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7/31/2019 Des Withanimation

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An ice age, is a period of long-term reduction inthe temperature of the Earth's surface and atmosphere,resulting in the presence or expansion of continental ice

sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual pulses of cold climate are termed

"glacial periods" and intermittent warm periods are called"interglacials".


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Agassiz amassed more evidence from landforms and boulder clays to support his idea of a Great Ice Age in recent times.

Glen Roy, Scotland

Parallel marks showformer level of anice-dammed lake


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Pollen

MammothBeetles

Fossil discoveries alsosuggested that climate hadrecently been much colder .

Beetles and pollen grainsfound in sediments associatedwith the boulder clays wereidentified as types known only

from the Arctic tundra today.

Woolly mammoths founddeep frozen in Siberia hadfur adapted to tundra life.


8/22 Annual layers in ice

Drilling cores

In the early 1980s, therewas another majorbreakthrough.

Cores were drilled in thepolar icecaps revealingannual layers of snow going

back thousands of years.


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When the Last Ice Age was at its maximum, ice sheets coveremuch of Europe and North America.

So what actually caused it?


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In the 1940s, Milankovi wondered whether wobbles in theEarths orbit around the Sun could explain multiple Ice Ages by

changing the amount of heating reaching the Earth

Milutin Milankovi (1879-1958)


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Milankovi added up all the orbital wobbles and predicted thatice ages should occur in regular cycles - probably happening

every hundred thousand years or so.


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In 1960s, deep sea records showed that Milankovi was right!

c o

l d

h o

t

1000s of years before present

The Oil Drum

The Earths climate had repeatedly blown hot and cold withice age cycles happening every hundred thousand years just

as Milankovi had predicted.


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NOAA

Greenhouse Gas levelsdropped during Ice Ages

Last Ice Age =

Low Greenhouse Gas

The second idea is thatchanges in greenhousegas levels were to blame.

Greenhouse gases help tosoak up sunlight and keepthe Earth warm.

Air bubbles in ice coresshow that levels fell duringIce Ages so this mayhave sped up cooling.


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Gulf Stream warms the Arctic Some scientists believethat ocean currents likethe Gulf Stream

were important.

This current helpswarm up the Arctic. If itswitched off thiswould cool the Arcticfurther andincrease the likelihood ofan Ice Age


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Much of the worlds water from seas and oceans got frozen. As aresult , sea level droppedPlaces that had been under water become dry landMany plants and animals adapt to these changes but many died


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The next ice age is more than 15,000 years away, according to

evidence from an Antarctic ice core, the deepest and oldest ever extracted.

The core gives us a 740,000-year record of the planet's climate,including the past eight ice ages, and interglacials in between.

The core was more than 3 km long and measured to be 740,000years old at its farthest end.

The core gives a picture of the Earth's cycles of warm and cold,reflected in the different thicknesses of ice that fell on Antarcticaas snow.


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