Protons for Breakfast
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
1800
1850
1900
1950
Global Warming
Week 4
2000
In the event of
of…
an attack of mutant bananas…
Global Warming
Can we collect your facts please…
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.
One problem…
Do you have any personal evidence
that the global climate is changing?
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
Energy Balance
How hot does an object get when
placed in front of a fire?
Light from the Sun heats the Earth…
The Sun
Earth
5400
°C
Light from the Sun heats the Earth…
Drawn to Scale…
The Sun
Earth
(drawn 100 times
too big)
(drawn to scale)
Light from the Sun heats the Earth…
Light from
the Sun
Earth
The Earth then radiates heat away…
Energy Balance
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
The Energy Balance of the Earth
Energy Balance: to scale
heat input
from the
Sun
heat lost
from the
Earth
Earth
Warms
World Energy
Production
Earth
Cools
Some more details…
How much light reaches the Earth?
•At the top of the atmosphere
•Above the Equator
•At midday
•About 1360 W/m2
Earth
How much light reaches the Earth?
Earth
680
North Pole
1360 W/m2
Equator
Whole Earth Average 340 W/m2
South Pole
How much light reaches the Earth’s Surface
Light reflected from Earth
Average Value
100 watts per square metre
Light from the Sun
Average Value
340 watts
per square metre
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
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!
What determines the surface
temperature of the Earth?
Light from the Sun heats the Earth…
Infra Red Radiation cools the Earth…
Radiation Balance
Light from the Sun heats the Earth…
Average Value
240 watts
per square metre
Average Value
240 watts per square
metre
Radiation Balance
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
Summary
Average
Surface
Temperature
Temperature
for radiation
balance
+15 °C
Greenhouse
Effect
33
°C
-18 °C
The Earth’s surface is 33 °C warmer
than it would be if had no atmosphere
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
The composition of the atmosphere?
Gas
%
Nitrogen (N2)
78.1
Oxygen (O2)
20.1
Argon (Ar)
0.93
Water (H2O)
0.1 to 1
Carbon Dioxide (CO2)
0.035
Illustration of atmospheric composition
O2
N2
About 100 molecules
Ar
Illustration of atmospheric composition
About 1200 molecules
Water(H2O)
Illustration of atmospheric composition
About 10000 molecules
Carbon dioxide (CO2)
Nitrogen (N2), Oxygen (O2) & Argon (Ar)
Suppose the atmosphere contained no carbon dioxide or water
• N2, O2 and Ar is more than 99% of the atmosphere
• Molecules have one or two atoms
• Natural frequency of vibration in the ultra-violet
• Make atmosphere opaque to ultra-violet light
• Transparent to infra-red and visible radiation
Nitrogen (N2), Oxygen (O2) & Argon (Ar)
With an atmosphere of only
Nitrogen Oxygen & Argon,
what would be the surface temperature?
Average Value
240 watts
per square metre
Average Value
240 watts per square
metre
-18 °C
Greenhouse warming is caused by
Water (H2O)
Carbon Dioxide (CO2)
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 infrared frequencies
Vibrations of CO2 and H20
• Different types of molecular jiggling occur at different frequencies
Water H20
Carbon dioxide C02
Absorption demo
Frequency
The Transparency of the Atmosphere
Warning!
Complicated diagram
!
Absorption bands
Ultra Violet
Visible
Infra Red
Infra Red Radiation cools the Earth…
Radiation Balance in the 20th Century…
On Average
240 W/m2
Average Value
240 W/m2
150 W/m2
sent back to
Earth
On Average
+ 15 ºC
On Average
390 W/m2
Greenhouse Warming
Others <1 °C
CO2 2 °C
33
°C
H2O 31
°C
If H2O is a
more important
greenhouse gas
than CO2,
why aren’t we
worried about
water vapour
emissions?
Residence time
If H2O is a more important
greenhouse gas than CO2, why
aren’t we worried about
water vapour emissions?
Because 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?
A Children’s song
What does the glass of a Greenhouse do?
It lets the short solar rays pass through
The objects in the house absorb these rays
And re-radiate them as long heat rays
What does the glass of a Greenhouse do?
It doesn’t let the long heat rays pass through
Trapped by the glass they bounce back and forth,
Re-radiated and re-absorbed
Stay Stay, you long heat rays, Warm up the house on cold cold days
Stay Stay, you long heat rays, Warm up the house on coooooold cold days
The atmosphere is like a greenhouse too
It lets most of the solar rays through
The surface of the Earth absorbs these rays
And re-radiates them as long heat rays
There’s vapour in the air, What does it do?
