Transcript (condensed)(large file! 10Mb) - Department of Physics and Astronomy

Selected Slides from Prof. Broccoli’s
Two Guest Lectures
• Required reading for Greenhouse Effect
class at Rutgers University, Spring
2004
• Condensed by Sunil Somalwar
Global Warming
Alan Robock
Tony Broccoli
Department of Environmental Sciences
Rutgers University, New Brunswick, New Jersey USA
[email protected]
[email protected]
http://envsci.rutgers.edu/~robock
http://envsci.rutgers.edu/~broccoli
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Mann et al.
(1999)
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
“The unequivocal detection of the enhanced greenhouse effect
from observations is not likely for a decade or more.”
Climate Change – The IPCC Scientific Assessment (1990)
“The balance of evidence suggests
a discernible human influence on global climate.”
Climate Change 1995 – The Second Assessment of the
Intergovernmental Panel on Climate Change (IPCC)
“There is new and stronger evidence that
most of the warming observed over the last 50
years is attributable to human activities.”
Climate Change 2000 – The Third Assessment Report
of the IPCC
Alan Robock & Tony Broccoli
Department of Environmental Sciences
At the request of U.S. President George W. Bush, the
National Research Council of the U.S. National Academy
of Sciences issued a special report, Climate Change
Science: An Analysis of Some Key Questions, that
endorsed the key conclusions of the IPCC assessment in
2001.
The U.S. Environmental Protection Agency in 2002 issued
a report that again supported the IPCC assessement.
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Actual 1994-98 observations
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Climate System
1. Atmosphere
2. Hydrosphere (oceans)
3. Cryosphere (snow, ice, glaciers)
4. Biosphere (including people)
5. Lithosphere (soil, volcanoes)
Alan Robock & Tony Broccoli
Department of Environmental Sciences
The Climate System
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Temperature Feedbacks
–
+
+
+
–
–
External forcing
Alan Robock & Tony Broccoli
Department of Environmental Sciences
–
–+
Start with
temperature
increase, e.g.,
from more CO2
Fundamental Determinants of Climate
1. Input of solar radiation
2. Atmospheric composition (gases and aerosols)
3. Surface characteristics (albedo, roughness,
potential evapotranspiration)
Humans can change climate by affecting 2 or 3.
Alan Robock & Tony Broccoli
Department of Environmental Sciences
The climate system
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Planetary albedo (a) is the
average reflectivity of the
Earth = 107/342  0.3
Earth’s global, annual mean energy balance
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Greenhouse effect
Earth’s global, annual mean energy balance
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Causes of Climate Change (Forcings)
Natural:
Anthropogenic:
Solar variations
Volcanic eruptions
Chaotic weather variations
El Niño/Southern Oscillation
Other ocean-atmosphere interactions
GHG: CO2, CH4, CFCs, N2O, O3
Tropospheric aerosols
Sulfates, black carbon, organics, dust
Direct and indirect effects
Ozone depletion (indirect effect of CFCs)
Land surface modification
Contrails
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
(IPCC TAR, Chap. 3)
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Mountain Glacier Trends
Alan Robock & Tony Broccoli
Department of Environmental Sciences
2002
1991
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
General Circulation Models (GCMs) 1
Basic Physical Laws:
Conservation of energy (First law of thermodynamics)
Conservation of momentum (Newton’s second law of motion)
Conservation of mass (Continuity equation)
Conservation of moisture
Hydrostatic equilibrium
Gas law
Alan Robock & Tony Broccoli
Department of Environmental Sciences
General Circulation Models (GCMs) 2
Physical Processes That Must or Can Be Included:
Wind
Sea ice
Radiation
Snow
Precipitation
Glaciers
Soil moisture
Vegetation
Ground water
Ocean biota
Aerosols
Clouds, convective and large-scale
Air-sea exchanges of moisture, energy, and momentum
Air-land exchanges of moisture, energy, and momentum
Chemistry, particularly O3 and CO2
Ocean temperature, salinity, and currents
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Typical grid spacing of a GCM is 4° x 5° latitude-longitude
by 2 km in the vertical.
