Transcript Computer Modeling of the Global Climate & its Role in the Assessment of Climate Change Keith W.

Computer Modeling of the
Global Climate & its Role in the
Assessment of Climate Change
Keith W. Dixon
research meteorologist
NOAA / Geophysical Fluid Dynamics Laboratory
Princeton, NJ
NROW IX
Albany, New York
7 Nov 2007
My Background
• Undergrad & Grad work @ Rutgers Univ. Met. Dept.
• Radio Wx with Norm MacDonald in early 80’s –
13 stations in NE US (anyone here remember him?).
• Meteorological consulting work in early 80’s.
• Research meteorologist at NOAA Geophysical Fluid
Dynamics Lab (GFDL) for 20+ years.
• Taught undergrad course at Rutgers in late 80’s and
early 90s.
• Favorite Wx Event: The Megalopolitan Snowstorm of
Feb 1983… thunder snow & getting to close Rutgers!
My Background
• Undergrad & Grad work @ Rutgers Univ. Met. Dept.
• Radio Wx with Norm MacDonald in early 80’s –
13 stations in NE US (anyone here remember him?).
• Meteorological consulting work in early 80’s.
• Research meteorologist at NOAA Geophysical Fluid
Dynamics Lab (GFDL) for 20+ years.
• Taught undergrad course at Rutgers in late 80’s and
early 90s.
• Favorite Wx Event: The Megalopolitan Snowstorm of
Feb 1983… thunder snow & getting to close Rutgers!
My Background
• Undergrad & Grad work @ Rutgers Univ. Met. Dept.
• Radio Wx with Norm MacDonald in early 80’s –
13 stations in NE US (anyone here remember him?).
• Meteorological consulting work in early 80’s.
• Research meteorologist at NOAA Geophysical Fluid
Dynamics Lab (GFDL) for 20+ years.
• Taught undergrad course at Rutgers in late 80’s and
early 90s.
• Favorite Wx Event: The Megalopolitan Snowstorm of
Feb 1983… thunder snow & getting to close Rutgers!
Outline:
• Part 1) Public Talk – early 2007 vintage
A “Science Briefing” on Physical Climate
Science… decadal to centennial time scale
climate variability and change & the role of
climate modeling.
• Part 2) Update: Some FAQs, including how
physical climate science fits into the
expanding scope of “the climate change
challenge”. Building upon previous Q&A.
Communications challenges.
Outline:
common thread = separating “signal” from “noise”
• The distinction between Climate Change Science
& Climate Change Policy
(science that is “policy relevant” not “policy prescriptive”)
• Looking Back (1860-present): past climate variability
& change – an issue of Detection & Attribution
(a synthesis of observations, theory & models)
• Looking Ahead: Future scenarios and model
projections for the 21st century and beyond
(climate change commitment… factors in the equation …
a matter of scale)
•
Summary and Q&A
• For related info go to:
http://www.gfdl.noaa.gov/research/climate/highlights
http://www.ipcc.ch (Working Group 1 = WG1)
http://www.ametsoc.org/policy/2007climatechange.html
http://www.climatescience.gov (US Climate Change
Science Program)
Outline:
common thread = separating “signal” from “noise”
• The distinction between Climate Change Science
& Climate Change Policy
(science that is “policy relevant” not “policy prescriptive”)
• Looking Back (1860-present): past climate variability
& change – an issue of Detection & Attribution
(a synthesis of observations, theory & models)
• Looking Ahead: Future scenarios and model
projections for the 21st century and beyond
(climate change commitment… factors in the equation …
a matter of scale)
•
Summary and Q&A
• For related info go to:
http://www.gfdl.noaa.gov/research/climate/highlights
http://www.ipcc.ch (Working Group 1 = WG1)
http://www.ametsoc.org/policy/2007climatechange.html
http://www.climatescience.gov (US Climate Change
Science Program)
Outline:
common thread = separating “signal” from “noise”
• The distinction between Climate Change Science
& Climate Change Policy
(science that is “policy relevant” not “policy prescriptive”)
• Looking Back (1860-present): past climate variability
& change – an issue of Detection & Attribution
(a synthesis of observations, theory & models)
• Looking Ahead: Future scenarios and model
projections for the 21st century and beyond
(climate change commitment… factors in the equation …
a matter of scale)
•
Summary and Q&A
• For related info go to:
http://www.gfdl.noaa.gov/research/climate/highlights
http://www.ipcc.ch (Working Group 1 = WG1)
http://www.ametsoc.org/policy/2007climatechange.html
http://www.climatescience.gov (US Climate Change
Science Program)
Media Coverage of
Climate Change Issue
Climate change is a big and
complex scientific and
political/social issue. The media
reports on both aspects – often
blending the two.