It doesn’t let the long heat rays pass through
Trapped by the vapour they bounce back and forth,
Re-radiated and re-absorbed
Stay Stay, you long heat rays, Warm up the house on cold cold days
Stay Stay, you long heat rays, Warm up the Earth on cooooooold cold days
Greenhouse Effect
• Earth’s surface is warmed by the Greenhouse Effect
• Caused by:
Water (mainly)
and carbon dioxide
• Turns the Earth from a ‘snowball’ with a hot Equator into the relatively
temperate place
So what’s the problem?
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
Atmospheric CO2 Concentration
versus year
Current value
~390 ppm
400
Click for
latest value
2
C O C o n ce n tra tio n (P P M )
350
300
250
200
150
100
parts per
million
Historical Value
280 ppm
50
0
1700
1750
1800
1850
Year
1900
1950
2000
Carbon dioxide
Why is the amount of carbon dioxide in
the Earth’s atmosphere is increasing?
• We are digging up carbon as:
Coal & Oil & Gas
• We are burning them!
C + O2 →CO2
Michael’s family
CO2 emissions
0.2 kg per mile
0.3 kg per
Holiday in
mile per
California!
person
0.5 kg per
kWh
0.2 kg per
kWh
4000
miles per year
56000
person
1000
miles!
miles
per year
7300
kWh per year
17000
kWh per year
800 kg CO2/year
600 kg
8,000
kg
CO22/year
/year
CO
3650 kg
CO2/year
3400 kg
CO2/year
My family’s CO2 emissions
8500 kg of CO2 per year at home
8000 kg For our holiday in California!
16.5 tonnes!!
There are many families like Michael’s…
Carbon?
Or Carbon dioxide?
1 tonne of CO2
CO2
0.27 tonne of C
0.73 tonne of O2
Global CO2 Emissions
1 0.0
35
30 billion tonnes CO2
30
8 billion tonnes C
25
6 .0
EVERY YEAR
20
15
4 .0
10
2 .0
5
0 .0
1 75 0
0
1 80 0
1 85 0
1 90 0
Y e ar
1 95 0
2 00 0
B illio n s o f T o n n e s o f
C a rb o n D io xid e
B illio n s o f T o n n e s o f
C a rb o n
8 .0
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)
760at 4 per year
760 increasing
8
60
90
2
500
2,000
300
(Oil &Gas)
3,000
(Coal)
2
1,000
39,000
Cause for Concern?
What is the effect of increased levels of
carbon dioxide in the Earth’s atmosphere?
Nobody knows
Radiation ‘Balance’ in 2012…
On Average
<240 W/m2
Average Value
240 W/m2
150 W/m2
sent back to
Earth
+?? ºC
On Average
+ 15 ºC
+2 W/m2
On Average
390 W/m2
Energy Balance: to scale
heat input
from the
Sun
heat lost
from the
Earth
Earth
Warms
Earth
Cools
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
4. Why are scientists are concerned
1. Pre-historic studies show a strong correlation
between atmospheric CO2 levels and global
climate.
2. There are observed changes in climate
1 year of snow
From approximately
16,250 years ago
Prehistoric Studies
Bubbles in Arctic and Antarctic Ice
180 ppm Minimum
395 ppm
C a rb o n D io x id e
C o n ce n tra tio n (P P M )
400
300 ppm Maximum
300
200
100
0
Ice Ages
800
600
400
2 00
T h o u sa n d s o f ye ars b e fo re p re s e n t d a y
0
Cause for Concern?
Observed Changes in Climate
One
estimate of the Land Surface Temperature?
A Question?
What
did Global Warming Theory predict in 1981?
A Question?
But its not just average
temperature that matters
B erkeley
N A S A G IS S
H a dley C R U
NOAA NCDC
http://berkeleyearth.org
What has happened?
Muir Glacier, Alaska
Glaciers
Glaciers are
retreating:
worldwide
Photo credit:
Global Warming Art
Arctic Sea Ice
http://nsidc.org/arcticseaicenews/
Arctic Sea Ice Minima
2013
2012
A Question
Can we be completely sure that the
climate changes we observe are caused by
anthropogenic emissions of carbon dioxide?
2001: It is likely
Man-made
and
Woman-made
2007: It is very likely
2013: It is very very likely
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
Climate Models
‘What’s going to happen?”
Nobody knows
• Climate Models ‘add up’
the many factors
The best ‘realistic’ possibility…
If we make a 50% cut in global emissions:
80% cut in the UK
CO2 concentraions will rise to
twice historical levels
and stabilise
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
This Evening…
1. Why is the Earth’s surface the temperature it is?
2. The Earth’s Atmosphere
3. Increasing Carbon Dioxide
4. Should we be concerned?
5. What’s going to happen?
6. What should we do?
What should we do…
Nothing
Something
Everything
What could we do?
What should we do?
You decide!
In smaller groups
• Please come up with some
questions, and suggestions
• We will gather these together and
then discuss them!
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!