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  • - [Narrator] Glaciers have been shaping

  • our world for millions of years.

  • But as climate change warms the planet,

  • glaciers are disappearing, not only altering the landscapes

  • they leave behind, but changing our oceans, weather,

  • and life on earth as we know it.

  • A glacier is a huge mass of ice that moves slowly over land.

  • Glaciers can be classified into two general groups

  • alpine glaciers and ice sheets.

  • Alpine glaciers form on mountainsides

  • and move downward through valleys.

  • Sometimes, they create valleys by pushing dirt, soil,

  • and other materials out of their way.

  • These glaciers are found

  • on every continent except Australia.

  • Ice sheets, unlike alpine glaciers,

  • are not limited to mountainous areas.

  • They form broad domes and spread out

  • from their centers in all directions.

  • As ice sheets spread, they cover everything around them

  • with a thick blanket of ice, including valleys,

  • plains, and even entire mountains.

  • The largest ice sheets are called continental glaciers.

  • They cover vast area including most of Antarctica

  • and the island of Greenland.

  • Glaciers can form over years

  • when more snow piles up and melts.

  • Soon after falling, the snow begins to become denser

  • and more tightly packed.

  • When new snow falls and buries the previous years snow,

  • the bottom layer becomes even more compressed.

  • The dense, grainy ice that has survived

  • one year's melt cycle is called firn.

  • When the ice grows thick enough, the firn grains fuse

  • into a huge mass called glacial ice.

  • The glacier may begin to move under its own weight,

  • through a process called compression melting.

  • As they move, glaciers erode or wear away

  • the land beneath and around them.

  • When glaciers began their latest retreat

  • less than 20,000 years ago, they left behind

  • many landscape features,

  • such as lakes, valleys, and mountains.

  • Glaciers provide people with many useful resources.

  • Glacial till provides fertile soil for growing crops.

  • And, deposits of sand and gravel are used

  • to make concrete and asphalt.

  • Many rivers are fed by the melting ice of glaciers.

  • The most important resource provided

  • by glaciers is freshwater.

  • Earth's average temperature has been increasing

  • dramatically for more than a century.

  • Glaciers can act as indicators of global warming

  • and climate change in several ways.

  • Melting ice sheets contribute to rising sea levels.

  • As ice sheets in Antarctica and Greenland melt,

  • they raise sea levels, adding fresh water

  • to the ocean every day.

  • The loss of glacial ice also reduces the amount

  • of fresh water available for plants and animals on land.

  • Large additions of fresh water change

  • the ocean ecosystem, as well ocean currents.

  • Additionally, less salt in the ocean could disturb

  • the gulf stream, drastically changing

  • the weather on land as well.

  • Since glaciers are so sensitive to climate change,

  • the increased speed of glacier melt

  • is an early warning system for the rest of the planet.

  • And if global warming goes unchecked, many, if not all,

  • alpine glaciers could disappear completely.

  • (soft entertaining music)

- [Narrator] Glaciers have been shaping

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