Protons for Breakfast
Week 4:
Global Warming
In the event of an alarm
sounding…
Global Warming
Can we collect your facts please…
How it all fits together…
Electricity
Electromagnetic
waves
Atoms
Heat
How it all fits together…
This evening…
Do you have any personal evidence
that the climate is changing?
What do we mean by ‘climate?’
What do we mean by Climate?
What is the Climate?
It’s the average weather
in a particular area
What is the Climate?
It’s the average weather
Over a period a time (30 years usually)
Averages of temperatures and rain occurrence
Calculated scientifically
Things like that determine what we call the Climate
Determine what the climate of a place will be.
This evening…
• Why is the Earth the temperature it is?
• The Earth’s Atmosphere
• Carbon dioxide
• Why are scientists concerned?
• What’s going to happen?
• What should
we do?
– We’d like you
to do this!
The Simple Story
What determines the surface temperature of the Earth?
Energy Balance
A Question?
How hot does an object get hot when placed in front of a fire?
What determines the surface
temperature of the Earth?
Simple Story (1)
Light from the Sun heats the Earth…
The Sun
Earth
6400 °C
What determines the surface
temperature of the Earth?
Simple Story (2)
Drawn to Scale…
The Sun
Earth
(drawn 100 times
too big)
(drawn to scale)
What determines the surface
temperature of the Earth?
Simple Story (3)
Light from the Sun heats the Earth…
Light from
the Sun
Earth
The Earth then radiates heat away…
What determines the surface
temperature of the Earth?
Simple Story (4)
heat input from
the Sun
heat lost from
the Earth by
radiation
Earth
Warms
Earth
Cools
When there is balance, the Earth’s average
temperature will be stable
What determines the surface
temperature of the Earth?
The Energy Balance of the Earth
What determines the surface
temperature of the Earth?
The Numbers
heat input
from the
Sun
CO2
emissions
heat lost
from the
Earth
Earth
Warms
World Energy
Production
Earth
Cools
What determines the surface
temperature of the Earth?
Some more details…
What determines the surface
temperature of the Earth?
How much light reaches
the Earth?
•At the top of the atmosphere
•Above the Equator
•At midday
•About 1360 W/m2
Earth
What determines the surface
temperature of the Earth?
How much light reaches
the Earth?
Earth
680
North Pole
1360 W/m2
Equator
Whole Earth Average 340 W/m2
South Pole
What determines the surface
temperature of the Earth?
More detail (1)
Light reflected from Earth
Average Value
100 watts per square metre
Light from the Sun
Average Value
340 watts
per square metre
What determines the surface
temperature of the Earth?
Hold on a moment!
What about all the heat rising up
from the Earth’s hot centre?
Earth
Temperature increases by ~20 °C
for each kilometre below the
Earth’s surface
Heat flow is less than
0.1 Watt per square
metre
5500 °C
6400 km radius
Heat flow to and from
surface from the Sun
240 Watt per Square
metre
What determines the surface
temperature of the Earth?
A remarkable fact…
Heat flow from the centre of the Earth can be
completely ignored when considering what
determines the surface temperature of the Earth!
1. What determines the surface
temperature of the Earth?
More detail (2)
Light from the Sun heats the Earth…
Infra Red Radiation cools the Earth…
1. What determines the surface
temperature of the Earth?
More detail (2)
Light from the Sun heats the Earth…
Average Value
240 watts
per square metre
Average Value
240 watts per square
metre
1. What determines the surface
temperature of the Earth?
More detail (2)
How hot must the Earth be to radiate 240 W/m2 ?
Average Value
240 watts per square
metre
-18 °C
A Question
What is the average temperature of the Earth?
1 metre above the surface and averaged over:
• day and night,
• all latitudes and longitudes.
• all seasons
(a) – 15 ° C
(b) – 5 ° C
(c) + 5 ° C
(d) + 15 °C
A Question and an Answer
What is the average temperature of the Earth?
1 metre above the surface and averaged over:
• day and night,
• all latitudes and longitudes.
