4. 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.
5. One problem…
Do you have any personal evidence
that the global climate is changing?
6. 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?
8. How hot does an object get when
placed in front of a fire?
9. Light from the Sun heats the Earth…
The Sun
Earth
5400
°C
10. Light from the Sun heats the Earth…
Drawn to Scale…
The Sun Earth
(drawn 100 times
too big)
(drawn to scale)
11. Light from the Sun heats the Earth…
The Earth then radiates heat away…
Light from
the Sun
Earth
12. Energy Balance
heat input from
the Sun
heat lost from
the Earth by
radiation
When there is balance, the Earth’s average
temperature will be stable
Earth
Warms
Earth
Cools
16. How much light reaches the Earth?
Earth
•At the top of the atmosphere
•Above the Equator
•At midday
•About 1360 W/m2
17. How much light reaches the Earth?
Earth
North Pole
South Pole
Equator
1360 W/m2
680
Whole Earth Average 340 W/m2
18. 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
19. Hold on a moment!
What about all the
heat rising up
from the Earth’s hot
centre?
20. Earth
6400 km radius
5500 °C
Heat flow is less than
0.1 Watt per square
metre
Temperature increases by ~20 °C
for each kilometre below the
Earth’s surface
Heat flow to and from
surface from the Sun
240 Watt per Square
metre
21. 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!
22. What determines the surface
temperature of the Earth?
Infra Red Radiation cools the Earth…
Light from the Sun heats the Earth…
23. Radiation Balance
Light from the Sun heats the Earth…
Average Value
240 watts per square
metre
Average Value
240 watts
per square metre
24. Radiation Balance
How hot must the Earth be to radiate 240 W/m2 ?
Average Value
240 watts per square
metre
-18 °C
25. 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
28. 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?
29. 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
33. 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
34. 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
36. 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
37. Vibrations of CO2 and H20
• Different types of molecular jiggling occur at different frequencies
Water H20 Carbon dioxide C02
43. Radiation Balance in the 20th Century…
On Average
240 W/m2
On Average
390 W/m2
150 W/m2
sent back to
Earth
Average Value
240 W/m2
On Average
+ 15 ºC
44. Greenhouse Warming
33
°C
Others <1 °C
CO2 2 °C
H2O 31
°C
If H2O is a
more important
greenhouse gas
than CO2,
why aren’t we
worried about
water vapour
emissions?
45. Residence time
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
If H2O is a more important
greenhouse gas than CO2, why
aren’t we worried about
water vapour emissions?
46. How the parts fit together
Atmospheric
Water
Global
Temperature
Greenhouse Effect
Evaporation
Small slowly changing
contribution to
Greenhouse Effect
Clouds
Carbon
Dioxide
48. 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
49. 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?
50. 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?
51. 0
50
100
150
200
250
300
350
400
1700 1750 1800 1850 1900 1950 2000
CO
2
Concentration(PPM)
Year
Atmospheric CO2 Concentration
versus year
Historical Value
280 ppm
Current value
~390 ppm
parts per
million
Click for
latest value
52. 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
53. Michael’s family
CO2 emissions
0.2 kg per mile
4000
miles per year
800 kg CO2/year
0.3 kg per
mile per
person
1000
miles per year
600 kg
CO2/year
0.5 kg per
kWh
7300
kWh per year
3650 kg
CO2/year
Holiday in
California!
56000 person
miles!
8,000 kg
CO2/year
0.2 kg per
kWh
17000
kWh per year
3400 kg
CO2/year
54. 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…
58. Carbon Cycle
(Amounts of
carbon in
billions of tons)
760
908
2,000
39,000
500
1,000
3,000
(Coal)
300
(Oil &Gas)
2
2
760 increasing at 4 per year
60
59. Cause for Concern?
What is the effect of increased levels of
carbon dioxide in the Earth’s atmosphere?
Nobody knows
60. Radiation ‘Balance’ in 2012…
On Average
<240 W/m2
On Average
390 W/m2
150 W/m2
sent back to
Earth
Average Value
240 W/m2
On Average
+ 15 ºC
+2 W/m2
+?? ºC
62. 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?
63. 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
68. A Question?
Berkeley
NASA GISS
Hadley CRU
NOAA NCDC
What has happened?
What did Global Warming Theory predict in 1981?
http://berkeleyearth.org
But its not just average
temperature that matters
72. 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
2001: It is likely
2007: It is very likely
2013: It is very very likely
73. 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?
75. 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
76. IPCC Predictions… Global Mean Temperature
We stop all emissions NOW
We BEGIN to stop all emissions EVENTUALLY
We BEGIN to stop all emissions NOW
We do nothing
77. 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?
79. What could we do?
What should we do?
In smaller groups
• Please come up with some
questions, and suggestions
• We will gather these together and
then discuss them!
You decide!
80. Despair?
You may never know what results
come of your action,
but if you do nothing,
there will be no result.
Mahatma Ghandi