Though a political consensus
may not exist in the US, the
strong scientific consensus is
that we are seeing more signs
that human induced climate
change is real and that change
will become more rapid.
Time Magazine
April 9, 2001
“Climbing temperatures. Melting glaciers.
Rising seas. All over the earth we’re
feeling the heat. Why isn’t Washington?”
Media Coverage of
Climate Change Issue
Climate change is a big and
complex scientific and
political/social issue. The media
reports on both aspects – often
blending the two.
Though a political consensus
may not exist in the US, the
strong scientific consensus is
that we are seeing more signs
that human-caused climate
change is real and that change
will become more rapid.
Time Magazine
April 9, 2001
“Climbing temperatures. Melting glaciers.
Rising seas. All over the earth we’re
feeling the heat. Why isn’t Washington?”
Not a SCIENTIFIC QUESTION, so I’m not going there in this talk!
Media Coverage of
Climate Change Issue
Climate change is a big and
complex scientific and
political/social issue. The media
reports on both aspects – often
blending the two.
Though a political consensus
may not exist in the US, the
strong scientific consensus is
that we are seeing more signs
that human-caused climate
change is real and that change
will become more rapid.
Time Magazine
April 9, 2001
“Climbing temperatures. Melting glaciers.
Rising seas. All over the earth we’re
feeling the heat. Why isn’t Washington?”
Fermenting Froth vs. Scientific Consensus
Sources of Scientific Info:
Individual peer-reviewed scientific
papers… (typically journal articles are
officially reviewed by 2 or 3 people,
as opposed to dozens or hundreds who
are involved in the preparation of large
“assessment” reports like IPCC, CCSP, etc.)
The ideas contained in the
individual papers are bits of the
“fabulous fermenting froth*” of
scientific investigation.
The assessment reports serve to
distill the information and
communicate the policy relevant
bits that stand up.
(*paraphrase of Richard Alley during Congressional
Hearing of 8 Feb 2007)
Climate Change: A Matter of Contending Perspectives
(after Mike MacCracken)
Different
cost/benefit
analyses are
done by those
with these
different
perspectives,
but all are
linked to the
underlying
climate science.
The
National Media
Economics
Security
Ethics
Politics
CLIMATE
SCIENCE
Fossil Fuel
Industry
Energy
Technology
Environmental
Conservation
Local
Global
Where I kind of fit in…
National
Security
The
Media
Economics
Ethics
CLIMATE
SCIENCE
Politics
Energy
Technology
Environmental
Conservation
My expertise is in the
science of climate change.
Fossilphysical
Fuel
Local
Industry
(oceans, atmosphere, sea ice, land hydrology…
Global
not economics, ecosystems, inter-generational ethics or politics)
But I can comment on some experiences concerning
communicating science info to people in other fields.
Some of what is beyond the scope of my expertise…
National
Security
The
Media
Economics
Ethics
The science
I speak of
does not include…
Politics
CLIMATE
SCIENCE
Energy
Technology
Environmental
Conservation
 determiningFossil
what
is an “unacceptable” or
Fuel
Local
Industry
“dangerous” amount of climate change.
Global
 prescribing when & which human responses
should be taken.
People get their climate science info via the media,
who in turn get their info from various sources
The
The volume of climate change
info being reported
Media
National
has increased
in recent
months,
Economicsbut has the
Security
“signal to noise ratio”
of the science content improved?
Ethics
CLIMATE
SCIENCE
Politics
Energy
Technology
Environmental
Conservation
vs. The Scientist as an “Advocate” (of policy, etc.)
Goal: using science to promote a particular downstream effect.
Fossil Fuel
Industry
Local
vs. The Non-scientistGlobal
presenting scientific info
vs. The Misinformer with or without scientific credentials
Goal: misrepresenting science to promote a particular downstream effect.
International Scientific Consensus…
Intergovernmental Panel on
Climate Change (IPCC)
WG1 Summary for
Policymakers released
2 Feb 2007
600 authors from 40
countries. Over 620 expert
reviewers and
a large number of
government reviewers
(~133 nations).
