CLIMATE CHANGE

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CLIMATE CHANGE
THE GREAT DEBATE
Session 10
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CLIMATE CHANGE?

• If we have learnt anything from this course, it
  is that climate is not constant
• It is, and always has been, changing
  continuously, either warming or cooling
• Most of the factors involved are out of our
  control but today is not the first time that
  biological factors are having an influence on
  climate

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WARMING OR COOLING?

• If we have a choice would we prefer a warmer or a
  cooler climate?
• It is obvious from the historic past that we have
  experienced both warmer and cooler climates than
  we are living with today. These changes have not
  been large but even so they have had a big impact
  on human populations

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COOLER CLIMATES

• In the last 2000 years there have been at least
  two periods of cooler conditions. The Dark Ages
  from 530 to 900 AD and the Little Ice Age from
  1300 to 1850 AD
• Agriculture was restricted at high latitudes and
  high altitudes. Elsewhere, there were periods of
  drought, famine, war and disease. Throughout
  Western Europe there were times of population
  decline during cold extremes

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WARMER CLIMATES (1)

• Predictions are that if warming continues
• Global precipitation will increase but
  distribution will also change
• Increased cloud cover
• Less snowfall and frost
• Increased monsoon effects
• Distribution and intensity of tropical cyclones
  will increase

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WARMER CLIMATES (2)

• (6) Sea levels will rise
• (7) Rates of plant growth will increase
• (8) Pests and diseases will proliferate
• (9) Many crops will grow at higher latitudes and
  altitudes
• (10) Reduction in heating but increase in air
  conditioning
• (11) Relocation of winter sports

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CLIMATE MODELS

• Computer models have are being used extensively
  to predict future climates
• They are usually based on a doubling of
  greenhouse gases
• Some of the predictions are rather alarming,
  especially those relating to sea level rise
  changes from 0.3 to 1.5 meters have been
  predicted

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MODEL SHORTCOMINGS

• They are extreme simplifications of the real
  Earth
• They keep all other factors that may affect
  climate constant and change only the level of
  greenhouse gases
• They are only as good as the data that have been
  entered into them
• They ignore possible changes in ocean currents
  and cloud cover

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SEA LEVEL CHANGES

• They are a major concern for those living in
  low-lying coastal areas
• Sea level has been rising since 1880 and since
  1930 the average rate has been approximately 2.5
  mm/year
• The rise is not only due to melting glacial ice
  but also to expansion of the volume of ocean
  water as it warms

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CARBON DIOXIDE CHANGES

• Ice cores from Antarctica contain small amounts
  of air trapped at the time the ice was formed
• Analysis of air samples enables us to determine
  how the CO2 content of the atmosphere has changed
  over time
• It shows that during glacial times the CO2
  content was much lower than during interglacial
  times, including the Holocene

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During the last 160,000 years air temperature and
the amount of CO2 have been closely related
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CAUSE OR EFFECT?

• In recent years it has become possible to sample
  at much closer time intervals and it appears that
  temperature rises first followed by a rise in CO2
• We presume this happens because when the ocean
  waters warm their ability to hold CO2 in solution
  is reduced and some of the gas is passed into the
  atmosphere where it could cause further warming
  but is it significant?

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WATER VAPOUR THE ULTIMATE GREENHOUSE GAS

• About 98 of the greenhouse effect is due to
  water vapour in the atmosphere
• Because there is a super abundance of water on
  our planet, its concentration in the atmosphere
  is controlled by the temperature of the Earth,
  not the other way round
• It cannot initiate a rise or fall in temperature
  but it has the effect of magnifying the change.
  This is called a positive feedback effect

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Climate sceptics such as Plimer claim that
increases in greenhouse gases so far have been
tiny compared with the amount, mostly water
vapour, that was already in the atmosphere
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ARE SCEPTICS RIGHT?

• If they are right, recent climate changes have
  been driven by changes in orbital movements and
  energy output from the Sun but are greatly
  magnified by water vapour in the atmosphere
• They believe that the increase in carbon dioxide
  and other greenhouse gases only plays a minor
  role and so far has not significantly affected
  our climate

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FUTURE TEMPERATURE TRENDS

• If the Believers are right the planet will
  continue to warm ever more rapidly in the next
  few decades
• If the Sceptics are are right, we can expect to
  see significant cooling because the current
  sunspot cycle is particularly weak and this is
  known to have caused significant cooling in the
  historical past

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