Teaching the Physics of Climate Change

Teaching the Teaching the Physics of Physics of

Climate ChangeClimate Change

Keith Burrows

AIP Education Committee

PHYSCON Feb 2008

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- Teaching the Science of Climate Change

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6.2.2 Role of scientists in the climate debate These stark conclusions about the threat

posed by global climate change and implications for fossil fuel use are not yet appreciated by essential governing bodies… In our view, there is an acute need for science to inform society about the costs of failure to address global warming, because of a fundamental difference between the threat posed by climate change and most prior global threats.

J Hansen et alJ Hansen et al

The conclusion from: Dangerous human-made interference with climate: a

GISS modelE study J Hansen et al

In Journal of Atmospheric Chemistry and Physics, 7, 2287–2312, 2007 www.atmos-chem-phys.net/7/2287/2007/

Authors from: NASA Goddard Institute for Space Studies, Columbia

University Earth Institute, Sigma Space Partners LLC, Department of Earth and Environmental Sciences, Columbia University, Department of Applied Physics and Applied Mathematics, Columbia University, Clean Air Task Force, Boston, Goddard Space Flight Center, Laboratoire des Sciences du Climat et de l’Environnement, Department of Geology, Yale University, Lawrence Berkeley National Laboratory, Massachusetts Institute of Technology, Argonne National Laboratory.

http://www.atmos-chem-phys.net/7/2287/2007/

This presentation is This presentation is dedicated to our dedicated to our precious grandchildren precious grandchildren – and all the others who – and all the others who will inherit the results of will inherit the results of our efforts in this our efforts in this decade – the last that decade – the last that has the option to act to has the option to act to avoid dangerous climate avoid dangerous climate change.change.

OverviewOverview Climate scienceClimate science

– Earth’s energy balanceEarth’s energy balance– Interactions between EMR and the atmosphereInteractions between EMR and the atmosphere– The effect of changes in the systemThe effect of changes in the system

Human induced changesHuman induced changes– The release of millions of years of stored energyThe release of millions of years of stored energy– Is the climate changing?Is the climate changing?– How can we understand it? How can we understand it? – Climate models and their predictions.Climate models and their predictions.

What can we do?What can we do?– Fossil fuelsFossil fuels– Reduce energy useReduce energy use– Lower CO2 optionsLower CO2 options– Sustainable optionsSustainable options

The human responseThe human response– Sceptics, deniers, avoidersSceptics, deniers, avoiders– Change the light bulbsChange the light bulbs– The need for real changeThe need for real change

EducationEducation– That’s where we come inThat’s where we come in

ClimateClimate science science Earth’s energy balanceEarth’s energy balance

– The average temperature of the Earth is determined by the balance The average temperature of the Earth is determined by the balance between incoming solar radiation and outgoing ‘heat’ radiationbetween incoming solar radiation and outgoing ‘heat’ radiation

ClimateClimate science science ~ 1/3 reflected~ 1/3 reflected ~ 2/3 absorbed ~ 2/3 absorbed

then re-radiated then re-radiated as IR EMR.as IR EMR.

175,000 TW in175,000 TW in 175,000 TW out175,000 TW out

(That’s if it is in (That’s if it is in equilibrium)equilibrium)


– The average temperature of the Earth is The average temperature of the Earth is determined by the balance between incoming determined by the balance between incoming solar radiation and outgoing ‘heat’ radiationsolar radiation and outgoing ‘heat’ radiation

– Not all the IR radiation from the surface Not all the IR radiation from the surface escapes immediately... escapes immediately...

– or the average temperature would be a freezing or the average temperature would be a freezing –15–15ºC ºC

– and there would be much greater swings and there would be much greater swings between night & day, cloud & no cloudbetween night & day, cloud & no cloud


ClimateClimate science science The Greenhouse effect:The Greenhouse effect:

– Natural:Natural: Water vapourWater vapour Carbon dioxideCarbon dioxide

– Human produced:Human produced: Carbon dioxideCarbon dioxide Methane etc.Methane etc.