4th: 2007
3rd: 2001
2nd: 1995
1st: 1990
IPCC WG2 = Impacts; IPCC WG3 = Mitigation
http://www.ipcc.ch/SPM2feb07.pdf
http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
Most climate change discussions focus on
changes in surface climate…
commonly, global surface air temperature
Most climate change discussions focus on
changes in surface climate…
commonly, global surface air temperature
Most climate change discussions focus on
changes in surface climate…
commonly, global surface air temperature
“Warming of the climate system is unequivocal,
as is now evident from observations of increases
in global average air and ocean temperatures,
widespread melting of snow and ice, and
rising global average sea level.”
- IPCC AR4 WG1 SPM, Feb 07
Most climate change discussions focus on
changes in surface climate…
commonly, global surface air temperature
“Warming
theobserved
climate increase
system is in
unequivocal,
“Most ofofthe
globally
as is nowtemperatures
evident from since
observations
of increases
th century
averaged
the mid-20
in
average
ocean temperatures,
is global
very likely*
dueair
to and
the observed
increase in
widespread greenhouse
melting of snow
and ice, and
anthropogenic
gas concentrations.”
rising
level.”
(*veryglobal
likely =average
90-95% sea
certainty)
IPCC AR4
AR4 WG1
WG1 SPM, Feb 07
-- IPCC
Most climate change discussions focus on
changes in surface climate…
commonly, global surface air temperature
“Continued
emissions
at or above
“Most of greenhouse
the observedgas
increase
in globally
th century
current temperatures
rates would cause
warming
and
averaged
sincefurther
the mid-20
induce
changes
global climate
is verymany
likely*
due to in
thethe
observed
increasesystem
in
during the 21stgreenhouse
century thatgas
would
very likely be
anthropogenic
concentrations.”
= 90-95%
certainty)
larger than (*very
those likely
observed
during
the 20th century.”
(*very likely = 90-95% certainty)- -IPCC
IPCCAR4
AR4WG1
WG1SPM,
SPM,Feb
Feb0707
The International IPCC & US CCSP
(http://www.ipcc.ch)
The IPCC is the biggest, but not the only
science-based climate assessment game in town…
The US CCSP is a presidential
initiative that seeks to integrate
federal research on climate
change. More than 20 synthesis &
assessment reports on key topics
relevant to decision makers are
planned.
Joint Statement on Climate Change
Eleven National Science Academies - 2005
(including all members of the Group of Eight industrial powers)
Their role is to inform & advise.
"Climate change is real. There will always be
uncertainty in understanding a system as complex
as the world’s climate. However there is now strong
evidence that significant global warming is
occurring. … It is likely that most of the warming in
recent decades can be attributed to human
activities. ... The scientific understanding of climate change is
now sufficiently clear to justify nations taking prompt action. It is vital
that all nations identify cost-effective steps that they can take now,
to contribute to substantial and long-term reduction in net global
greenhouse gas emissions.” http://nationalacademies.org/onpi/06072005.pdf
Joint Statement on Climate Change
Eleven National Science Academies - 2005
(including all members of the Group of Eight industrial powers)
Their role is to inform & advise.
"Climate change is real. There will always be
uncertainty in understanding a system as complex
as the world’s climate. However there is now strong
evidence that significant global warming is
occurring. … It is likely that most of the warming in
recent decades can be attributed to human
activities. ... The scientific understanding of climate change is
now
clear to
justify nations
taking prompt
action.
It is vital
Theirsufficiently
physical science
statements
are consistent
with what
I present
here.
that
all
nations
identify
cost-effective
steps
that
they
can
take
now,
I don’t
comment
on the policy
bits
they cover...
It’s beyond
expertise
to
contribute
to substantial
and
long-term
reduction
in netmy
global
and not my role.
greenhouse
gas emissions.” http://nationalacademies.org/onpi/06072005.pdf
← If you’re in the DC area, check out this museum.
(http://www.koshland-science-museum.org/exhibitgcc )
http://www.ametsoc.org/policy/2007climatechange.html
Important Climate
Science Questions
1. Is Earth’s climate changing?
2. If so, what is causing the changes?
3. Will the climate change during the
21st century (and beyond)?
