Transcript Climate Change

Teaching the
Physics of
Climate Change
This ppt available on
www.vicphysics.org
Keith Burrows
- Teachers
AIP Education Committee
- Teaching the Science of Climate Change
PHYSCON Feb 2008
 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 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.
 This presentation is
dedicated to our
precious grandchildren
– and all the others who
will inherit the results of
our efforts in this
decade – the last that
has the option to act to
avoid dangerous climate
change.
 Climate science
Overview
– Earth’s energy balance
– Interactions between EMR and the atmosphere
– The effect of changes in the system
 Human induced changes
–
–
–
–
The release of millions of years of stored energy
Is the climate changing?
How can we understand it?
Climate models and their predictions.
 What can we do?
–
–
–
–
Fossil fuels
Reduce energy use
Lower CO2 options
Sustainable options
 The human response
– Sceptics, deniers, avoiders
– Change the light bulbs
– The need for real change
 Education
– That’s where we come in
Climate science
 Earth’s energy balance
– The average temperature of the Earth is determined by the balance
between incoming solar radiation and outgoing ‘heat’ radiation
 ~ 1/3 reflected
 ~ 2/3 absorbed
then re-radiated
as IR EMR.
 175,000 TW in
 175,000 TW out
(That’s if it is in
equilibrium)
Climate science
Climate science
 Earth’s energy balance
– 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
–15ºC
– and there would be much greater swings
between night & day, cloud & no cloud
Climate science
 Earth’s energy balance
Climate science
 The Greenhouse effect:
– Natural:
 Water vapour
 Carbon dioxide
– Human produced:
 Carbon dioxide
 Methane etc.
Human produced
Climate science
 Interactions between EMR and the atmosphere:
– Blackbody spectra. All objects at ANY temperature emit EMR
– Hot metal emits lots of shorter IR and some visible
Climate science
 Interactions between EMR and the atmosphere:
 Blackbody spectra. All objects at ANY temperature emit EMR
– Cold objects only long IR and no visible
– Slightly shorter IR
Climate science
 Interactions between EMR and the atmosphere:
– Blackbody spectra
– Spectra of stars
– or anything else that hot
UV
IR
The Sun
is 5800 K
– UV
Vis IR –
Climate science
 Interactions between EMR and the atmosphere:
– Blackbody spectra
– Sun and Earth
(but note that
Earth is less than
a millionth of
the Sun)
 Also note that the IR
absorbed from the
Sun is of much
shorter wavelength
than that emitted by
the Earth
– UV
Vis short IR –
long IR
Climate science
 Interactions between EMR and the atmosphere:
– Types of spectra:
– Blackbody continuous spectrum
Climate science
 Interactions between EMR and the atmosphere:
– Types of spectra:
– Blackbody continuous spectrum
– Emission line spectrum
Climate science
 Interactions between EMR and the atmosphere:
– Types of spectra:
This is what we are
interested in.
Climate science
 Interactions between EMR and the atmosphere:
–
–
–
–
–
–
–
First we need to know something about EMR (light).
Quantum physics tells us that it comes as ‘photons’
Here’s a red one
Here’s a violet one
Notice that the violet one has a shorter wavelength
But it has more energy
(Violet is more violent!)
Climate science
 Interactions between EMR and the atmosphere:
–
–
–
–
–
–
–
First we need to know something about EMR (light).
Quantum physics tells us that it comes as ‘photons’
Here’s an ultraviolet (UV) one – even shorter wavelength
Here’s an infrared (IR) one
Notice that the IR one has a longer wavelength again
It also has much less energy –
but it’s IR that is of interest to us
Climate science
 Interactions between EMR and the atmosphere:
– The gases in the atmosphere absorb, and then re-radiate some
parts of the spectrum but not others.
– The structure of the molecule determines what sort of energy is
absorbed.
– Oxygen and Nitrogen molecules are ‘tight’ and it takes a lot of
energy to ‘shake’ them.
– IR and visible EMR goes right past
– Only high energy UV can give its energy to oxygen
– (but there’s very little of that even in sunlight)
Climate science
 Interactions between EMR and the atmosphere:
–
–
–
–
–
–
–
H2O and CO2 molecules (and other GHGs) are more ‘floppy’
and so take on energy more easily
IR gives them energy
which they re-radiate – in random directions.
So some goes back down to Earth
keeping us warmer
The Greenhouse effect!
Climate science
 The effect of changes
– Remember we wouldn’t be here without it!
– Water vapour is the main GHG
– But what if we add more CO2?
Climate science
 The effect of changes – Feedback and Forcing
– More CO2 → more warmth → more H2O (evaporation)
→ more warmth → more H2O → more warmth → ???
– Water vapour goes in and out of the atmosphere very
quickly
– Carbon dioxide is there for ~ 100 years
– That makes a very big difference in the way they act
Climate science
 The effect of changes – Feedback and Forcing
– Human
added H2O
is not a
problem – it
soon rains
out again.
– But CO2 is
another
story!
Climate pseudo science
 The 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]
Climate pseudo science
 The effect of changes – Feedback and Forcing
– 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 ☺
Climate Real science
 The effect of changes – Feedback and Forcing
– Sounds impressive – if only! – but 
– www.realclimate.org A group of real climate scientists
who try to help people like Carter – and us.
RealClimate.org
Gavin A. Schmidt: climate modeller at the NASA Goddard Institute for Space Studies
Dr. Michael E. Mann: Penn State University Departments of Meteorology and Geosciences and the
Earth and Environmental Systems Institute, IPCC lead author
Dr. Caspar Ammann: National Center for Atmospheric Research (NCAR).
