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Glacial ice
1.1.1
1.1.1
2.2.32.3.2

What tipped the Earth into the Quaternary?

While the Milankovitch Cycles can help explain long-term
movements between glacial and interglacial mes, and
volcanic ac vity can explain short term cooling, there is s ll a
need to explain what event heralded the onset of the
Quaternary ice age. Some have suggested a long-tern decline
in global CO₂ levels, although this process was long under
way prior to the onset of the Pleistocene.
Three million years ago the South American con nent
moved closer to North America. The collision of the two
plates created volcanic islands and raised the narrow isthmus
which today connects the two con nents through Panama.
This land separated the Pacific Ocean from the Atlan c and Fig.212 The Gulf Stream, by taking warm waters north,
prevented the movement of warm, Equatorial ocean currents may well have helped p planet Earth into an ice age.
between the two oceans. The result was the emergence of during the summer months, further cooling the climate.
the Gulf Stream and North Atlan c Dri in the Atlan c.
This posi ve feedback mechanism allowed sea ice to
Moisture evaporated from warm seas created by these form in the Arc c which, unlike sea water, reflects most of
currents fell as snow over the colder land at higher la tudes. the solar radia on which falls upon it. As the sea ice spread
This snow acted to reflect solar radia on back into space and south temperatures cooled further, plunging the Earth into
a general cooling occurred. This allowed more ice to remain the first glacia on of the Quaternary epoch.

What is the greenhouse effect? Fig.213 Greenhouses trap in heat

People grow fruit and vegetables in quickly in the morning and stay warmer
greenhouses because they create warm for longer at night.
condi ons in which plants grow faster
In the atmosphere, certain gases act
and fruit ripens more quickly. Glass
in the same way as greenhouse glass,
panels allow short-wave solar radia on trapping heat within the atmosphere.
to pass into the greenhouse. Here it is The most important greenhouse gas is
absorbed by the plants and warms the water. No ce how temperatures fall
soil. The heat is then radiated back much further and faster on a clear night
from the soil as long-wave infrared than when it is cloudy. The cloud
radia on. The 'trick' of the greenhouse droplets and water vapour act like glass respira on, and methane (CH₄),
is to allow short-wave radia on in but
trapping heat in the lower atmosphere. produced by the ro ng of organic
to trap long-wave radia on within the material, are also greenhouse gases.
Water is an excellent greenhouse
structure. Greenhouses warm up more For much of the Quaternary CO₂ levels
gas as it can absorb a lot of energy. In
fact, without water in the atmosphere have remained rela vely constant at
global temperatures would be around 250 parts per million (ppm).
1. Describe how sunspots significantly lower than today. This is a ny amount compared to the
may affect climate on Earth. (3) 780,840ppm of atmospheric nitrogen
However, the important thing about and 209,460ppm of oxygen. Methane
2. With reference to examples, water vapour is that it doesn't stay very levels have tended to fluctuate with
explain how volcanic erup ons can long within the atmosphere. Within a changes in global temperatures, but for
alter the climate of the planet. (5) few days water vapour will leave the most of the Quaternary methane has
3. Describe what is meant by the atmosphere as precipita on, albeit to hovered around 700 parts per billion.
Milankovitch Cycles. (3) be replaced by moisture evaporated
elsewhere. A balance exists between
4. Explain how one or more of the evapora on and precipita on within KEY TERMS
Milankovitch Cycles impacts on
the atmosphere as a whole. This helps
global temperatures. (4) Greenhouse gas: an atmospheric gas
stabilise atmospheric temperatures. which can absorb infrared radiation
5. How can the movement of Water is not the only greenhouse coming from the Earth’s surface, acting
tectonic plates affect Earth’s climate? gas. Carbon Dioxide (CO₂), emi ed by to increase global temperatures.
(4) living organisms as a bi-product of Greenhouse gases include water,
methane and carbon dioxide.

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The climate has changed from the start of the Quaternary period.