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					                     Climate Science
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                                                       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:         Very thin
  Mean temperature:   –65oC
The Big Picture
  MARS:
  Atmosphere:         Very thin CO2
  Mean temperature:   –65oC (but –140oC to +20oC )
                      No significant greenhouse effect
The Big Picture
  VENUS:
  Atmosphere:         Thick
  Mean temperature:   +464oC
The Big Picture
  VENUS:
  Atmosphere:         Thick CO2!
  Mean temperature:   +464oC
                      A runaway greenhouse effect!
The Big Picture
   EARTH:
   Atmosphere:         N2 , O2 , H2O and a little CO2
   Mean temperature:   +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



Stefan-
Boltzmann
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 CO 2 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
CO 2 it could raise
the temperature by
about 5 degrees!”



 That‟s will that far
 “Thatnot all make
 Sweden warmer
 off modern 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       UV

    Infrared                  Ultraviolet
  1 µm         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 pre-
industrial
times


This is the
problem       IPCC 2007
                                                                           233



                     342
                    -107
                    =235
                                                                              326




The problem is that the added CO 2 has increased the 324 back radiation by ~2 W/m 2.
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

                                                 324
                                 350             326
                      Other



                                                 Back
                                Radiation       Radiation

Earth must warm in order to increase outgoing 233 back to 235
                                      233
                                      235

         235

                       +1            +5              326
                                   350               330
                        Other



                                   355               Back +4
                                  Radiation         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 1/2000 th!)
 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                                 Long wavelength
0.1 µm             (µm = millionth of a metre)           100 µm



                                                   Absorbed
                                                   mostly
                                                   by CO2
                Climate science
Absorption spectra for greenhouse gases




                            H2O           CO2


                              CH4
              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     1995
  better computers.
 Initial conditions are
  put in and then...
 mass (wind) and
                           2001
  energy (heat) transfer
  between cells is
  calculated...
 and recalculated
  billions of times!       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

 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 says it is...
              Climate science

 Certainly the temperature is dependent on
  many other factors AS WELL...
 ... (why don‟t deniers understand that?)
 The sun cycles...
              Climate science

 Certainly the temperature is dependent on
  many other factors AS WELL...
 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 more
  than the warming!
            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

				
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