Dr. Rasmus E. Benestad: Norwegian project called RegClim, Norwegian Meteorological Institute
Prof. 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 Washington
Dr. Thibault de Garidel: Institute of Marine and Coastal Sciences at Rutgers University.
Dr. David Archer: Computational ocean chemist at the University of Chicago.
Climate Real science
 The effect of changes – Feedback and Forcing
– H2O 95% should actually be 90-95% and is for
clouds also.
H2Oleaving 5-10% for
– Can’t simply subtract
GHGs.
CO2
– H2O and CO2 absorb different parts of the IR
radiation spectrum.CH4
Climate Real science
 The 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.
Climate Real science
 The effect of changes – Feedback and Forcing
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 → ΔT ~ 3 to 9°C
– (But it isn’t a linear problem)
Climate pseudo science
 The effect of changes – Feedback and Forcing
– 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?
?
Climate Real science
 The effect of changes – Feedback and Forcing
– Anthropogenic CO2 is NOT 3%!
Climate Real science
 The effect of changes – Feedback and Forcing
– 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!
Climate science
 The effect of changes – Feedback 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:
Climate science
 The effect of changes – Feedback and Forcing
– Examples of feedback:
– Increased water vapour → more clouds
– reflect sunlight (negative feedback)
– trap IR radiation (positive feedback)
Climate science
 The effect of changes – Feedback and Forcing
– Water vapour is a ‘feedback’ GHG
– CO2, CH4, O3 etc are ‘forcing’ agents
– They stay in the atmosphere whatever and ‘force’
more heat into the climate system.
– Effect measured by ‘Radiative forcing constant’
"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)
– 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)
Climate science
 The effect of changes – Feedback and Forcing
– Computer models are the only way of taking all
this into account – a little later.
 Climate science
Overview
– Earth’s energy balance
– Interactions between EMR and the atmosphere
– The effect of changes in the system
 Human induced changes
–
–
–
–
The release of millions of years of stored energy
Is the climate changing?
How can we understand it?
Climate models and their predictions.
 What can we do?
–
–
–
–
Fossil fuels
Reduce energy use
Lower CO2 options
Sustainable options
 The human response
– Sceptics, deniers, avoiders
– Change the light bulbs
– The need for real change
 Education
– That’s where we come in
Human induced changes
 The release of solar energy and carbon
stored over 100 million years ...
Human induced changes
 The release of solar energy and carbon
stored over 100 million years in only 100’s of
years
That is, a MILLION
times faster.
We have to ask
whether it might have
an effect!
Human induced changes
 Is the climate changing?
IPCC SynRep
Human induced changes
 Is the climate changing?
Human induced changes
 We now know it has:
Human induced changes
 We now know it has:
Human induced changes
 Franz Josef glacier NZ
Human induced changes
 The Arctic Sea Ice is melting at a much faster
rate than predicted.
Human induced changes
 The Arctic Ice is melting at a much faster rate
than predicted
Human induced changes
 The Arctic Ice is melting at a much faster rate
than predicted.
 This is a real problem because water absorbs
far more solar energy than snow:
 Average of Earth 0.3
 Albedo of snow & ice 0.8 – 0.9
 Albedo of water 0.07
 A positive feedback effect
Human induced changes
 Is the climate changing?
The
Greenland
summer ice
melt is
getting larger
at a worrying
rate.
2001
2002
2003
The
Greenland
summer ice
melt is
getting larger
at a worrying
rate.
Human induced changes
 Is the climate changing?
The
Greenland
summer ice
melt is
getting larger
at a worrying
rate.
Human induced changes
 The Arctic sea ice is a concern because of
the positive feedback involved
 Greenland not only has that, but its melt
water raises the sea level and makes it less
saline.
 If all Greenland’s ice were to melt it would
raise the sea level by around 7 metres
 The less saline water may interfere with the
“global ocean conveyor”.
The thermohaline circulation is driven by differences in seawater
density (temperature and salt content). It carries CO2 to the deep
ocean and distributes heat. It strongly influences climate regimes
and the availability of nutrients to marine life. (From UN GEO4)
Human induced changes
 It has been thought (hoped?) that the Antarctic Ice
sheets are not melting.
NASA
Human induced changes
 It has been thought (hoped?) that the Antarctic Ice
sheets are not melting.
 However
(23 Jan 2008):
 Colours indicate
speed of ice loss:
Red fast, green
slower
 Loss is on a par
with the Greenland
ice loss rate.
NASA
Human induced changes
“Drought”?
 Closer
to home:
– or changing climate?
Human induced changes
Human induced changes
 Is the climate changing?
 Victorian rainfall 2004 – 2007 (3 years)
Human induced changes
 Is the climate changing?
 Victorian rainfall 2006 – 2007
Human induced changes
 Is the climate changing?
 Australia – Very cold days
Human induced changes
 Is the climate changing?
 Australia – Warm days
Human induced changes
 Is the climate changing?
 Australia – Very hot days
Human induced changes
 Is the climate changing?
 Australia 2007 – mean temperatures
Highest on record
Human induced changes
 Is the climate changing?
 Australia Temperature trend
Human induced changes
 Is the climate changing?
 Australia Temperature trend
 According to Andrew Bolt and Alan Moran:
Human induced changes
According
to NASA
and the
climate
scientists.
Human induced changes
According
to NASA
and the
climate
scientists.
Human induced changes
 We now know it has:
Human induced changes
 Is the climate changing?
Human induced changes
 Is the climate changing?
2005 worst on record
Human induced changes
 Is the climate changing?
IPCC SynRep
IPCC SynRep
IPCC SynRep
Human induced changes
 How can we understand it?
– It’s all a matter of physics!
 This ppt can be downloaded from
www.vicphysics.org – Teachers
- Feedback:
- [email protected]
- Resources:
realclimate.org