Transcript Climate Change - Day 3

IPCC
1992: Still trying to sort out effects of natural variation and
human impacts
1996: “The balance of evidence suggests a discernible
human influence on global climate”
2001: Humans are “likely” to cause global warming
2007: Humans are “very likely” to cause global warming.
Two notes: 1) In scientific talk, it does not get much more
certain than “very likely”; and 2) The IPCC is inherently
conservative and often supports minimum possible
climate change (rather than maximum possible change).
Projections of human behaviour not easily amenable to
prediction (e.g. evolution of political systems).
Chaotic components of complex systems.
Inadequate models, incomplete or competing conceptual
frameworks, lack of agreement on model structure,
ambiguous system boundaries or definitions, significant
processes or relationships wrongly specified or not
considered.
Missing, inaccurate or non-representative data,
inappropriate spatial or temporal resolution,
poorly known or changing model parameters.
Images from IPCC report
Radiative Forcing
To compare different variables, you need a
common unit (to compare apples with apples, as
the saying goes).
Radiative forcing is the difference between the
incoming radiation energy and the outgoing
radiation energy in a given climate system.
A positive forcing (more incoming energy)
tends to warm the system, while a negative
forcing (more outgoing energy) tends to cool it.
3
A Watt (as in James)
A unit of power = Work / time
(Your standard household bulb uses 60 Watts)
Because we care about the Earth’s surface,
we use Watts/meters2
I like steam engines. A lot.
4
Image from Thinkquest
So, what causes radiative
forcing?
Solar input - relatively constant, but can be
slightly higher or lower than usual
Chinese records of sunspots go back to Book of Changes
(800 B.C.E.): "A dou is seen in the Sun" and "A mei is seen
in the Sun". ”Dou" and "mei" are taken to mean darkening
or obscuration.
Image from nasa.gov
Sunspots
Author: Hans Bernhard
So, what causes radiative
forcing?
Solar input - relatively constant, but can be
slightly higher or lower than usual
CO2 (& other greenhouse gases) - increases
radiative forcing
Aerosols - decreases radiative forcing
2.5
CO2
2.0
W/m2
1.5
1.0
Solar
0.5
0.0
Temperature
-0.5
-1.0
1800
Aerosols
1850
1900
Year AD
1950
2000
Components of a fully coupled general circulation model
Removed image due to
copywright. It can be found at
the Australian Department of
Meteorology.
GCMs contain our best current understanding for how the physical processes
interact (for instance, how evaporation depends on the wind and surface
temperature, or how clouds depend on the humidity and vertical motion) while
conserving basic quantities like energy, mass and momentum. These estimates
are based on physical theories and empirical observations made around the world.
Development of climate models over time
IPCC, adopted by Australian Department of Climate Change and
Energy Efficiancy
Models
We cannot predict how one variable will inherently
influence another. Therefore, we have to make
models. Models lead to “emergent” properties,
which is large scale behavior that is not a priori
predictable from the small scale interactions that
make up the system.
Models are inherently theoretical. As such, they
are often very quantitative.
Models (con’t)
All models are wrong; some models are useful.
-G.E. Box (UW Professor)
These models are all simplifications of the actual phenomena. But
these models can still be valuable.
The problem with models (or any theoretical approach) lie in the assumptions.
IPCC: Critical aspects
Validation - assessment of the accuracy of
the model
Attribution - the ability to assign causes to
effects (distinguish causation from
correlation)
Prediction - specification, in advance, of
events or changes in a system
Validation
Validation reflects an assessment of the
accuracy (not precision) of the model.
This is done by attempting to duplicate
current climate data, or “backcasting” (as
opposed to forecasting) past climates when
the Earth was very different (such as 18,000
years ago, during the maximum extent of the
ice age).
Image from IPCC
Science is the investigation of
the natural world, based on
the rules of reason and logic.
Science is testable and/or
predictable.
How do you test a model,
particularly of a GCM (Global
Climate Model)?
1981
Image from USGS
Image source: New York Times
We can test our GCM!
1963 Mount Agung (Indonesia)
volcanic eruption
(ok, really, this is a picture of the
1991 Mount Pinatubo eruption)
Jim Hansen
They found that the changes calculated by their simple model
corresponded in all essential respects — including timing and
approximate magnitude — to the observed global temperature
changes. The GCM worked!
But, more importantly, the the results also showed that volcanic
aerosols could significantly cool the surface.
Hot dog! It works!
Image source: New York Times
Attribution
The ability to assign causes to
effects.
