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A Channel 4 documentary "The Great Global
Warming Swindle" claims that man-made global
warming is "a lie" and "the biggest scam of
modern times." The documentary says the Earth
has warmed and cooled throughout history. The
recent climate changes are natural, it claims.
What is a theory?
Theories are ideas created by
scientists to explain why things happen.
A theory explains evidence from
observations or experiments.
It predicts future
observations.
A theory can be tested
by making observations
and doing experiments.
Global warming
Global warming is the rise in
temperature of the Earth's atmosphere.
Many scientists
believe that
greenhouse
gases cause
global warming.
Global warming causes climate change.
Climate change
The Earth's climate has always been
changing.
Now, climate
change
means
changes in
our climate
since 1900.
Greenhouse gases
Greenhouse gases trap heat from the
Sun. They make up about 1% of the
Earth's atmosphere.
Carbon dioxide (CO2)
is a greenhouse gas.
Without greenhouse
gases, the Earth would
be 30°C colder.
Humans could not survive.
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There is evidence that
the world is getting
warmer.
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There is evidence that
the current temperature
rise is unusual.
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There is a fairly strong
correlation between CO2
levels and atmospheric
temperatures.
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There is evidence that
human activity causes
rising carbon dioxide
levels.
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There is evidence that
global warming causes
more extreme weather.
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There is evidence that
humans could prevent
global warming.
Theory A: Human activity causes global warming
Burning fossil fuels
Extra greenhouse gases make
releases greenhouse
global temperatures rise.
gases into the atmosphere. This leads to climate change.
The evidence:
Global temperatures have gone up by
0.7C since 1700.
Most warming was between 1910 and 1940
and after 1976.
Many scientists agree that
increasing amounts of
greenhouse gases have made
global temperatures go up.
The 1990's was the warmest decade of the
last thousand years.
Scientists predict that increasing
global temperatures will make sea
levels rise.
Before the industrial revolution, 0.028% of
the atmosphere was CO2. Now the level is
0.037%.
The increase in CO2 is linked to human
activity.
The concentration of CO2 in our atmosphere
is higher now than it has been for 650,000
years.
Scientists predict more intense
hurricanes.
Carbon dioxide takes 100 years to
disperse. If we stop making carbon
dioxide now, the effects of what we
have already done will influence
our weather for years.
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Theory B: Global warming is natural
The Earth has gone through many cool and warm periods. Human activity is not
significant when you
The causes of these climate changes are complex.
consider all the factors
that affect climate.
The evidence:
Global temperatures have gone up by 0.7C
since 1700. This is not significant. Global
temperatures actually decreased between 1940
and 1976.
Satellites and balloons have measured
atmosphere temperature since 1979. This data
shows little warming up to 8 km above the Earth’s
surface.
Water vapour is the most important
greenhouse gas. It makes up 95% of all
greenhouse gases in the atmosphere. Water
particles in clouds reflect heat from the Sun.
“The Great Global Warming Swindle” says that
human activity makes 6.5 gigatonnes of CO2 each
year. Plants and other animals make 150
gigatonnes each year. Dying leaves make even
more CO2. The oceans are the biggest source of
CO2.
CO2 levels in the atmosphere increase
or decrease because of temperature
change. When the climate cools,
oceans absorb CO2. When the climate
warms, oceans release CO2.
Solar activity influences global warming
and cooling more than any activity on
Earth. Solar activity is now very high.
This may have caused recent record
temperatures.
Current global warming is nothing
unusual. Temperatures were even
more extreme in the Medieval Warm
Period.
It is difficult to link weather events like
hurricanes to global warming. The
climate of the world is always
changing.
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