• all seasons
(a) – 15 ° C
(b) – 5 ° C
(c) + 5 ° C
(d) + 15 °C
1. What determines the surface
temperature of the Earth?
More detail (4)
Average
Surface
Temperature
+15 °C
Greenhouse
Effect
33 °C
Temperature
for radiation
balance
-18 °C
What determines the surface
temperature of the Earth?
The Earth’s surface is 33 °C warmer
than it would be if had no atmosphere
The Atmosphere
Earth’s Atmosphere
the Greenhouse Effect
The Atmosphere
More detail (5)
What is the composition of the atmosphere?
Gas
%
60
Nitrogen (N2)
78.1
50
Oxygen (O2)
Nitrogen
20.1
80
70
40
30
20
Argon (Ar)
Water (H2O)
Oxygen
Argon
0.93
Water
Carbon
Dioxide
0.1 to
1
10
0
Carbon Dioxide (CO2)
Fraction
0.035
Illustration of atmospheric
composition
More detail (6)
O2
N2
About 100 molecules
Ar
Illustration of atmospheric
composition
More detail (7)
About 1200 molecules
Water(H2O)
Illustration of atmospheric
composition
More detail (8)
About 10000 molecules
Carbon dioxide (CO2)
The Atmosphere
More detail (10)
Greenhouse warming is caused by
Water (H2O)
Carbon Dioxide (CO2)
The Atmosphere
More detail (11)
What is special about H2O and CO2?
• Molecules have three atoms
• Natural frequencies of vibration in the infra-red
• They make the atmosphere opaque to certain
infra-red frequencies
The Atmosphere
More detail (12)
• Absorbtion frequencies determined by exact
frequencies of molecular jiggling
The Atmosphere and the
Greenhouse Effect
The Transparency of the Atmosphere
Warning!
Complicated diagram
!
Absorption bands
Ultra Violet
Visible
SUN
6400 °C
(left-hand scale)
Infra Red
1. What determines the surface
temperature of the Earth?
More detail (2)
Infra Red Radiation cools the Earth…
What determines the surface
temperature of the Earth?
More detail (16)
• In balance at + 15 °C…
Average Value
240 W/m2
On Average
240 W/m2
150 W/m2
sent back to
Earth
On Average
390 W/m2
Greenhouse Warming
Others <1 °C
CO2 2 °C
33 °C
H2O 31 °C
A Question
If H2O is a
more important
greenhouse gas
than CO2,
why aren’t we
worried about
water vapour
emissions?
Answer
Residence time
Excess H2O in the atmosphere
• causes rain within a few days
Excess CO2 in the atmosphere
• takes a few hundred years to remove
Photo Credit
http://www.cepolina.com
How the parts fit together
Greenhouse Effect
Atmospheric
Water
Clouds
Global
Temperature
Evaporation
Carbon
Dioxide
Small slowly changing
contribution to
Greenhouse Effect
Experiment
Does water block infrared light?
Water Absorption bands
Ultra Violet
Visible
SUN
6400 °C
(left-hand scale)
Infra Red
HEATER
1000 °C
Greenhouse Effect
• Earth’s surface is warmed by the Greenhouse Effect
• Caused by water and carbon dioxide
• Turns the Earth from a ‘snowball’ with a hot Equator
into the relatively temperate place
So what’s the problem?
Carbon dioxide &
the carbon cycle
The amount of carbon dioxide in
the Earth’s atmosphere is increasing…
Atmospheric CO2 Concentration
versus year
Current value
388 ppm
400
2
CO Concentration (PPM)
350
300
250
200
150
100
parts per
million
Historical Value
280 ppm
50
0
1700
1750
1800
1850
Year
1900
1950
2000
Atmospheric CO2 Concentration
versus year
(Detail 2)
400
2
CO (ppm)
380
360
340
320
300
1960
1970
1980 1990 2000 2010
Click Graph to link to NOAA
Web Site for Latest Data
Year
Carbon dioxide
Why is the amount of carbon dioxide in
the Earth’s atmosphere is increasing?
• We are digging up geological deposits of carbon
– Coal & Oil & Gas
• We are burning them!