Human produced

ClimateClimate science science Interactions between EMR and the atmosphere:Interactions between EMR and the atmosphere:

– Blackbody spectra. All objects at ANY temperature emit EMRBlackbody spectra. All objects at ANY temperature emit EMR– Hot metal emits lots of shorter IR and some visibleHot metal emits lots of shorter IR and some visible

ClimateClimate science science Interactions between EMR and the atmosphere: Interactions between EMR and the atmosphere: Blackbody spectra. All objects at ANY temperature emit EMRBlackbody spectra. All objects at ANY temperature emit EMR

– Cold objects only long IR and no visibleCold objects only long IR and no visible– Slightly shorter IRSlightly shorter IR

ClimateClimate science science Interactions between EMR and the atmosphere: Interactions between EMR and the atmosphere:

– Blackbody spectraBlackbody spectra– Spectra of starsSpectra of stars– or anything else that hotor anything else that hot

– UV Vis IR –

UV IR

The Sun is 5800 K


– Blackbody spectraBlackbody spectra– Sun and EarthSun and Earth

(but note that(but note that

Earth is less thanEarth is less than

a millionth of a millionth of

the Sun)the Sun) Also note that the IR Also note that the IR

absorbed from the absorbed from the Sun is of much Sun is of much shorter wavelength shorter wavelength than that emitted by than that emitted by the Earththe Earth

– UV Vis short IR – long IR


– Types of spectra:Types of spectra:– Blackbody continuous spectrumBlackbody continuous spectrum


– Types of spectra:Types of spectra:– Blackbody continuous spectrum Blackbody continuous spectrum – Emission line spectrumEmission line spectrum


– Types of spectra:Types of spectra:

This is what we are This is what we are interested in.interested in.


– First we need to know something about EMR (light).First we need to know something about EMR (light).– Quantum physics tells us that it comes as ‘photons’Quantum physics tells us that it comes as ‘photons’– Here’s a red oneHere’s a red one– Here’s a violet oneHere’s a violet one– Notice that the violet one has a shorter wavelengthNotice that the violet one has a shorter wavelength– But it has more energyBut it has more energy– (Violet is more violent!)(Violet is more violent!)


– First we need to know something about EMR (light).First we need to know something about EMR (light).– Quantum physics tells us that it comes as ‘photons’Quantum physics tells us that it comes as ‘photons’– Here’s an ultraviolet (UV) one – even shorter wavelengthHere’s an ultraviolet (UV) one – even shorter wavelength– Here’s an infrared (IR) oneHere’s an infrared (IR) one– Notice that the IR one has a longer wavelength againNotice that the IR one has a longer wavelength again– It also has much less energy – It also has much less energy – – but it’s IR that is of interest to usbut it’s IR that is of interest to us


– The gases in the atmosphere absorb, and then re-radiate some The gases in the atmosphere absorb, and then re-radiate some parts of the spectrum but not others.parts of the spectrum but not others.

– The structure of the molecule determines what sort of energy is The structure of the molecule determines what sort of energy is absorbed.absorbed.

– Oxygen and Nitrogen molecules are ‘tight’ and it takes a lot of Oxygen and Nitrogen molecules are ‘tight’ and it takes a lot of energy to ‘shake’ them.energy to ‘shake’ them.

– IR and visible EMR goes right pastIR and visible EMR goes right past– Only high energy UV can give its energy to oxygenOnly high energy UV can give its energy to oxygen– (but there’s very little of that even in sunlight)(but there’s very little of that even in sunlight)


– HH22O and COO and CO22 molecules (and other GHGs) are more ‘floppy’ molecules (and other GHGs) are more ‘floppy’

– and so take on energy more easily and so take on energy more easily – IR gives them energyIR gives them energy– which they re-radiate – in random directions.which they re-radiate – in random directions.– So some goes back down to EarthSo some goes back down to Earth– keeping us warmerkeeping us warmer– The Greenhouse effect!The Greenhouse effect!

