Lesley Monk

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Lesley Monk Balfron High School Session 2005/6
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GLOBAL WARMING ARE WE TO BLAME ?
This is one of the most frequently asked
environmental questions in recent times. That
the planets climate is changing, there is no
doubt. But who or what is the reason for this is
a hotly debated point. We shall put the evidence
in front of you and let you decide!
We really dont know !
So what is the answer ?
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Graph 1 shows the temperature of the Earth over 1
million years. Note the line showing todays
average temperatures, and the arrow to the last
Ice Age. Graph 2 is a close-up from the last few
years of the Ice Age till today. Graph 3 shows
the time since the Vikings began raiding Britain.
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1. ICE CORE ANALYSIS-Air trapped in ancient snow-
now ice- can show what the atmosphere was like
millions of years ago.
2. TREE RING ANALYSIS-Tree rings record good and
bad years for tree growth and can go back to
prehistoric times.
WHAT EVIDENCE IS THERE OF GLOBAL WARMING ?
4. POLLEN ANALYSIS-This will show the types of
plants that were growing in an area millions of
years ago, and we can work out the likely
conditions from comparison with todays plant
needs.
Copy text
3. OCEAN FLOOR SEDIMENTS-The mud in the ocean
deep has been there for millennia and can be
analysed for oxygen isotopes.
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So you can see that our planet hasnt exactly had
a stable climate !
But are we responsible for the changes, or is it
natural forces at work?
Read pages 25 and 26 of the booklet. You will
need to be able to discuss each of these factors
in a way that shows you appreciate their
potential importance.
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There are different possible causes of these
raised temperatures. They fall into two
categories- Physical and Human.

• Physical Factors
• Solar variation
• Volcanic activity
• Ocean currents
• Milankovitch cycles

• Human Factors
• Burning fossil fuels
• Increased output of methane etc.
• Deforestation

Lets look at each in turn.
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PHYSICAL 1 - SOLAR VARIATION
Sunspots an increase in sunspot activity may
lead to a very slight increase in the suns
output and a temporary warming of the earth.
Sunspot activity follows 11 and 22 year
cycles. The Little Ice Age of 1450-1700 may have
been linked to periods of very low sunspot
activity.
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PHYSICAL 2 - VOLCANIC ERUPTIONS

• Eruptions of volcanoes can throw millions of
  tonnes of ash,dust and sulphur dioxide into the
  atmosphere.
• This produces aerosols that can reduce the amount
  of sunlight reaching the earth.
• This can lead to a temporary cooling of the earth.

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VOLCANIC ERUPTIONS 2

• Major eruptions in the past which have been
  linked to short periods of global cooling
  include-
• Tambora (1815),
• Krakatoa (1883),
• Mt. St Helens (1980)
• Pinatubo (1991)

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PHYSICAL 3 OCEAN CURRENTS
Changes in the pattern and strength of ocean
currents may lead to changes in the distribution
of heat around the planet.
A short term example
would be El Niño, which appears every few years.
A longer term example would be the North Atlantic
Drift, which may change position every few
thousand years.
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ENSO - the El Niño Southern Oscillation
Every 2-7 years the western Pacific becomes much
warmer, disrupting weather patterns - possibly on
a global scale.
The normal conditions, with cool surface water
off the coast of Peru.
An El Niño year
A La Niña year
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One theory suggests that global warming will
increase the number of icebergs in the Atlantic,
cooling the sea and switching off the North
Atlantic Drift / Atlantic Conveyor system. This
would be bad news for us!
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PHYSICAL 4 - MILANKOVITCH CYCLES

• Milankovitch cycles are three variations in the
  earths orbit. Although they may be linked to
  very long term changes in the climate, their
  effect would not be noticed on a scale of a few
  hundred years.

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HUMAN FACTORS THE ENHANCED GREENHOUSE EFFECT.
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These are the main greenhouse gases
See how they have increased over the years of
industrial activity.
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HUMAN 1 - BURNING FOSSIL FUELS

• The fossil fuels are-
• COAL
• OIL
• NATURAL GAS
• They are called fossil fuels because they are
  formed from the remains of ancient plants (coal)
  and marine animals (oil).

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When we burn these fuels, we release millions of
tonnes of Carbon Dioxide (CO2) into the
atmosphere.
There has been an enormous increase in these
greenhouse gases since the Industrial Revolution
began about 200 years ago.
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Power stations are one of the main producers of
greenhouse gases such as Carbon Dioxide.
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Environmental campaigners all over the world are
demanding cuts in CO2 emissions. Here Greenpeace
uses a light display to get its message across.
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Vehicle exhausts are the main source of Nitrous
Oxides.
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HUMAN 2 - INCREASED METHANE
I am a ruminant - when I digest grass, I produce
methane - lots of it!

• A cow can burp / fart about a quarter of a kg.
  of methane a day.
• The number of cattle has doubled in the past 40
  years. Sheep, goats and camels are also
  ruminants.
• There are now 1.3 billion cattle, each burping /
  farting methane several times a minute!
• The New Zealand government is proposing to bring
  in a flatulence tax on cattle farms.

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The huge increase in world population and in the
area of land given over to crops in general and
to rice production in particular, has led to a
rapid rise in global methane production. Farmland
for rice has doubled in 45 years.
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HUMAN 3 - DEFORESTATION
Forests absorb CO2 and release oxygen
...if they are cut down, atmospheric levels of
CO2 must rise as a consequence.
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• Clearing forest by burning releases huge amounts
  of stored CO2 back into the atmosphere.
• The smoke from the fires also adds to global air
  pollution.

This is known as a double- whammy !
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KEY TERMS TO REMEMBER

• Solar variation / Sunspots
• Volcanic eruptions /Sulphur dioxide /Aerosols
• Milankovitch cycles
• El Niño
• Enhanced Greenhouse effect
• Carbon Dioxide / Methane / Nitrous Oxides
• The Industrial Revolution / burning fossil fuels
• Padi fields / cattle / methane production
• Deforestation

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CONGRATULATIONS !!
You have now finished the Higher Geography
Course! All that remains is to learn it all!