C + O2 →CO2
Michael’s family
CO2 emissions
0.2 kg per
mile
4000
miles per year
800 kg
CO2/year
0.3 kg per
Holiday in
mile per
California!
person
56000
1000
person
miles
per
miles!
year
600 kg
16,000
kg
CO22/year
0.5 kg per
kWh
0.2 kg per
kWh
7300
kWh per
year
17000
kWh per
year
3650 kg
CO2/year
3400 kg
CO2/year
My family’s CO2 emissions
8500 kg of CO2 per year at home
16000 kg For our holiday in California!
24.5 tonnes!!
There are many families like Michael’s…
Global CO2 Emissions
10.0
30 billion tonnes CO2
30
8 billion tonnes C
6.0
25
EVERY YEAR
20
15
4.0
10
2.0
5
0.0
1750
0
1800
1850
1900
Year
1950
2000
Billions of Tonnes of
Carbon Dioxide
Billions of Tonnes of
Carbon
8.0
35
Question
Is 8 billion tonnes of carbon per year
(emitted as CO2)
a lot or a little?
Carbon Cycle
(Amounts of
carbon in
billions of tons)
760 increasing
760 at 3.2/year
6.4
60
90
1.4
500
2,000
300
3,000
1.7
1,000
39,000
Cause for Concern?
What is the effect of increased levels of
carbon dioxide in the Earth’s atmosphere?
Nobody knows
Climate Models
What is the current effect
of CO2
• A net extra ‘forcing’ of around 2 watts per square metre…
Average
240 W/m2
Average
240 W/m2
150 W/m2
+ 2 W/m2
On Average
390 W/m2
Cause for Concern?
Should we be concerned?
Cause for Concern?
Scientists are concerned for several reasons:
1. Pre-historic studies show a correlation
between atmospheric CO2 levels and global
climate
2. There are observed changes in climate
Cause for Concern?
1 year of snow
From
approximately
16,250 years ago
Prehistoric Studies
Pre-Historic studies
Bubbles in Arctic and Antarctic
Ice
180 ppm Minimum
Carbon Dioxide
Concentration (PPM)
400
300 ppm Maximum
300
200
100
Ice Ages
0
800
600
400
200
Thousands of years before present day
0
Milankovitch Cycles
Did CO2 cause the ice ages?
No, CO2 helped us escape from them!
Ice ages are caused by
small changes in the orbit of
Earth around the Sun
Milankovitch Cycles
Pre-Historic studies
Bubbles in Arctic and Antarctic
Ice
Current value
388 ppm
Carbon Dioxide
Concentration (PPM)
400
300
200
100
Range of variation in
last 800,000 years
0
800
600
400
200
Thousands of years before present day
0
Cause for Concern?
Observed Changes in Climate
Observed Changes
Average surface temperature is difficult to measure
Observed changes
It is difficult to detect small
changes in a long series of
data?
My Weight: Spotting a trend
2008-2009
86.0
85.0
84.0
83.0
Weight (kg)
82.0
81.0
80.0
79.0
78.0
77.0
76.0
75.0
0
10
20
30
40
50
Days of Dieting
60
70
80
90
10
Observed changes
Best estimates
1
Temperature Anomaly (Celsius)
0.8
0.6
0.4
But its not just average
temperature that matters
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
1850
1870
1890
1910
1930
1950
1970
1990
Year
http://www.cru.uea.ac.uk/cru/climon/data/themi/g17.dat
2010
Other observations
Germany
Other observations
Photo credit:
Global Warming Art
Muir Glacier, Alaska
Other observations
Argentina
Causes for concern
•
•
Pre-historic climate studies
Observed changes
A Question
Can we be completely sure that the
climate changes we observe are caused by
anthropogenic emissions of carbon dioxide?
Man-made
and
Woman-made
2007:
2001:
It is
It very
is likely
likely
The Future…
CO2 levels will continue to rise…
• If we make a 50% cut in global emissions…
– This is a very optimistic assumption
– Requires a much greater cut (80% ?) by the UK
• …then CO2 will stabilise at twice historical levels
– Probably the best we can hope realistically hope for.
