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Climate Science
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This version 30 March 2010
Keith Burrows
Science Teachers for Climate Awareness
Climate Science
and why we need to know about it.
Download from www.vicphysics.org
The Big Picture
The Big Picture
MARS:
Atmosphere:
Mean temperature:
Very thin
–65oC
The Big Picture
MARS:
Atmosphere:
Mean temperature:
Very thin CO2
–65oC (but –140oC to +20oC )
No significant greenhouse effect
The Big Picture
VENUS:
Atmosphere:
Mean temperature:
Thick
+464oC
The Big Picture
VENUS:
Atmosphere:
Mean temperature:
Thick CO2!
+464oC
A runaway greenhouse effect!
The Big Picture
MOON:
Atmosphere:
Mean temperature:
None
–20oC
The Big Picture
EARTH:
Atmosphere:
Mean temperature:
N2 , O2 , H2O and a little CO2
+15oC
Just right!
Why?
Climate science
 Earth’s energy balance
– Average temperature of the Earth:
– Balance between incoming solar radiation
– and outgoing ‘heat’ radiation (IR)
Temperature is a balance between
heat in ... and heat out
Visible and Infrared (short wavelength)
Infrared (long wavelength)
Climate science
 Car temperature steady at 25°C
Visible in
25°C
IR out (same amount)
Climate science
 More heat in than out
– car warming 30°C
More visible in
30°C
IR out increasing
(but less than in)
Climate science
 Heat in now same as heat out
– temperature steady 40°C
Visible in
40°C
IR out increased
– now same as in
Climate science
 As things getter hotter they:
 1) Radiate more energy (as with the car)
 2) Get brighter and bluer
(infrared → red → yellow → white → blue)
We see the kettle by
reflected light – we can’t see
the IR. But we can feel it.
Climate science
 Heat in now same as heat out
– temperature steady 40°C
Climate science
Earth’s energy balance
So what determines the Earth’s temperature?
 The balance between the energy coming in
 ... and that going out.
So what determines the Earth’s temperature?
 Both incoming and outgoing energy radiation can
vary over long time intervals.
 Or even quite short ones!
So what determines the Earth’s temperature?
 That is what leads to CLIMATE CHANGE
So what determines the Earth’s temperature?
 Incoming sunlight varies with...
The Sun in
UV light
So what determines the Earth’s temperature?
 Incoming sunlight varies with...
So what determines the Earth’s temperature?
 Incoming sunlight varies with...
~30%
90%+
So what determines the Earth’s temperature?
 Incoming sunlight also varies with...
So what determines the Earth’s temperature?
 Outgoing energy varies with...
1) How
hot the
Earth is
and...
So what determines the Earth’s temperature?
2) ...how much energy is trapped by the atmosphere
A little physics
 Earth’s energy balance
– Two simple laws of physics
enable us to figure out the
energy balance:
 The Stefan-Boltzmann law...
I = εσT4
 Wien’s law... λmax = 0.0029/T
– S-B just tells us how much
heat a hot object radiates.
– Wien tells us what sort of
radiation it will be.
(but fortunately others have done the
hard work for us!)
A little physics
StefanBoltzmann
is about
intensity
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“The Earth’s
average
temperature
should be about
–18oC”
?
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“Ah! The
atmosphere
must be
trapping the
heat”
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“But Oxygen
and Nitrogen
can’t absorb the
infrared
radiation”
?
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“It must be the
water vapour
and carbon
dioxide!”
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“Together they
absorb heat and
re-emit enough
back to Earth to
raise the
temperature by
+33degrees!”
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“So what will all
the CO2 we are
putting in the
atmosphere do?”
?
Climate science
 Earth’s energy balance
 Svante August Arrhenius worked it out in 1896
“If we double the
CO2 it could raise
the temperature by
about 5 degrees!”
“That
will
That’s not
all make
that far
Sweden
off modernwarmer
estimates
– good
IPCC:
2°C !”
→ 5°C
Climate science
 Earth’s energy balance (sum up)
– The average temperature of the Earth is
determined by the balance between incoming
solar radiation and outgoing ‘heat’ radiation
– Not all the IR radiation from the surface
escapes immediately...
– or the average temperature would be a
freezing –18ºC
– No liquid water or clouds
– And no life!
Climate science
 Why do water vapour (H2O) and
carbon dioxide (CO2) molecules
‘trap’ heat radiation...
... when 99% of the atmosphere
(nitrogen and oxygen) just lets it
all through?
A little more physics!
 ‘Light’ can be ultraviolet (UV), visible, or
infrared (IR). It is measured by ‘wavelength’.
IR
R O Y G B V
Infrared
1 µm
UV
Ultraviolet
0.7 µm
0.4 µm
0.1 µm
1 µm = 1 thousandth of a millimetre
A little more physics!
 But light also comes as ‘photons’
Here’s a visible light one:
... but light never ‘stops’!
It either travels at ‘the speed of light’ or it is
absorbed as energy.
A little more physics!
 Here’s an infrared one:
 Notice that it has a longer wavelength
 (And of course they don’t really look like this!)