A Synthesis of Observations, Theory
and Numerical Modeling
The Climate Model Knowledge Cycle
THEORY
Knowledge &
Understanding
Model Development
OBSERVATIONS
Analysis of
Model Results
Well Designed
Model Experiments
Current model resolution
1980s
Atmosphere 2 deg.
1990s
2000s
OCEAN MODEL RESOLUTION: 1 deg.
What is a State-of-the-Art
Global Climate Model?
The four
physical
climate
components
The Next
Generation:
Earth
System
Model
Atmospheric GCM
Sea ice model
Ocean GCM
Land physics
and hydrology
Atmospheric GCM
Tracer transport and chemistry
Ocean ecology and
biogeochemistry
Sea ice model
Ocean GCM
Land ecology and
biogeochemistry
Land physics
and hydrology
Adding interactive Carbon and Nitrogen Cycling, etc.
1. Is Earth’s climate changing?
2. What is causing the changes?
Questions of Detection and Attribution:
Detection: establishing that an observed change
is significantly different than can be explained by
internal variability (separating signal from the noise).
Attribution: establishing cause and effect, and
assessing alternative hypotheses.
1. Is Earth’s climate changing?
Looking Back:
Past climate variability & change –
an issue of Detection
From the 2007 Intergovernmental Panel on
Climate Change Report (WG1):
“Warming of the climate system is unequivocal,
as is now evident from observations of increases
in global average air and ocean temperatures,
widespread melting of snow and ice, and
rising global average sea level.”
2. What is causing the changes?
A question of Attribution:
From the 2007 Intergovernmental Panel on
Climate Change Report (WG1):
“Most of the observed increase in globally
averaged temperatures since the mid-20th century
is very likely* due to the observed increase in
anthropogenic greenhouse gas concentrations.”
*very likely = 90-95% certainty
2. What is causing the
changes?
Carbon
Dioxide
Observational
Evidence for
Greenhouse
Gas Increases:
Methane
Nitrous
Oxide
Variations of the Earth’s Surface Temperature
Global surface temperatures over the past 140 years
Plateau
Late century
warming
Early century
warming
(Graph shows temperature changes relative to the 1961-1990 average in oC.
Multiply by 1.8 to convert to oF.)
2. What is causing the changes?
Variations of the Earth’s Surface Temperature
Observed Global Surface Temperatures
* Well-mixed greenhouse gases (CO2,
CH4, N2O, CFCs { F11, F12, F113, F22})
* Stratospheric O3, * Tropospheric O3
* Tropospheric Aerosols: [Sulfate, Black
and Organic Carbon], [Dust and Sea-salt];
* Land-use change (Hurtt et al.)
* Solar irradiance variations (Lean et al.)
* Volcanic aerosols (Ramachandran et al.,
Sato et al.)
2. What is causing the changes?
Variations of the Earth’s Surface Temperature
Observed Global Surface Temperatures
Model with D Greenhouse Gases Only (n=3)
Model forced only by smoothly varying GHGs yields
temperature response that’s smoother than the observed.
(this was characteristic of models of the ’80s and early ’90s)
* Well-mixed greenhouse gases (CO2, CH4, N2O, CFCs { F11, F12, F113, F22})
* Stratospheric O3, * Tropospheric O3
* Tropospheric Aerosols: [Sulfate, Black and Organic Carbon], [Dust and Sea-salt];
* Land-use change (Hurtt et al.)
* Solar irradiance variations (Lean et al.)
* Volcanic aerosols (Ramachandran et al., Sato et al.)
2. What is causing the changes?
Variations of the Earth’s Surface Temperature
Observed Global Surface Temperatures
Model with Natural Forcings Only
(solar + volcanic, n=3)
Model with Natural Forcings is
consistent with obs until ~1960…
…but can not
explain
late-century
warming
2. What is causing the changes?
Variations of the Earth’s Surface Temperature
Observed
Observed Global
Global Surface
Surface Temperatures
Temperatures
“All-Forcings” Model Results (n=5):
(7 GHGs, solar, volcanic, multiple
aerosols, land use changes)
Considering all of
these different
“forcings”(Natural &
Anthropogenic) the
model gets both
the magnitude of
the warming & the
decade variations
“about right”
Global Surface Air Temperatures
Goldilocks’ & The 3 Bears Attribution Conclusions:
• If we consider only the natural forcings (solar and
volcanic), the climate simulation is too cold (don’t have
the late 20th century warming signal).