C:\Documents and Settings\My Documents\K-CC\PHYS-CON\PHYSCON\carbon-dioxide-greenhouse.mov

ClimateClimate science science The effect of changesThe effect of changes

– Remember we wouldn’t be here without it!Remember we wouldn’t be here without it!– Water vapour is the main GHGWater vapour is the main GHG

– But what if we add more COBut what if we add more CO22??

ClimateClimate science science The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing

– More COMore CO22 → more warmth → more H→ more warmth → more H22O (evaporation) O (evaporation)

→ more warmth → more H→ more warmth → more H22O → more warmth → ???O → more warmth → ???

– Water vapour goes in and out of the atmosphere very Water vapour goes in and out of the atmosphere very quicklyquickly

– Carbon dioxide is there for ~ 100 years Carbon dioxide is there for ~ 100 years – That makes a very big difference in the way they actThat makes a very big difference in the way they act

ClimateClimate science science The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing

– Human Human added Hadded H22O O

is not a is not a problem – it problem – it soon rains soon rains out again.out again.

– But COBut CO22 is is

another another story!story!

ClimateClimate pseudopseudo science science The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing

“the combined effect of these greenhouse gases is to warm Earth's atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity.”

Prof. Bob Carter, Research Professor at James Cook University, palaeontologist, stratigrapher, marine geologist and environmental scientist. [Web link to source of this quote as well as the RealClimate discussion are given on the notes page below]


– His argument in short:– GHE → 33°C (–18ºC to 15ºC)

– H2O → 95% of this (ie.31ºC)

– OGHG → 5% of which CO2 → 3.6%

– Human CO2 is 3% of CO2 so only 0.1% of GHE

– ie. 0.04°C No worries ☺

ClimateClimate RealReal science science The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing

– Sounds impressive – if only! – but Sounds impressive – if only! – but – www.realclimate.orgwww.realclimate.org A group of real climate scientists A group of real climate scientists

who try to help people like Carter – and us.who try to help people like Carter – and us.RealClimate.orgGavin A. Schmidt: climate modeller at the NASA Goddard Institute for Space StudiesDr. Michael E. Mann: Penn State University Departments of Meteorology and Geosciences and the Earth and Environmental Systems Institute, IPCC lead authorDr. Caspar Ammann: National Center for Atmospheric Research (NCAR).Dr. Rasmus E. Benestad: Norwegian project called RegClim, Norwegian Meteorological InstituteProf. Raymond S. Bradley: Director of the Climate System Research Center University of Massachusetts, Ray Bradley: Advisor to U.S., Swiss, Swedish, and U.K. National Science Foundations, NOAA, IPCC, IGBP, Stockholm.William M. Connolley: Climate modeller with the British Antarctic Survey.Prof. Stefan Rahmstorf: New Zealand Oceanographic Institute, Institute of Marine Science in Kiel, Potsdam Institute for Climate Impact Research in Germany, IPCC.Dr. Eric Steig: Isotope geochemist, University of WashingtonDr. Thibault de Garidel: Institute of Marine and Coastal Sciences at Rutgers University.Dr. David Archer: Computational ocean chemist at the University of Chicago.

http://www.realclimate.org/

The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing– H2O 95% should actually be 90-95% and is for

clouds also.– Can’t simply subtract leaving 5-10% for GHGs.– H2O and CO2 absorb different parts of the IR

radiation spectrum.

ClimateClimate RealReal science science

H2O CO2

CH4

The effect of changes – Feedback and ForcingThe effect of changes – Feedback and Forcing– So it doesn’t matter how much water vapour is

in the atmosphere, adding CO2 and CH4 will absorb more IR because they absorb different parts of the IR radiation spectrum.

