1. Lecture 1
Weather, climate and the
greenhouse effect
LSGI1B02 Climate Change and Society
Reading: (Burrough, 2007, Chapters 1 and 2; Houghton
Chapter 2, Maslin Chapter 1)
2. Definitions
• Important to discriminate b/w weather and
climate
– Weather is what we get – what is happening to
the atmosphere at any time
– Climate is what we expect- what statistics tell
us- based on averages, therefore useful for
recognising extreme weather. Needs long time
series
• Boundary b/w weather and climate blurred
by changing frequency of extreme weather-
may influence our perception of climate
4. Climate variability and climate change
Variability refers to fluctuation about the mean
1. Climate may be highly variable but there is no climate change
Time
Temperature
5. Climate variability and climate
change
2. Variable climate may be accompanied by climate
change responding to a ‘forcing’ factor (Maslan
Fig. 5) - this change can be
a. A long-term trend
b. Muted or limited response due to buffering
c. Delayed or non-linear response: slow due to
buffering then sudden non-linear response
d. Threshold response: initially no response, then all
response in one large ‘step’
7. Climate variability and climate
change
3. Variability does not remain constant
a. Amplitude of variability may change while
climate constant
b. Variability may change as climate changes
c. Sudden change in climate may alter
amplitude of variability
Burroughs Figure 1.2
9. Systems theory and Feedback
mechanisms
• In systems, everything is connected to
everything else
10. Positive feedback
• Some changes are self-reinforcing, bringing dramatic
change (positive feedback)
• Positive feedback causes change and instability
B has positive effect on A, and A has positive effect on B eg. population growth
11. Negative feedback
• Others may be counter-active, and reverse the
original change (negative feedback)
• Opposes change: keeps things the same
http://gerrymarten.com/human-ecology/chapter02.html#p2
12. Feedback in the global climate system
• Albedo effect - Land once
covered by highly reflective
ice/snow is now exposed
• In a warmer world
evaporation of sea water
more water vapour in
atmosphere warming
• BUT Warmer world more
clouds, thus reduced solar
radiation at surface.
However, high clouds exert
blanketing effect and warm
the system
13. Complexity of global climate
system
• Climate is complex
– Atmosphere constantly changing
– Land surface variable in time and space
– Ocean currents, polar ice extent, nutrients in oceans
affecting productivity and atm. CO2
• Some changes predictable eg. earth’s orbital
pattern controlling diurnal and seasonal effects
as well as longer term tilt of earth axis
responsible for ice ages
• All compounded by Feedback Effects
14. The Greenhouse Effect: natural
and enhanced
• Earth temp. controlled by energy from sun
and reflection of some of this back to space
• Approx 1/3 solar energy reflected back,
most absorbed by land and oceans
• When earth warm, emits long wave
infrared radiation, trapped by greenhouse
gases
• Some gases critical to this balance (Maslan Table 1)
• Without this, earth 35º cooler
15. Greenhouse effect
Glass of greenhouse actually prevents air movement which allows cooling, so
LWR reabsorbed
18. Enhanced Greenhouse Effect
• Evidence CO2 linked to earth
temperature from air bubbles in ice
cores in Greenland and Arctic
• Last 2.5m years earth climate cycled
between ice ages (ice 3km thick over
N. Hemisphere above 50deg Lat.), to
conditions warmer than today
• Found CO2 and methane co-vary
with temperature over last 605k years
• Suggests that when CO2 and C4
increase, so does temperature, and
vice/versa
• This of great concern for future
climate
• Major worry: past climate has varied
by up to 5ºC in a few decades,
suggesting that climate follows a non-
linear path
Figure 2. Maslan
Four glacial cycles recorded
In Vostok ice core
Maslan Ch. 1
19. Current knowledge and uncertainties
• G. gas concentrations in atmosphere rising since
industrial revolution (fact)
• G. gases in atmosphere do cause global temperature
change, BUT how does climate system respond to inc.
CO2
?
• Many impacts of warmer atmosphere –
– Regional temperature changes
– Melting glaciers and ice sheets
– Relative sea level change
– Precipitation changes
– Storm intensity and tracks
– El Nino and ocean circulation changes
– (all of these have different response times)
• On top of all this, natural cyclical forcing – sun spots and
ice ages
20. What is the IPCC?
Established in 1988 by WMO due to worries about
possible global warming
Role: continued assessment of state of knowledge
(not do research)
Major influence on the UN Framework
Commission on Climate Change (UNFCC) and its
Kyoto Protocol in 1998 (the most far-reaching
global environmental treaty ever)
Second attempts in The Hague 2000 and Bonn
2001
USA pulled out in 2001, but Kyoto Protocol finally
came into force in 2005 with 55 countries
representing 55% of global emissions signed up
By 2008 178/192 countries recognised by UN
signed- all major countries except USA
21. Signatories to Koto Protocol in 2011
Dark Green – signed and ratified (agreed to cap emissions in accordance with
protocol) ie. most countries, 8% reduction compared to 1990 levels by 2012,
Green – Developing countries signed but without targets
Brown- signed but not intending to ratify
Dark brown - withdrawn
Grey- undecided