•If we consider only the GHGs, the climate
simulation gets too hot too fast.
•Considering together various types of
forcing changes (natural & humaninduced) the model’s 20th century
global average temperature
simulations are just about right.
(1) GHGs (warming) (2) Solar(+/-)
(3) Volcanic (cooling)
(4) Tropospheric Aerosols (pollutants)
(+&-, net -, short lived)
Global Surface Air Temperatures
Goldilocks’ & The 3 Bears Attribution Conclusions:
• The simplified explanation presented here is
meant to illustrate the Detection/Attribution process.
In reality, much more detailed analysis (with some
sophisticated statistical methodologies) have been
performed using…
• Results from several modeling
research centers
• Looking at 4-D atmospheric
temperatures (regional, vertical)
• Similar studies have also
looked multiple climate variables,
including ocean heat content
(80-90% of the heat gained in
the past century resides in the
ocean)
Global Surface Air Temperatures
Goldilocks’ & The 3 Bears Attribution Conclusions:
• The simplified explanation presented here is
meant to illustrate the Detection/Attribution process.
In reality, much more detailed analysis (with some
sophisticated statistical methodologies) have been
performed using…
• Results from several modeling
research centers
• Looking at 4-D atmospheric
temperatures (regional, vertical)
• Similar studies have also
looked multiple climate variables,
including ocean heat content
(80-90% of the heat gained in
the past century resides in the
ocean)
Global Surface Air Temperatures
Goldilocks’ & The 3 Bears Attribution Conclusions:
• The simplified explanation presented here is
meant to illustrate the Detection/Attribution process.
In reality, much more detailed analysis (with some
sophisticated statistical methodologies) have been
performed using…
• Results from several modeling
research centers
• Looking at 4-D atmospheric
temperatures (regional, vertical)
• Similar studies have also
looked multiple climate variables,
including ocean heat content
(80-90% of the heat gained in
the past century resides in the
ocean)
Global Surface Air Temperatures
Goldilocks’ & The 3 Bears Attribution Conclusions:
• The simplified explanation presented here is
meant to illustrate the Detection/Attribution process.
In reality, much more detailed analysis (with some
sophisticated statistical methodologies) have been
performed using…
• Results from several modeling
research centers
• Looking at 4-D atmospheric
temperatures (regional, vertical)
• Similar studies have also
looked multiple climate variables,
including ocean heat content
(80-90% of the heat gained in
the past century resides in the
ocean)
Ocean Heat Content
(ANTHRO includes WMGGO3 & AEROSOL)
References:
• Delworth, T. L., V. Ramaswamy, and G. L. Stenchikov, 2005: The
impact of aerosols on simulated ocean temperature and heat
content in the 20th century. Geophysical Research Letters, vol 32.
• Levitus, S., J. I. Antonov, J. Wang, T. L. Delworth, K. W. Dixon, and A.
J. Broccoli, 2001. Anthropogenic warming of Earth's climate
system. Science, 292(5515), 267-270. [ONE PAGE SUMMARY]
GFDL Model results
2 meters
The upper 2 meters of the ocean
contains as much heat energy as
does the entire column of air above.
Schematic of 3-D Ocean Circulation
After Gnanadesikan & Hallberg, 2002
Drake
Passage
S
N
Simulated Ocean Heat Content Changes
Simulated
Surface Air
Temperature
Response
vs.
Simulated
Ocean Heat
Uptake
Response
Simulated Global Avg. Surface Air
Temperature Response
The “full” model (one with a dynamical ocean
model component and realistic bathymetry)
Simulated Global Avg. Surface Air
Temperature Response
Time Lag
Warming
Commitment
The “full” model (one with a dynamical ocean
model component and realistic bathymetry)
The mixed-layer ocean model
(the ocean is only 50m deep )
• ‘Global Warming’ is not globally uniform.
• The 3-D ocean plays an important role in
influencing both the rate of global surface air
temperature warming –and- the geographic
patterns of surface warming.
• The ocean’s “thermal inertia” is largely due to its
high heat capacity and its deep vertical mixing…
the ocean sequesters “greenhouse heat” (~80+%).
• Model simulations suggest that a significant
fraction of the ocean heat
content increase is
occurring in regions and
depths that have not been
well-observed in the past.
