Climate Science Keith Burrows Science Teachers for Climate Awareness This presentation is designed for teachers to use in schools or with their local community. This is a ‘lighter’ version than the original one posted on VicPhysics Newer versions of this presentation and others can be found at: Follow the link from the ‘Climate Change’ link on the ‘Home’ page. Be sure to look at the ‘Notes pages’ (below) for added comments to help in presenting and for more information and sources. Please feel free to me with suggestions for improvements or useful comments. The intention is that YOU SHOULD PICK AND CHOOSE FROM THESE SLIDES. THERE ARE REDUNDANT SLIDES – SOME PEOPLE WILL PREFER DIFFERENT APPROACHES.

Climate Science and why we need to know about it. Download from

The Big Picture

MARS: Atmosphere: Very thin Mean temperature: –65 o C

The Big Picture MARS: Atmosphere: Very thin CO 2 Mean temperature: –65 o C (but –140 o C to +20 o C ) No significant greenhouse effect

The Big Picture VENUS: Atmosphere: Thick Mean temperature: +464 o C

The Big Picture VENUS: Atmosphere: Thick CO 2 ! Mean temperature: +464 o C A runaway greenhouse effect!

The Big Picture EARTH: Atmosphere: N 2, O 2, H 2 O and a little CO 2 Mean temperature: +15 o C 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)

 Car temperature steady at 25°C 25°C Climate science Visible in IR out (same amount)

 More heat in than out – car warming 30°C 30°C Climate science IR out increasing (but less than in) More visible in

 Heat in now same as heat out – temperature steady 40°C – temperature steady 40°C 40°C Climate science IR out increased – now same as in Visible in

 As things getter hotter they:  1) Radiate more energy (as with the car)  2) Get brighter and bluer (infrared → red → yellow → white → blue) Climate science We see the kettle by reflected light – we can’t see the IR. But we can feel it.

 Heat in now same as heat out – temperature steady 40°C – 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 = εσT 4  Wien’s law... λ max = /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 –18 o C” ?

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 not all that far off modern estimates IPCC: 2°C → 5°C “That will make Sweden warmer – good !”

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!  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 (H 2 O) and carbon dioxide (CO 2 ) 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’. R O Y G B V IR 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? Nitrogen (N 2 ) Water vapour (H 2 O) Oxygen (O 2 ) Carbon dioxide (CO 2 ) Of course molecules don’t ‘look’ like this either!

Climate science  Nitrogen and oxygen molecules:  Two atoms ‘tightly bound’ Some simple ^

Climate science  Water and carbon dioxide molecules:  Three atoms ‘loosely bound’ Some simple ^

Climate science  Nitrogen and oxygen molecules:  Light ‘photons’ (visible and IR) go right through N 2 and O 2 Some simple ^

Climate science  Water and carbon dioxide molecules:  Infrared photons get absorbed by H 2 O and CO 2 molecules (and give them energy) Some simple ^

Climate science  Water and carbon dioxide molecules:  The H 2 O and CO 2 don’t keep the energy...  they ‘re-radiate’ it. Some simple ^

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 +15 o C (average) instead of that freezing –18 o C

More complex climate science

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 CO 2 !

IPCC

CO2 has probably not been this high for several million years NOW ~390

Climate science  So what are we actually doing to the atmosphere and why does it matter?  (It’s not only carbon dioxide)

IPCC

The basic data needed is measured in various ways and is well known. Notice that overall, incoming equals outgoing (342 = ). Also, that large amounts of energy are absorbed and re-radiated by greenhouse gases. (IPCC graph)

Let’s combine the incoming solar and reflected solar - leaves net of 235 incoming =235 That’s equal to the total outgoing IR radiation. Or was before we came along!

IPCC 2007 These are the changes in the forcing since pre- industrial times This is the problem

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/m =235 The Earth is no longer in balance. Let’s make a simpler picture!

Back BackRadiation Radiation Other Earth must warm in order to increase outgoing 233 back to 235

Back BackRadiation Radiation Other This increases radiation AND Back Radiation until total increases by

Climate science TTT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

 1/2000 th ?  Pre industrial CO 2 : 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  We cannot expect that a 35% increase in CO 2 a greenhouse gas won’t make a difference! GHE 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 H 2 O is responsible for about 95% of the GHE  This is false – It is not a ‘linear problem’  H 2 O and CO 2 act differently   Take away all H 2 O: Other GHGs absorb ~34%   Take away OGHGs: H 2 O absorbs ~85%   So effect of H 2 O ~ 66% – 85% [100 – 34 = 66]   So effect of OGHGs ~ 15% – 34% [100 – 85 = 15]   So CO 2 on its own is 9% – 26% of the GHE [As CO2 is about 60% of GHGs]

Climate science  H 2 O is a feedback GHG, CO 2 is a forcing GHG –More CO 2 → more warmth → more H 2 O (evaporation) → more warmth → more H 2 O → 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 H 2 O in the atmosphere  This is a Feedback effect  Water vapour goes in and out of the atmosphere very quickly

Climate science Human added H 2 O is not a problem – it soon rains out again.

Climate science –But CO 2 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.  CO 2 and CH 4 (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  H 2 O and CO 2 molecules can take on the energy in many different ways: More simple ^

Climate science  Which means they absorb various different types of infrared photons.  (Light photons vary in their ‘wavelength’)  Shorter wavelength  Longer wavelength infrared More simple ^

Climate science  This means that they absorb different parts of the IR radiation from the Earth’s surface.

Absorbedmostly by CO 2 Short wavelength Long wavelength 0.1 µm (µm = millionth of a metre) 100 µm

Climate science H2O CO2 CH4 Absorption spectra for greenhouse gases

Climate science  That means that even if the atmosphere is saturated with water vapour a lot of IR still gets through.  CO 2 and CH 4 absorb IR wavelengths that H 2 O 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!

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 CO 2 : Global average temperature increase

Climate science  Here is the result with human added CO 2 : Global average temperature increase

Climate science  The models correctly predict volcanic effects 1963 Agung 1982 El Chichon 1991 Pinatubo Global average temperature increase

Climate science  This is why scientists believe that human added CO 2 is a problem! 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:

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.” “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 Temperatures in that interglacial were only a couple of degrees warmer than the 20 th 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

Monthly average temperature increases for December 2009 compared to 1951 – 1980 Average global +0.62°C