What could we do?
What should we do?
• Nothing
– Spend money on coping with consequences
• We could reduce the amount of CO2 we emit
– Even though this involves saving energy, this still costs money
– Things we do now will cost us money now
• Is global warming our top priority?
– Global poverty? AIDS?
– Hospitals? Education? Science? Banks?
• Would you vote to increase the price of all fuels?
So…
What do YOU think we should do?
Despair?
You may never know what results
come of your action,
but if you do nothing,
there will be no result.
Mahatma Ghandi
Goodnight
See you next week
to discuss…
Mobile Phone
Safety!
Unused Slides
Contributions to
Climate Forcing
Climate Forcing (W/m2)
-1
0
+1
Carbon Dioxide
Methane
Greenhouse
gases
Chlorofluorocarbons
Nitrous Oxide
Ozone
Black Carbon
Aerosols
Reflective aerosols
Cloud droplet changes
Land cover changes
Sun
Feedback
Increased
Climate
Forcing
Increased
Water
Vapour
Positive
Climate
Forcing
Global
Temperature
Negative
Decreased
Climate
Forcing
Increased
Cloud
Cover
More
Evaporation
Powers of Ten (Global Warming)
Length scale in metres
Microbes
Human
Relationships
10-18 10-12 10-6 100
Very
Very
Small 10-15 10-9
Atoms &
Molecules
Diameter
of the
Earth
Distance
to the
Sun
106 1012 1018 1024 1030 1036
10-3 103
109 1015 1021 1027 1033
Tallest
Mountain
Deepest
Trench
Very
Very
Large
The phenomenon of
global warming
involves physical processes
with length scales
spanning 20 powers of 10!
The spectrum of sunlight
http://cdiac.ornl.gov/trends/emis/em_cont.htm
10
Billions of tonnes of Carbon
Global
CO2
Emissions
8
Total Global
CO Emissions
?
2
6
Developed Countries
4
2
0
1990
Developing Countries
1995
2000
2005
2010
IPCC
Predictions…
Climate Research Unit East Anglia University
1 metre
2008
0.5 metres in
100 years ?
IPCC
Predictions…
1 metre
in 100 years
http://en.wikipedia.org/wiki/Sea_level_rise
http://cdiac.ornl.gov/trends/emis/tre_uki.htm
0.200
Total
UK Emissions
Billions of Tonnes of Carbon
UK
CO2
Emissions
0.150
Coal
0.100
0.050
Petrol
&
Diesel
Gas
0.000
1750 1800 1850 1900 1950 2000 2050
Year
Earth Spins 365.25
times on its journey
around the Sun
Northern
Hemisphere
Spring Equinox
Angle varies from
22.5º to 24.5º
And back again every
40,000 years
Daily Rotation
Northern
Hemisphere
Summer
Northern
Hemisphere
Winter
23.5º tilt
Northern
Hemisphere
Autumn Equinox
Carbon dioxide
The amount of carbon dioxide in
the Earth’s atmosphere is increasing…
Historically
280 ppm
1950
310 ppm
2000
365 ppm
2025
about 425 ppm
2050
450-550 ppm
Cause for Concern?
Climate models
Climate Models
What is a computer model of the climate?
© Australian Bureau of Meteorology
Climate Models
What is the output of a climate model?
The Earth Orbits the Sun
Earth Spins 365.25
times on its journey
around the Sun
Angle varies from
22.5º to 24.5º
And back again every
40,000 years
Daily Rotation
Northern
Hemisphere
Summer
Northern
Hemisphere
Winter
23.5º tilt
Seasonal Changes in Ice Cover
Warmer ground emits trapped CO2 and Methane
This area used to reflect 90% of sunlight
Now it reflects only around 30%
If summer day length increases by a minute or two
or days are warmer on average by a small amount
IPCC Predictions…
Human
CO2
emissions
IPCC
Predictions…
Atmospheric
CO2
concentration
IPCC
Predictions…
Global Mean Temperature
We do nothing
We BEGIN to stop all emissions EVENTUALLY
We BEGIN to stop all emissions NOW
We stop all emissions NOW