3. Will the climate change in
the 21st Century and beyond?
From the 2007 Intergovernmental Panel on
Climate Change (IPCC) Report:
“Continued greenhouse gas emissions at or above
current rates would cause further warming and
induce many changes in the global climate system
during the 21st century that would very likely be
larger than those observed during the 20th century.”
*very likely = 90-95% certainty
… But what about the uncertainties?
Prediction vs. Projection
http://sciencepolicy.colorado.edu/zine/archives/1-29/26/guest.html
Prediction versus Projection – Forecast versus Possibility
Mike MacCracken U.S. Global Change Research Program
A prediction is a probabilistic statement that something will
happen in the future based on what is known today. A
prediction generally assumes that future changes in related
conditions will not have a significant influence. In this sense, a
prediction is most influenced by the “initial conditions”.
In contrast to a prediction, a projection specifically allows for
significant changes in the set of "boundary conditions" that might
influence the prediction, creating "if this, then that" types of
statements. Thus, a projection is a probabilistic statement that
it is possible that something will happen in the future if
certain conditions develop. The set of time-varying
“boundary conditions” that is used in conjunction with making a
projection is often called a scenario, and each scenario is based
on assumptions about how the future will develop.
Prediction vs. Projection
http://sciencepolicy.colorado.edu/zine/archives/1-29/26/guest.html
Prediction versus Projection – Forecast versus Possibility
Mike MacCracken U.S. Global Change Research Program
A prediction is a probabilistic statement that something will
happen in the future based on what is known today. A
prediction generally assumes that future changes in related
conditions will not have a significant influence. In this sense, a
prediction is most influenced by the "initial conditions“.
In contrast to a prediction, a projection specifically allows for
significant changes in the set of "boundary conditions" that might
influence the prediction, creating "if this, then that" types of
statements. Thus, a projection is a probabilistic statement that
it is possible that something will happen in the future if
certain conditions develop. The set of boundary conditions that
is used in conjunction with making a projection is often called a
scenario, and each scenario is based on assumptions about how
the future will develop.
3. Will the climate change in
the 21st Century and beyond?
From the 2007 Intergovernmental Panel on
Climate Change (IPCC) Report:
“Continued greenhouse gas emissions at or above
current rates would cause further warming and
induce many changes in the global climate system
during the 21st century that would very likely be
larger than those observed during the 20th century.”
*very likely = 90-95% certainty
… But what about the uncertainties?
Uncertainties In Climate Change
Projections
Two broad types of uncertainties:
1) What will be the future concentrations of
greenhouse gases in the atmosphere?
(depends on population size, economic growth,
energy use efficiency and development of
alternative energy sources)
2) How will the climate system respond to the
changes in greenhouse gases?
(the computer models are incomplete &
are not perfect)
Model projections
following 3 different
“If…Then” 21st cent.
9F
emissions scenarios
and the
“Committed Climate
Change” scenario.
--- 4.5F
Shaded areas show
+/- 1 std. dev.
of model runs.
0F
T=PxGxExC+d
T: Total annual greenhouse gas emission rate
P: Population size
G: per capita Gross Domestic Product $
E: Energy use per $ of GDP
C: GHG emissions per unit energy use
d: Deforestation effects
* And since most of the major anthropogenic greenhouse
gases stay in the atmosphere for several years to more
than a century, where they enter the atmosphere doesn’t
matter to the climate system.
Uncertainties In Climate Change
Projections
The smaller the spatial scale, the
greater the uncertainty.
In other words, we have more confidence in
projections about how the climate may
change over large areas (for example, the
Arctic vs. the tropics… temperatures over
mid-latitude oceans vs. mid-latitude land)
than we do for individual states or
congressional districts.
Uncertainties In Climate Change
Projections
The smaller the spatial scale, the
greater the uncertainty.
Implications: People (scientists, policymakers,
the general public) tend to place global warming on
their “radar screens” on the basis of convincing
physical science evidence on the global and very
large scale – the scales that we have the most
confidence in.
However, once climate change is a matter they give
attention to, most people then ask about smaller
scale impacts (and not just the physical climate).
