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Why are global
Topic 5.4
 What
does the graph on page 36 tell us
about the climate over the past 150
thousand years?
 What does the 2nd graph on page 36 tell
us about the climate in the last 250 years?
Why are global temperatures
 Changes
in the atmosphere are linked to
climate change
 Atmosphere:
 Thin layer of gases extending about
100km upwards. These gases are retained
by the earth’s gravity.
What are the layers?
These layers are necessary.
Warm the earth, stop temperature fluctuation between day and night,
absorb harmful UV rays
How does the atmosphere keep the Earth at a constant liveable
Troposphere (15km)
Stratosphere - part is the ozone layer (next 35km)
Greenhouse gases in the troposphere
Carbon dioxide, methane, nitrous oxide, chloroflurocarbons
 Greenhouse
house Effect
 The greenhouse effect itself is essential to
human life. An increase in this effect is
thought to have negative effects.
Greenhouse gases
 Read
page 38
 How
can we measure their
greenhouse effect?
 Using GWP (global warming potential)
 This
is a measure of the greenhouse effect
caused relative to carbon dioxide which
is given the value 1.
Changes in CO2 and
Temperature in the past
160,000 years
Does increased carbon
dioxide cause global
 Before
the industrial revolution, what
caused the temperature to change?
 Earth’s orbits around the sun changes
solar radiation and volcanic eruptions.
How does an increase in temperature affect
the levels of carbon dioxide?
Increases it.
Where did the extra carbon dioxide come
The oceans, there is less water in the oceans
and less CO2 dissolved at higher temperature
 After
the industrial
revolution CO2 levels rose
followed by a rise in
 What
is going to happen to
the global temperature?
 Probably rise – carbon
dioxide is at the highest
level than in last 400 000
What is meant by the term
Global Warming?
A rise in the average global temperature of
the earth’s surface.
Scientific consensus has it that it is at least in
part caused by increased greenhouse gases
like CO2.
These gases trap infra-red rays emitted by the
earth’s surface.
This rise in average global temperature has
lead to climate change, melting of the polar
Climate change - A
controversial issue
Why might some people disagree that global
warming is occurring or that it is caused by human
Science can only disprove theories, not prove
Correlation does not equal causation
Limitations of the data: we can’t measure exactly
how much of each gas comes from each source
Computer models overestimated 2000 CO2 levels
Evidence can be interpreted in different ways:
money and power can influence decisions