Back to climate science
 How do those air molecules ‘trap’ the IR
photons?
Oxygen (O2)
Water vapour (H2O)
Nitrogen (N2)
Of course molecules
don’t ‘look’ like this either!
Carbon dioxide (CO2)
Climate
science
^
 Nitrogen and oxygen molecules:
 Two atoms ‘tightly bound’
Climate
science
^
 Water and carbon dioxide molecules:
 Three atoms ‘loosely bound’
Climate
science
^
 Nitrogen and oxygen molecules:
 Light ‘photons’ (visible and IR) go right
through N2 and O2
Climate
science
^
 Water and carbon dioxide molecules:
 Infrared photons get absorbed by H2O and
CO2 molecules (and give them energy)
Climate
science
^
 Water and carbon dioxide molecules:
 The H2O and CO2 don’t keep the energy...
 they ‘re-radiate’ it.
Climate science
 Some of this re-radiated IR goes back down
and warms the surface – a little like a
greenhouse...
 The so called “Greenhouse Effect”
 This keeps the Earth at a warm +15oC
(average) instead of that freezing –18oC
More complex climate science
 This is where things get a bit more
complicated!
 There are
More complex climate science
 Clouds are a problem! For a start...

Climate science
 They reflect light back to space
 (negative feedback)
 But also reflect IR back to the surface
 (positive feedback)
Climate science
 High clouds act differently to low clouds
And there are aircraft contrails to be taken into account
Climate science










As well, there are:
Volcanos
Vegetation changes
Aerosols
Heat exchange - ocean and air (ENSO)
Ice and snow coming/going
Glaciers changing
Changes in weather patterns
... and lots more
... including human added CO2!
IPCC
NOW
~390
CO2 has probably not been this high for several million years
Climate science
 So what are we actually doing to the
atmosphere and why does it matter?
 (It’s not only carbon dioxide)
IPCC
(IPCC graph)
The basic data needed is measured in various ways and is well known.
Notice that overall, incoming equals outgoing (342 = 107 + 235). Also, that
large amounts of energy are absorbed and re-radiated by greenhouse gases.
342
-107
=235
Let’s combine the incoming solar and reflected solar - leaves net of 235 incoming
That’s equal to the total outgoing IR radiation.
Or was before we came along!
These are
the changes
in the
forcing
since preindustrial
times
This is the
problem
IPCC 2007
233
342
-107
=235
326
The problem is that the added CO2 has increased the 324 back radiation by ~2 W/m2.
and therefore decreased the 235 outgoing by ~2 W/m2.
The Earth is no longer in balance. Let’s make a simpler picture!
235
233
235
Other
350
Radiation
324
326
Back
Radiation
Earth must warm in order to increase outgoing 233 back to 235
233
235
235
Other
+1
+5
350
355
Radiation
326
330
Back +4
Radiation
This increases radiation AND Back Radiation until total increases
by 2
Climate science
 Typical denier statement:
 “…the idiotic notion that
increasing by less than
1/2000 this century the
proportion of the Earth’s
atmosphere occupied by
CO2 may prove
catastrophic.”
 “The Viscount Monckton of
Brenchley” in a letter to Kevin
Rudd 1 January 2010
Climate science





1/2000th ?
Pre industrial CO2: 280 ppm =0.028%
≈ 3/10,000
Now:
390 ppm = 0.039%
≈ 4/10,000 So the increase so far has been ≈
1/10,000 (well yes, it is less than 1/2000th!)
 These calculations are irrelevant!
 280 ppm 390 ppm is a 39% increase
 3/10,000 4/10,000 is a 33% increase
Climate science
 This can only be seen as a deliberate
attempt to deceive by making the numbers
look small!
 Here is the effect of adding this ‘tiny
proportion’ (300 ppm) of ink to a glass of
water:
Climate science
 300 ppm (or 0.03%) might not sound like
much, but here is the effect of adding 300
ppm of ink to a glass of water:
Climate science
 Remember that the greenhouse effect keeps
the Earth at +15°C instead of –18°C
GHE
 We cannot expect that a 35% increase in CO2
a greenhouse gas won’t make a difference!
Note: Water vapour is the more important GHG, but the interaction between them is complex
Climate science
 Water vapour and carbon dioxide
 Deniers will claim that H2O is responsible for about
95% of the GHE
 This is false – It is not a ‘linear problem’
 H2O and CO2 act differently





Take away all H2O: Other GHGs absorb ~34%
Take away OGHGs: H2O absorbs ~85%
So effect of H2O ~ 66% – 85%
[100 – 34 = 66]
So effect of OGHGs ~ 15% – 34%
[100 – 85 = 15]
So CO2 on its own is 9% – 26% of the GHE
[As CO2 is about 60% of GHGs]
Climate science
 H2O is a feedback GHG, CO2 is a forcing GHG
– More CO2 → more warmth → more H2O
(evaporation) → more warmth → more H2O →
more warmth → ???
– But also, more water vapour → more clouds,
which...
– reflect sunlight, and reduce the warming effect.
– and which ...