In the near future, we will have global 1° x 1° models and
the Japanese have designed the fastest computer in the
world, the “Earth Simulator.” on which they will run a global
10 km x 10 km grid.
Each time the horizontal resolution is increased by a factor
of 2, the time needed to run the model goes up by a factor
of 8.
When the vertical resolution is doubled the time required
doubles in general, but can go up by more, if winds become
faster.
Alan Robock & Tony Broccoli
Department of Environmental Sciences
To include all the processes in a climate model which are of
a scale smaller than is resolved by the model, they must be
“parameterized.”
One of the most important and difficult climate elements
to parameterize is cloudiness. Clouds have a much smaller
spatial and temporal scale than a typical GCM grid box.
Usually, we consider separately 2 types of clouds, layer
clouds and convective clouds. There is no fundamental
prognostic equation for clouds (no conservation of clouds
principle); rather they form when condensation takes place
and dissipate due to precipitation and evaporation.
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Future Sea Level Projections
Different scenarios
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Model ranges
Third Assessment Report of the IPCC (2001):
General circulation model results
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Third Assessment Report of the IPCC (2001):
General circulation model results
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Third Assessment Report of the IPCC (2001):
General circulation model results
Pinatubo
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Vinnikov et al.
(1999)
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
How will climate
change affect us?
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Climate Change and other Environmental Stresses
Land Use
Change
Loss of
Biodiversity
Invasive
Species
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Air
Pollution
Acid
Deposition
Areas of Human Endeavor That Could Be
Affected by Global Warming
Agriculture
Water Resources
Fisheries
Air Pollution
Human Health
Recreation
Insurance
Wetlands
Forestry
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Electricity Demand
Wind Energy Generation
Solar Energy Generation
Hydroelectricity Generation
Ocean Transportation
Air Transportation
Land Transportation
Political Systems
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Alan Robock & Tony Broccoli
Department of Environmental Sciences
The Global Warming Dilemma (Mahlman, 2002)
“On the one hand, large increases in atmospheric CO2
concentrations have occurred, with considerably more ‘in the
pipeline.’ Yet, the magnitude of documented warming to date
is comparatively small, about 0.6°C....Thus, there has been
little motivation today to resort to a major effort to reduce
global CO2 emissions.
“On the other hand, delaying major CO2 emissions
reductions until substantial climate warming occurs would
very likely ‘wire in’ the world to globally troublesome global
warming for many centuries....Therefore, the choices are
quite daunting: we can make very large policy commitments
now with little visible short-term payback, or we can delay
policy action indefinitely (the de facto current strategy),
with very large coping and adaptation costs decades and
centuries from now.”
Alan Robock & Tony Broccoli
Department of Environmental Sciences
The Global Warming Dilemma (Mahlman, 2002)
“The harsh reality of the Global Warming Dilemma:
Consider the policymakers’ sincere question: “What can we
do in a mitigation context to keep global warming from
happening?” The blunt answer is almost nothing; climate
change is well underway and it carries huge momentum.
Clearly, the question needs to be restated: “What are the
options available for us to manage this dauntingly difficult
problem in the most globally responsible way?” In this
form, the question is quite reasonable because it allows
avenues for finding rational approaches for dealing with
the real problem.”
Alan Robock & Tony Broccoli
Department of Environmental Sciences
The Global Warming Dilemma (Mahlman, 2002)
“There are no quick policy fixes, nationally or
globally. If we don't begin to chip away at the problem
soon, it is very likely that serious consequences will be
wired in for the world of our great-grandchildren and for
their great-grandchildren. ...
The long time scales and robustness of the problem
almost guarantees that our descendants in the 22nd
century will, with historical perspective, see that we were
actually confronted with a major planet-scale stewardship/
management problem.
