中級 2844 タグ追加 保存
動画の字幕をクリックしてすぐ単語の意味を調べられます!
単語帳読み込み中…
字幕の修正報告
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,
and “ice age” is 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 as “Snowball 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.
コツ:単語をクリックしてすぐ意味を調べられます!

読み込み中…

When will the next ice age happen? - Lorraine Lisiecki

2844 タグ追加 保存
Evangeline 2018 年 6 月 17 日 に公開
お勧め動画
  1. 1. クリック一つで単語を検索

    右側のスプリクトの単語をクリックするだけで即座に意味が検索できます。

  2. 2. リピート機能

    クリックするだけで同じフレーズを何回もリピート可能!

  3. 3. ショートカット

    キーボードショートカットを使うことによって勉強の効率を上げることが出来ます。

  4. 4. 字幕の表示/非表示

    日・英のボタンをクリックすることで自由に字幕のオンオフを切り替えられます。

  5. 5. 動画をブログ等でシェア

    コードを貼り付けてVoiceTubeの動画再生プレーヤーをブログ等でシェアすることが出来ます!

  6. 6. 全画面再生

    左側の矢印をクリックすることで全画面で再生できるようになります。

  1. クイズ付き動画

    リスニングクイズに挑戦!

  1. クリックしてメモを表示

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