Climate science
 reduce the amount of H2O in the atmosphere
 This is a Feedback effect
 Water vapour goes in and out of the atmosphere
very quickly
Climate science
Human added
H2O is not a
problem – it
soon rains out
again.
Climate science
– But CO2 is
another story!
Climate science
 Carbon dioxide molecules remain in the
air for ~ 100 years
 Methane for about 20 years
 There is NO FEEDBACK effect that gets
them out of the atmosphere
 That makes a very big difference in the
way they act.
 CO2 and CH4 (methane) are called
FORCING greenhouse gases
Climate science
 There is another important difference
between the three main greenhouse
gases.
 They absorb different parts of the IR
spectrum...
Climate
science
^
 H2O and CO2 molecules can take on the
energy in many different ways:
Climate
science
^
 Which means they absorb various different
types of infrared photons.
 (Light photons vary in their ‘wavelength’)
 Shorter wavelength
 Longer wavelength infrared
Climate science
 This means that they absorb different parts
of the IR radiation from the Earth’s surface.
Short wavelength
0.1 µm
(µm = millionth of a metre)
Long wavelength
100 µm
Absorbed
mostly
by CO2
Climate science
Absorption spectra for greenhouse gases
H2O
CH4
CO2
Climate science
 That means that even if the atmosphere is
saturated with water vapour a lot of IR still
gets through.
 CO2 and CH4 absorb IR wavelengths that
H2O doesn’t.
 (Many “sceptics” don’t seem to understand
that!)
Climate science
 The BIG QUESTIONS:
– If we continue to increase the greenhouse gases how
much will the temperature increase?
– Will that matter?
Climate science
 The BIG QUESTIONS:
– If we continue to increase the greenhouse gases how
much will the temperature increase?
– Will that matter?
 How can we find out?
– We need to use our understanding of the
science of climate change.
– This is done mostly by putting the data into
computer models and using the laws of physics.
Climate science
 To take all this into account scientists put all
the laws of physics and chemistry into
computer models which can do the vast
numbers of calculations needed.
 Some of the equations:
Climate science
 The models divide the atmosphere and
ocean into cells about 1 km deep
Climate science
 The cells have been
getting smaller with
better computers.
 Initial conditions are
put in and then...
 mass (wind) and
energy (heat) transfer
between cells is
calculated...
 and recalculated
billions of times!
1995
2001
2007
Climate science
 The models produce results rather like a
weather map, but over decades or centuries
Climate science
 The models are checked by putting in data
from long ago and ‘back forecasting’
Climate science
 Here are the results of a 150 year run:
Global
average
temperature
increase
Climate science
 But that was without human added CO2:
Global
average
temperature
increase
Climate science
 Here is the result with human added CO2:
Global
average
temperature
increase
Climate science
 The models correctly predict volcanic effects
Global
average
temperature
increase
1963 Agung
1982 El Chichon
1991 Pinatubo
Climate science
This is why scientists believe that
human added CO2 is
a problem!
 It is not just rising temperatures, melting ice,
more extremes etc.
Climate science
 Computer models are often criticised on the
basis of the bad performance of economic
models (the GFC!)
 Economic models:
 Human guesses about human behaviour !!!
 Climate models:
 The laws of physics and chemistry and
detailed observations.
Climate science
 We can also look at the past climate to
find clues about what can happen.
These temperatures are more approximate the further back in time we go.
“Climate change is natural” ... Yes but!
Climate science
 So is sea level change:
“Paul Blanchon's
team at the National
Autonomous
University of Mexico
in Cancun has been
studying 121,000
year old coral reefs in
the Yucatan
Peninsula, formed
during the last interglacial period when sea level peaked at around
6 metres higher than today. His findings suggest that at one point
the sea rose 3 metres within 50 to 100 years.”
Temperatures in that interglacial were only a couple of degrees warmer than the 20th C.
Climate science
Sea levels in
the last
interglacial
~120,000 ya
Maximum
temperature
~ 2°C warmer
10 m higher
Today
Climate science
Perhaps
even more
worrying?
...
18 February 2010
81,000 years ago sea levels
reached about 1 metre higher
than today...
NB This study still
awaits confirmation
from others
Climate science
 ... but temperatures were considerably
cooler than today.
Climate science
 Is it really CO2 though?
 The physics says it is.
 Geological history says it is...
Today
390
Climate science
 Is it really CO2 though?
 and the recent data is certainly consistent ...
Climate science
 Certainly the temperature is dependent on
many other factors AS WELL...
 ... (why don’t deniers understand that?)
 The sun cycles...
Climate science
 Other factors...
 And the ENSO (El Niño Southern Oscillation)
Very Large
El Niño 1998
La Niñas
Also note the drops
following volcanoes
 The annual variation is about
ten times the warming trend
 We see the weather
Climate science
 The effects of climate change are not
uniform warming.
 Some areas will warm faster and some very
slowly.
 Some will get wetter, some dryer
Average temperature increases for 2000 – 2009
compared to 1951 - 1980
Monthly average temperature increases for December
2009 compared to 1951 – 1980 Average global +0.62°C
Where the
‘skeptics’
are