They will most assuredly note how we responded,
or how we did not respond to the problem.”
Alan Robock & Tony Broccoli
Department of Environmental Sciences
Frequently Asked Questions
• What is the global warming controversy?
• Was the mild weather of some recent winters
a result of global warming?
• Does global warming mean that there won’t
be snowy winters anymore?
• If global warming is occurring, why was
January so cold?
• How can we project what the earth’s
temperature will be 50 years from now if we
don’t always get tomorrow’s weather forecast
right?
What is the global warming
controversy?
Media Coverage
of Global
Warming
Climate change is a big and
very complex scientific and
political issue. Media coverage
naturally reports on both of
these aspects – often blending
the two.
Time Magazine
April 9, 2001
“Climbing temperatures. Melting glaciers.
Rising Seas. All over the earth we’re
feeling the heat. Why isn’t Washington?”
The Global Warming
Controversy
• Is the earth warming? (Detection)
• Are human activities responsible for
this warming? (Attribution)
• What should we do about it? (Policy)
Was the mild weather of some
recent winters a result of
global warming?
A Baseball Analogy
• John Doe is a five-year veteran with
career averages of .303 BA, 9 HR, 57 RBI.
• He undertakes an off-season weighttraining program.
• In his first at-bat of the new season, he
hits a towering, 470-foot home run.
• Was this monstrous blast a result of his
off-season weight training?
Possible Answers
• “Of course not. One home run doesn’t
prove anything. The pitcher may have
thrown a batting practice fastball that
anybody could crush.”
• “I knew all his off-season work would pay
off. He’s always been able to get his bat
on the ball, he just needed some more
strength. I bet he wins the home run title.”
A Better Answer
• Global warming would alter the probability
of warm winters, but the internal variability
of the climate system is a powerful factor
in year-to-year climate variations.
• A warm winter could be evidence of global
warming, but only if it is part of a long-term
trend.
• Time will tell.
No Snowy Winters Anymore?
• Global warming would alter the
probability of snowy winters, but the
internal variability of the climate system
(e.g., El Niño, North Atlantic Oscillation)
is a powerful factor in year-to-year
climate variations.
If global warming is occurring,
why was January so cold?
Global Temperature Trends
Source: NASA Goddard Institute for Space Studies
How can we project what the
earth’s temperature will be 50
years from now if tomorrow’s
weather forecast isn’t always
right?
2
Xn+1 = a Xn - Xn
X0
a
Precision
(decimal places)
2.200
3.930
2.200
3.940
2.210
3.930
2.20
3.93
7
8
9
10
11
12
13
14
15
16
17
18
19
20
3.807
0.468
1.620
3.742
0.703
2.269
3.769
0.607
2.017
3.859
0.274
1.002
2.934
2.922
2.924
2.971
2.879
3.055
2.704
3.342
1.999
3.880
0.233
0.864
2.658
3.408
1.813
3.856
3.853
0.297
1.079
3.076
2.627
3.423
1.735
3.808
0.465
1.611
3.736
0.725
2.324
3.732
3.68
0.92
2.77
3.21
2.31
3.74
0.71
2.29
3.76
0.64
2.11
3.84
0.35
1.25
Consider a prediction using the above equation of
3
3
3
2
the future state of the variable X, say the surface
air temperature.
The
subscript
n indicates
the
Initial
n (Time Step)
Control
Physics
Rounding
Conditions
time, say the 0 day, 2.200
and a 2.200
is a constant
representing
2.210
2.20
3.806
3.828
3.801
3.81
the physics of12 the climate
system.
X
for any day
0.472
0.429
0.490
0.46
1.506
1.686
1.60
is a times its 34value 1.632
on
the
previous
day
minus X
3.750
3.666
3.783
3.73
5 previous
0.675
1.004
0.556
0.75
squared on the
day.
