Transcript U3A-ClimChange10 3041KB Nov 22 2012 05:40:24 PM

CLIMATE CHANGE
THE GREAT DEBATE
Session 10
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
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
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
WARMER CLIMATES (1)
Predictions are that if warming continues:
(1) Global precipitation will increase but
distribution will also change
(2) Increased cloud cover
(3) Less snowfall and frost
(4) Increased monsoon effects
(5) Distribution and intensity of tropical
cyclones will increase
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
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
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
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
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
During the last
160,000 years
air temperature
and the amount
of CO2
have been
closely related
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?
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
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
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
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