ClimateClimate RealReal science science

ClimateClimate RealReal science science The effect of changes – Feedback and Forcing The effect of changes – Feedback and Forcing

The Real Science:The Real Science:– Take away all H2O: OGHGs absorb ~34%– Take away OGHGs: H2O absorb ~85%– So effect of H2O ~ 66% – 85% [100 – 34 = 66]

– Not a linear problem!– So Carter’s 5% for OGHGs should be ~ 15% –

34% [100 – 85 = 15]

– So CO2 on its own is 9% – 26% of the GHE [As CO2 is about 60% of GHGs]

– Assuming Carter’s linearity Assuming Carter’s linearity → ΔT ~ 3 to 9°C– (But it isn’t a linear problem)(But it isn’t a linear problem)


– Carter also said that human CO2 is 3% of CO2 so 0.1% of GHE

– ie. 0.04°C No worries ☺– But where did he get that figure from?

?


– Anthropogenic CO2 is NOT 3%!


– Anthropogenic CO2: < 300 ppm → 380 ppm– Rise of > 30% – linear extrapolation: AGHG → 1 to 2.6°C (AGHG = Anthropogenic GHGs)

– so we can all look forward

to more time on the beach!

ClimateClimate science science The effect of changes – The effect of changes – FeedbackFeedback and Forcing and Forcing

– Carter ignores complex mechanisms of the GHE. Assumes effects are linear – Just plain wrong.

– Overlaps: gases absorb overlapping wavelengths.

– Saturation: more gas makes no difference.– Feedback: Particularly important. Positive and

negative.– Positive feedback:

ClimateClimate science science The effect of changes – The effect of changes – FeedbackFeedback and Forcing and Forcing

– Examples of feedback: – Increased water vapour → more clouds– reflect sunlight (negative feedback) – trap IR radiation (positive feedback)

ClimateClimate science science The effect of changes – The effect of changes – FeedbackFeedback and and ForcingForcing

– Water vapour is a ‘Water vapour is a ‘feedbackfeedback’ GHG’ GHG

– COCO22, CH, CH44, O, O33 etc are ‘ etc are ‘forcingforcing’ agents’ agents

– They stay in the atmosphere whatever and ‘force’ They stay in the atmosphere whatever and ‘force’ more heat into the climate system.more heat into the climate system.

– Effect measured by ‘Radiative forcing constant’Effect measured by ‘Radiative forcing constant’

– or: the extra heat flowing into (or out of) the climate system as a result of a change in some part of the system (in W/m²)

"The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values". (IPCC)

ClimateClimate science science The effect of changes – The effect of changes – FeedbackFeedback and and ForcingForcing

– Computer models are the only way of taking all Computer models are the only way of taking all this into account – a little later.this into account – a little later.

OverviewOverview Climate scienceClimate science

– Earth’s energy balanceEarth’s energy balance– Interactions between EMR and the atmosphereInteractions between EMR and the atmosphere– The effect of changes in the systemThe effect of changes in the system

Human induced changesHuman induced changes– The release of millions of years of stored energyThe release of millions of years of stored energy– Is the climate changing?Is the climate changing?– How can we understand it? How can we understand it? – Climate models and their predictions.Climate models and their predictions.

What can we do?What can we do?– Fossil fuelsFossil fuels– Reduce energy useReduce energy use– Lower CO2 optionsLower CO2 options– Sustainable optionsSustainable options

The human responseThe human response– Sceptics, deniers, avoidersSceptics, deniers, avoiders– Change the light bulbsChange the light bulbs– The need for real changeThe need for real change

EducationEducation– That’s where we come inThat’s where we come in

Human induced changesHuman induced changes The release of solar energy and carbon The release of solar energy and carbon

stored over 100 million years ...stored over 100 million years ...

Human induced changesHuman induced changes The release of solar energy and carbon The release of solar energy and carbon

stored over 100 million years in only 100’s of stored over 100 million years in only 100’s of yearsyears

That is, a That is, a MILLION MILLION timestimes faster. faster.

We have to ask We have to ask whether it might have whether it might have an effect!an effect!

Human induced changesHuman induced changes Is the climate changing? Is the climate changing?

IPCC SynRep

Human induced changesHuman induced changes Is the climate changing?Is the climate changing?