6
2.197
2.948
1.876
2.39
With such a simple equation, it should be possible to
predict X indefinitely into the future. Right?
2
Xn+1 = a Xn - Xn
X0
a
Precision
(decimal places)
2.200
3.930
2.200
3.940
2.210
3.930
2.20
3.93
3
3
3
2
n (Time Step)
Control
Physics
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
2.200
3.806
0.472
1.632
3.750
0.675
2.197
3.807
0.468
1.620
3.742
0.703
2.269
3.769
0.607
2.017
3.859
0.274
1.002
2.934
2.922
2.200
3.828
0.429
1.506
3.666
1.004
2.948
2.924
2.971
2.879
3.055
2.704
3.342
1.999
3.880
0.233
0.864
2.658
3.408
1.813
3.856
Initial
Conditions
2.210
3.801
0.490
1.686
3.783
0.556
1.876
3.853
0.297
1.079
3.076
2.627
3.423
1.735
3.808
0.465
1.611
3.736
0.725
2.324
3.732
Rounding
2.20
3.81
0.46
1.60
3.73
0.75
2.39
3.68
0.92
2.77
3.21
2.31
3.74
0.71
2.29
3.76
0.64
2.11
3.84
0.35
1.25
Let’s assume that a is exactly 3.930 and that a
prediction with three decimal places is the exact
solution.
Then let’s consider three types of errors:
imprecise knowledge of the physics of the climate
system, imprecise initial conditions, and rounding
due to limited computer resources.
This example is from Edward Lorenz.
2
Xn+1 = a Xn - Xn
X0
a
Precision
(decimal places)
2.200
3.930
2.200
3.940
2.210
3.930
2.20
3.93
3
3
3
2
n (Time Step)
Control
4.0
3.5
3.0
2.5
Xn 2.0
1.5
1.0
0.5
0.0
0
1
2
Control
3
0
1
2
3
4
5
6
7
8
9
10
11
12
13
4
14
15
16
17
18
19
20
Xn+1 =Physics
a Xn Conditions
- Xn2
2.200
3.806
0.472
1.632
3.750
0.675
2.197
3.807
0.468
1.620
3.742
0.703
2.269
5
63.7697
0.607
2.017
3.859
0.274
Physics
1.002
2.934
2.922
Initial
Rounding
2.200
2.210
3.828
3.801
0.429
0.490
1.506
1.686
3.666
3.783
1.004
0.556
2.948
1.876
2.924
3.853
2.971
0.297
2.879
1.079
3.055
3.076
2.704
2.627
3.342
3.423
1.999
1.73512 13
8
9 10 11
3.880
3.808
0.233 n
0.465
0.864
1.611
2.658
3.736
Initial
Conditions
3.408
0.725
1.813
2.324
3.856
3.732
2.20
3.81
0.46
1.60
3.73
0.75
2.39
3.68
0.92
2.77
3.21
2.31
3.74
0.71
14
2.29
3.76
0.64
2.11
3.84
0.35
1.25
15
16
17
18
Rounding
19
20
Sensitivity to Initial Conditions
Results from
three different
simulations,
each starting
from different
initial
conditions.
Changes in
atmospheric
composition
are identical.
Global Warming Occurs in All
Three
The global
warming signal
eventually
emerges in all
three
simulations,
despite the
pronounced
internal
variability that
is evident.
My Global Warming Forecast
• The global climate will continue to warm, and
as it does, any scientific controversy about
the detection of climate change will end.
• Controversy about the attribution of climate
change will last longer than controversy about
the detection of climate change.
• The controversy will eventually shift toward
the policy questions and remain for a long
time.
However…
• Virtually all forecasts should be expressed
as probability forecasts, and mine is no
exception.
• We still have a lot to learn about how the
climate system works.
• More work will be required to narrow the
range of uncertainties about the future
spatial and temporal evolution of climate.