How it all fits together Electromagnetic waves Atoms Heat
Electricity
Slide 6
How it all fits together
Slide 7
Global Warming The problem with this problem
Slide 8
This evening Do you have any personal evidence that the climate
is changing? What do we mean by climate?
Slide 9
What do we mean by Climate? What is the Climate? Its the
average weather in a particular area What is the Climate? Its 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.
Slide 10
This evening Why is the Earth the temperature it is? The Earths
Atmosphere Carbon dioxide Why are scientists concerned? Whats going
to happen? What should we do? Wed like you to do this!
Slide 11
The Simple Story What determines the surface temperature of the
Earth? Energy Balance
Slide 12
A Question? How hot does an object get hot when placed in front
of a fire?
Slide 13
What determines the surface temperature of the Earth? Simple
Story (1) Light from the Sun heats the Earth The Sun Earth 6400
C
Slide 14
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)
Slide 15
What determines the surface temperature of the Earth? Simple
Story (3) Light from the Sun heats the Earth The Earth then
radiates heat away Light from the Sun Earth
Slide 16
What determines the surface temperature of the Earth? Simple
Story (4) heat input from the Sun heat lost from the Earth by
radiation When there is balance, the Earths average temperature
will be stable Earth Warms Earth Cools
Slide 17
What determines the surface temperature of the Earth? The
Energy Balance of the Earth
Slide 18
Earth Warms Earth Cools What determines the surface temperature
of the Earth? The Numbers World Energy Production heat input from
the Sun heat lost from the Earth CO2 emissions
Slide 19
What determines the surface temperature of the Earth? Some more
details
Slide 20
What determines the surface temperature of the Earth? More
detail (1) We need to know: How much light reaches the Earth? How
much light reaches the Earths Surface? How much energy is radiated
from the Earths Surface?
Slide 21
What determines the surface temperature of the Earth? How much
light reaches the Earth? Light from the Sun heats the Earth Earth
At the top of the atmosphere Above the Equator At midday About 1360
W/m 2
Slide 22
What determines the surface temperature of the Earth? How much
light reaches the Earth? Light from the Sun heats the Earth Earth
North Pole South Pole Equator 1360 W/m 2 680 Whole Earth Average
340 W/m 2
Slide 23
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
Slide 24
What determines the surface temperature of the Earth? Hold on a
moment! What about all the heat rising up from the Earths hot
centre?
Slide 25
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 Earths surface Heat flow to and from surface from the Sun
240 Watt per Square metre
Slide 26
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!
Slide 27
1. What determines the surface temperature of the Earth? More
detail (2) Infra Red Radiation cools the Earth Light from the Sun
heats the Earth
Slide 28
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
Slide 29
1. What determines the surface temperature of the Earth? More
detail (2) How hot must the Earth be to radiate 240 W/m 2 ? Average
Value 240 watts per square metre -18 C
Slide 30
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
Slide 31
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
Slide 32
1. What determines the surface temperature of the Earth? More
detail (4) -18 C Average Surface Temperature 33 C Temperature for
radiation balance +15 C Greenhouse Effect
Slide 33
What determines the surface temperature of the Earth? The
Earths surface is 33 C warmer than it would be if had no
atmosphere
Slide 34
The Atmosphere Earths Atmosphere the Greenhouse Effect
Slide 35
The Atmosphere More detail (5) What is the composition of the
atmosphere? Gas% Nitrogen (N 2 )78.1 Oxygen (O 2 )20.1 Argon
(Ar)0.93 Water (H 2 O)0.1 to 1 Carbon Dioxide (CO 2 )0.035
Slide 36
Illustration of atmospheric composition More detail (6) About
100 molecules O2O2 Ar N2N2
Slide 37
Illustration of atmospheric composition More detail (7) About
1200 molecules Water(H 2 O)
Slide 38
Illustration of atmospheric composition More detail (8) About
10000 molecules Carbon dioxide (CO 2 )
Slide 39
The Atmosphere More detail (9) Nitrogen (N 2 ), Oxygen (O 2 )
& Argon (Ar) > 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
Slide 40
The Atmosphere More detail (10) 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
Slide 41
The Atmosphere More detail (10) Greenhouse warming is caused by
Water (H 2 O) Carbon Dioxide (CO 2 )
Slide 42
The Atmosphere More detail (11) What is special about H 2 O and
CO 2 ? Molecules have three atoms Natural frequencies of vibration
in the infra-red They make the atmosphere opaque to certain
infra-red frequencies
Slide 43
The Atmosphere More detail (12) Absorbtion frequencies
determined by exact frequencies of molecular jiggling
Slide 44
The Atmosphere and the Greenhouse Effect The Transparency of
the Atmosphere
Slide 45
Warning! Complicated diagram !
Slide 46
Infra RedUltra VioletVisible Absorption bands
Slide 47
1. What determines the surface temperature of the Earth? More
detail (2) Infra Red Radiation cools the Earth
Slide 48
What determines the surface temperature of the Earth? More
detail (16) In balance at + 15 C On Average 240 W/m 2 On Average
390 W/m 2 150 W/m 2 sent back to Earth Average Value 240 W/m 2
