow allow ice to accumulate year after year.

  • These ice sheets produce additional cooling by reflecting more solar energy back into space.

  • Simultaneously, cooler conditions transfer carbon dioxide from the atmosphere into the ocean, causing even more cooling and glacier expansion.

  • About 20,000 years ago, these trends reversed when changes in Earth's orbit increased summer sunshine over the giant ice sheets, and they began to melt.

  • The sea level rose 130 meters and carbon dioxide was released from the ocean back into the atmosphere.

  • By analyzing pollen and marine fossils, geologists can tell that temperatures peaked about 6,000 years ago, before another shift in Earth's orbit caused renewed cooling.

  • So what's coming next?

  • Based on the repeated natural cycle seen in the climate record, we'd normally expect the Earth to continue a trend of gradual cooling for the next few thousand years.

  • However, this cooling abruptly reversed about 150 years ago.

  • Why?

  • Carbon dioxide levels in the atmosphere have been rising since the 19th century, when fossil fuel use increased.

  • We know that from studying air bubbles trapped in Antarctic ice.

  • This surge in carbon dioxide also coincides with a global temperature increase of nearly one degree Celsius.

  • Ice cores and atmospheric monitoring stations show us that carbon dioxide levels are rising faster, and to higher levels, than at any point in the last 800,000 years.

  • Computer models forecast another one to four degrees Celsius of warming by 2100, depending on how much additional fossil fuel we burn.

  • What does that mean for the ice currently on Greenland and Antarctica?

  • Past climate changes suggest that even a small warming shift can begin a process of ice melt that continues for thousands of years.

  • By the end of this century, ice melt is expected to raise the sea level by 30 to 100 centimeters, enough to impact many coastal cities and island nations.

  • If a four-degree Celsius warming persisted for several millennia, the sea level could rise by as much as 10 meters.

  • By studying past climates, scientists learn more about what drives the shifts in ice that have shaped our planet for millions of years.

  • Research suggests that by taking action now to reduce carbon dioxide emissions quickly, we still have the opportunity to curb ice loss and save our coastal communities.

  • If your'e a student watching this now, we have a question for you.

  • Do you ever feel like you're too young to have any real impact on climate change?

  • If so, we disagree.

  • All these students in our Ted-Ed clubs program are speaking up and taking action to fight for a healthy, habitable planet.

  • And maybe the next great idea or well-chosen word will change the world or change someone's mind will be yours.

Twenty thousand years ago, the Earth was a frigid landscape where woolly mammoths roamed.

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B2 US TED-Ed carbon dioxide dioxide carbon earth cooling

When will the next ice age happen? - Lorraine Lisiecki

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    Evangeline posted on 2021/02/26
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