Human induced changesHuman induced changes We now know it has:We now know it has:


Human induced changesHuman induced changes Franz Josef glacier NZFranz Josef glacier NZ

Human induced changesHuman induced changes The Arctic Sea Ice is melting at a much faster The Arctic Sea Ice is melting at a much faster

rate than predicted.rate than predicted.

Human induced changesHuman induced changes The Arctic Ice is melting at a much faster rate The Arctic Ice is melting at a much faster rate

than predictedthan predicted

Human induced changesHuman induced changes The Arctic Ice is melting at a much faster rate The Arctic Ice is melting at a much faster rate

than predicted.than predicted. This is a real problem because water absorbs This is a real problem because water absorbs

far more solar energy than snow:far more solar energy than snow: AAverage of Earth 0.3 Albedo of snowAlbedo of snow & ice 0.8 – 0.9 Albedo of waterAlbedo of water 0.07 A positive feedback effectA positive feedback effect


The Greenland summer ice melt is getting larger at a worrying rate.


2001

2002

2003



Human induced changesHuman induced changes The Arctic sea ice is a concern because of The Arctic sea ice is a concern because of

the positive feedback involvedthe positive feedback involved Greenland not only has that, but its melt Greenland not only has that, but its melt

water raises the sea level and makes it less water raises the sea level and makes it less saline.saline.

If all Greenland’s ice were to melt it would If all Greenland’s ice were to melt it would raise the sea level by around 7 metresraise the sea level by around 7 metres

The less saline water may interfere with the The less saline water may interfere with the “global ocean conveyor”.“global ocean conveyor”.

The thermohaline circulation is driven by differences in seawater The thermohaline circulation is driven by differences in seawater density (temperature and salt content). It carries COdensity (temperature and salt content). It carries CO22 to the deep to the deep ocean and distributes heat. It strongly influences climate regimes ocean and distributes heat. It strongly influences climate regimes and the availability of nutrients to marine life. (From UN GEO4)and the availability of nutrients to marine life. (From UN GEO4)

Human induced changesHuman induced changes It has been thought (hoped?) that the Antarctic Ice It has been thought (hoped?) that the Antarctic Ice

sheets are not melting.sheets are not melting.

NASA

Human induced changesHuman induced changes It has been thought (hoped?) that the Antarctic Ice It has been thought (hoped?) that the Antarctic Ice

sheets are not melting.sheets are not melting.

However However (23 Jan 2008):(23 Jan 2008):

Colours indicate Colours indicate speed of ice loss:speed of ice loss:

Red fast, green Red fast, green slowerslower

Loss is on a par Loss is on a par with the Greenland with the Greenland ice loss rate.ice loss rate.

NASA

Human induced changesHuman induced changes Closer to home:Closer to home:“Drought”?

– or changing climate?

Human induced changesHuman induced changes

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Victorian rainfall 2004 – 2007 (3 years)Victorian rainfall 2004 – 2007 (3 years)

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Victorian rainfall 2006 – 2007 Victorian rainfall 2006 – 2007

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia – Very cold daysAustralia – Very cold days

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia – Warm daysAustralia – Warm days

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia – Very hot daysAustralia – Very hot days

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia 2007 – mean temperaturesAustralia 2007 – mean temperatures

Highest on record

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia Temperature trendAustralia Temperature trend

Human induced changesHuman induced changes Is the climate changing?Is the climate changing? Australia Temperature trendAustralia Temperature trend According to Andrew Bolt and Alan Moran:According to Andrew Bolt and Alan Moran:


According to NASA and the climate scientists.


According to NASA and the climate scientists.




2005 worst on record


IPCC SynRep

IPCC SynRep

IPCC SynRep

Human induced changesHuman induced changes How can we understand it?How can we understand it?

– It’s all a matter of physics! It’s all a matter of physics!

This ppt can be downloaded fromThis ppt can be downloaded from

www.vicphysics.orgwww.vicphysics.org – Teachers – Teachers- Feedback:Feedback:- [email protected]@physics.org- Resources:Resources:

realclimate.org

http://www.vicphysics.org/

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