•
GFDL CM2.1 model-simulated change in seasonal mean surface air temperature from the late 20th century (1971-2000
average) to the middle 21st century (2051-2060). The left panel shows changes for June July August (JJA) seasonal
averages, and the right panel shows changes for December January February (DJF). The simulated surface air temperature
changes are in response to increasing greenhouse gases and aerosols based on a "middle of the road" estimate of future
emissions known as IPCC SRES A1B. Warming is projected to be larger over continents than oceans, and is largest at high
latitudes of the Northern Hemisphere during Northern Hemisphere winter.
Will the Wet Get Wetter & The Dry Drier?
Will the Wet Get Wetter & The Dry Drier?
Communication Challenges?
Sea Level Rise In a Warming World
One can read about the
implications of sea level
rise on US infrastructure
in the popular press…
Some of which may not
sufficiently distinguish
between persistent
innundation due to longterm sea level rise vs.
flooding during storm surges
and high tides on top of
sea level rise.
A once in 100 year flooding
event may become a once in
50 yr or 20 yr or 5 yr event…
Paraphrasing the IPCC AR4 Working Group 1
Summary For Policymakers (Feb. 2007)
• Ocean warming and sea level rise will
continue for centuries.
Long time scales … like turning
around a supertanker
• Ice flow dynamics could increase the
vulnerability of the ice sheets to warming,
increasing future sea level rise.
However, understanding of these ice
sheet processes is limited.
The 2 Major Reasons for
Global Sea Level Change
1) Because ocean water expands when it warms.
Our climate models directly simulate the thermal
expansion effect.
2) Because land ice is adding water to the ocean.
Our climate models only estimate the land ice effect.
Reducing sea level projection
uncertainties requires
improvements in scientific
understanding & a commitment
of computer modeling resources.
In other words,
A Synthesis of Observations, Theory & Modeling.
NASA graphic
24”
12”
0”
COMMITTED CHANGE
A Single GFDL CM2.1 Coupled Climate Model Projection
SRES A1B CHANGE
The Science of Sea Level Rise
In a Warming World
Attribution across the scales of climate
Q: What does the above
statement that appeared in
the Boston Globe’s opinion
section have in common
with…
Attribution across the scales of climate
Research [...] currently in
press with the Journal of
Climate, describes the
tropical multi-decadal
signal and shows that it
accounts for the entire
inter-related set of
conditions that controls
hurricane activity for
decades at a time."
Attribution across the scales of climate
A: They both assert with 100% certainty
that hurricane events in the Atlantic
are either entirely due to
anthropogenic climate change or have
absolutely nothing to do with humaninduced climate change.
The level of uncertainty for this topic is such that a forecast
of either 0% or 100% probability is irresponsible.
Forest fires occur due to natural causes
(e.g., lightning), otherwise there would be no forest fires
in uninhabited areas, past or present.
• So does the fact that forest fires occur naturally mean
that Smokey is a liar, and that people can not cause
forest fires?
• Or conversely, if Smokey’s right, then are all forest
fires a result of humans?
Is the problem that statement like this…
• no one specific weather event, such as [this recent spell of
warm weather in the East], can be uniquely attributed
directly to global warming.
…is misinterpreted as being equivalent to…
• no one specific weather event, such as [this recent spell of
warm weather in the East], can be uniquely attributed
directly to global warming, and therefore we can say it is
entirely unrelated to global warming.
If that is the case, then there are analogies
that might help reinforce the distinction.
”It's very dangerous to blame climate for
weather," says Richard Alley, a professor of
geosciences at Penn State University.
But he doesn't let climate change off the hook
when discussing our warm winter.
"No, we didn't cause it, but we made it more
likely," he concludes. It's like rolling loaded
dice in a craps game.
Natural modulation
of ENSO
in a 2000yr
coupled GCM run
Annual Cycle
}
ENSO (somewhat
irregular period)
Courtesy Andrew Wittenberg, NOAA/GFDL
Natural modulation
of ENSO
in a 2000yr
coupled GCM run
2000 yr & 400 yr means
100 yr means
25 yr means
}
Courtesy Andrew Wittenberg, NOAA/GFDL
Natural modulation
of ENSO
in a 2000yr
coupled GCM run
2000 yr & 400 yr means
100 yr means
25 yr means
~ length of satellite record
Courtesy Andrew Wittenberg, NOAA/GFDL
Decadal Atlantic MOC Predictability
Building some small ensembles by tweaking initial conditions:
The CM2.1 model produces a separate restart file for
each of its 4 main subcomponents.