This is a problem inherent in
systems with multiple variables.
The simplest approach is
“sensitivity analysis”, in which
each variable is tested for its
possible effect. The IPCC report
is all about attribution.
Is CO2 the only greenhouse gas
that is important?
It turns out (unfortunately), no.
1) Methane (CH4) - From rice paddies and cows.
2) N2O - from agriculture, including fertilizer
3) Ozone (O3) - not anthropogenic
and…
4) CFCs (Chloroflorocarbons) - From refrigeration
and spray (and fire retardant)
The big problem is that these gases could be much more potent than CO2.
But, an even bigger problem was,……
Image from NOAA
Image from NASA
Despite the fact that these gases are much less abundant, they are much
more potent than CO2. But, for the case of CFCs, there was an even bigger
problem…..
The Ozone hole
In addition to being
greenhouse gases, CFCs
destroy ozone (O3).
Consequently, they cause
an ozone hole over the
South Pole.
Note that the ozone hole
has no effect on global
warming (except that the
presence of CFCs both
destroys the ozone AND
causes global warming).
Source: NASA
The Ozone hole
CFC’s in the
stratosphere =
Ozone hole.
CFC’s in the
troposphere =
global warming
Source: NASA
The Ozone hole
This ozone debate plays out like this:
1. Scientists report that CFCs are causing problems
with ozone layer.
2. Industry denies that this is a problem.
3. Scientists confirm this problem.
4. Industry maintains that it is too expensive to
switch to other propellants in spray bottles.
5. Under international pressure, CFCs are
outlawed* in the 1997 Montreal accords.
6. Industry finds new propellants (there is no major
loss in the spray industry and some indications
that there is some economic gain by switching
away from CFCs).
*CFCs are still being produced in some third world countries.
Source: NASA
IPCC
Prediction
Specification, in advance, of events or
changes in a system.
Again, the IPCC includes many predictions,
based on the outcomes of the GCMs.
IPCC & GCMs
The IPCC reports are
based on the composite
results of a variety of
different GCMs.
It is important to realize
that the GCMs just act to
quantifiy (“put numbers
on”) the effects that are
already occurring.
Source: Wikipedia
National Center for Atmospheric
Research laboratory in Boulder,
Colorado
IPCC 2007
Image from NASA
Image from NASA
Image by Robert A. Rohde for Global Warming Art
GCMs are a different approach to
science:
Although we can separate the variables
and treat each individually, they
interact with each other.
This type of interaction requires that
you do science in a different way
than has been done in the past:
Integrated and with a systems
approach. This is sometimes
known as holistic. This approach
must be done IN ADDITION to the
reductionist approach.
This is the second of the major
divisions in science:
1) Empirical-theoretical
2) Reductionistic-holistic
Source: Robert A. Rohde
Holistic science
An analogy
(Image of
doctor and
patient)
The doctor can help a patient who has cancer. But, this
solves a symptom, not the cause. Society is usually
willing to solve a symptom.
But, if you want to really solve the problem, you have to
study the system. This requires a systematic
approach, looking at environmental, genetic
predisposition, and individual facts (the field of
epidemiology) as well as basic understanding of cell
processes (molecular biology).
(Image of
scientists studying
a town)
The medical community has been extremely successful at getting both
funded. This is less true for the scientific community.
Holistic science & Science of
the future
Problem based
Interdisciplinary
Problems of society, not problems of
science (such as, How do we maintain a
habitable Earth?)
Emphasis on predictive power of science
Systems with multiple
variables
1) Sensitivities
2) Positive feedbacks
3) Negative feedbacks
4) Thresholds (“Tipping points”)
5) Complexity (non-linear
feedbacks)
Thresholds
Source: Wikimedia Commons, Bart de Goeij
Side view
Source: Wikimedia Commons, Gertjan R.
Back view
Feedback Loops & Tipping
Points
http://www.youtube.com/watch?v=5T_3WJP
YY9g
First 6:45 of video
Tipping points
http://www.youtube.com/watch?v=XJNH3HT
Dpuk
Interview with Jim Hansen
After 1975, it is all about Global
Climate Models
• 1956 – first GCM (Phillips)
• 1975 – model of 2xCO2 predicts several
degree warming (Manabe)
• 1981 – models show sulfate aerosols =
cooling (Hansen)
• 1991-1995 – model predicts cooling via
Pinnatubo. Verified in 1995. (Hansen)
• 1998 – models can recreate ice-age
climates