In our first line of inquiry, we generated ensembles
of 20 year long runs by mixing atmospheric restarts
drawn from days >5 days and < 1 month from the
1 Jan initialization used for the ocean, land &
sea ice restarts.
For example…
ocean
land
sea ice
1 Jan 1001
generating a ten
member ensemble
atmos
07 Dec 1000
12 Dec 1000
17 Dec 1000
22 Dec 1000
27 Dec 1000
06 Jan 1001
11 Jan 1001
16 Jan 1001
21 Jan 1001
26 Jan 1001
?? Will the ensemble members suggest Atl. MOC
predictability exists over periods of a decade or longer…
…or not? And why?
Regarding communication of
climate change projections…
In addition to longer term
trend estimates with ranges 
And statements such
For the next two decades, a warming of
about 0.2°C per decade is projected for a
range of SRES emission scenarios. Even
if the concentrations of all greenhouse
gases and aerosols had been kept
constant at year 2000 levels, a further
warming of about 0.1°C per decade
would be expected… (IPCC AR4 SPM)
Might it be valuable to convey information about the
possibility of short term (~5-10 yr) cooling or greater short
term warming rates that would not be inconsistent with
these results? (more so at smaller spatial scales).
[analogous to 30%POP forecast?]
SUMMARY
The strong scientific consensus is that we are
seeing more signs that human caused climate
change is real and that change will become
more rapid in the coming century.
However…
• Need to think in terms of projection possibilities, not
detailed, localized certainties.
• We still have a lot to learn about how the climate system
works.
• As models become more sophisticated, they will include
more climate system feedbacks (+ & -).
• More work will be required to narrow the range of
uncertainties about the future spatial and temporal
evolution of climate.
• In addition to more knowledge of the climate system,
developing more skill at smaller spatial scales will require
more computer power.
On the science side, the continued synthesis of
observations, theory and modeling will help separate
the signal from the noise.
Computer Modeling of the
Global Climate & its Role in the
Assessment of Climate Change
Keith W. Dixon
research meteorologist
NOAA / Geophysical Fluid Dynamics Laboratory
Princeton, NJ
NROW IX
Albany, New York
7 Nov 2007
Projections of Future Changes in Climate
• For the next two decades a warming of about 0.2°C per
decade is projected for a range of SRES emission
scenarios.
• Even if the concentrations of all greenhouse gases and
aerosols had been kept constant at year 2000 levels, a
further warming of about 0.1°C per decade would be
expected.
• Earlier IPCC projections of 0.15 to 0.3 oC per decade can
now be compared with observed values of 0.2 oC
Projections of Future Changes in Climate
There is now higher confidence in projected patterns
of warming and other regional-scale features, including
changes in wind patterns, precipitation, and some
aspects of extremes and of ice.
PROJECTIONS OF FUTURE CHANGES IN CLIMATE
• Snow cover is projected to contract
• Widespread increases in thaw depth most permafrost
regions
• Sea ice is projected to shrink in both the Arctic and
Antarctic
• In some projections, Arctic late-summer sea ice
disappears almost entirely by the latter part of the 21st
century
PROJECTIONS OF FUTURE CHANGES IN CLIMATE
• Very likely that hot extremes, heat waves, and heavy
precipitation events will continue to become more
frequent
• Likely that future tropical cyclones will become more
intense, with larger peak wind speeds and more heavy
precipitation
 less confidence in decrease of total number
• Extra-tropical storm tracks projected to move poleward
with consequent changes in wind, precipitation, and
temperature patterns
PROJECTIONS OF FUTURE CHANGES IN CLIMATE
• Based on current model simulations, it is very likely that
the meridional overturning circulation (MOC) of the
Atlantic Ocean will slow down during the 21st century.
 longer term changes not assessed with confidence
• Temperatures in the Atlantic region are projected to
increase despite such changes due to the much larger
warming associated with projected increases of
greenhouse gases.
PROJECTIONS OF FUTURE CHANGES IN CLIMATE
• Anthropogenic warming and sea level rise would continue
for centuries due to the timescales associated with climate
processes and feedbacks, even if greenhouse gas
concentrations were to be stabilized.
• Temperatures in excess of 1.9 to 4.6°C warmer than preindustrial sustained for millennia…eventual melt of the
Greenland ice sheet. Would raise sea level by 7 m.
Comparable to 125,000 years ago.