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

Computer Modeling of the Computer Modeling of the Global Climate & its Role in the Global Climate & its Role in the Assessment of Climate ChangeAssessment of Climate Change

Keith W. Dixonresearch meteorologist

NOAA / Geophysical Fluid Dynamics LaboratoryPrinceton, NJ

NROW IXNROW IXAlbany, New YorkAlbany, New York

7 Nov 20077 Nov 2007

My BackgroundMy 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: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: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/highlightshttp://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 Media Coverage of Climate Change IssueClimate Change Issue

“Climbing temperatures. Melting glaciers.Rising seas. All over the earth we’refeeling the heat. Why isn’t Washington?”

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 MagazineApril 9, 2001




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.

Not a SCIENTIFIC QUESTION, so I’m not going there in this talk!





Though a political consensus may not exist in the US, the strongstrong scientific consensusscientific consensus is that we are seeing more signs that human-caused climate change is real and that change will become more rapid.


Fermenting Froth vs. Scientific ConsensusSources 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)

NationalSecurity

Ethics

Politics

Fossil FuelIndustry

GlobalLocal

EnvironmentalConservation

EnergyTechnology

Economics

TheMedia

CLIMATECLIMATESCIENCESCIENCE

Differentcost/benefitanalyses aredone by thosewith thesedifferent perspectives,but all arelinked to theunderlyingclimate science.

Climate Change: A Matter of Contending PerspectivesClimate Change: A Matter of Contending Perspectives (after Mike MacCracken)

NationalSecurity

Ethics

Politics

Fossil FuelIndustry

Global

Local


EnergyTechnology

Economics

TheMedia


My expertise is in the physical science of climate change.My expertise is in the physical science of climate change.(oceans, atmosphere, sea ice, land hydrology…

not economics, ecosystems, inter-generational ethics or politics)But I can comment on some experiences concerning But I can comment on some experiences concerning communicating science info to people in other fields.communicating science info to people in other fields.

Where I kind of fit in…

NationalSecurity

Ethics

Politics

Fossil FuelIndustry

Global

Local


EnergyTechnology

Economics

TheMedia


determining what is an “unacceptable” or “dangerous” amount of climate change. prescribing when & which human responses should be taken.

The scienceI speak ofdoes not include…

Some of what is beyond the scope of my expertise…

NationalSecurity

Ethics

Politics

Fossil FuelIndustry

Global

Local


EnergyTechnology

Economics

TheMedia


The volume of climate change info being reportedhas increased in recent months, but has the

“signal to noise ratio” of the science content improved?

vs. The Scientist as an “Advocate” (of policy, etc.)Goal: using science to promote a particular downstream effect.

vs. The Non-scientist presenting scientific info

vs. The Misinformer with or without scientific credentialsGoal: misrepresenting science to promote a particular downstream effect.

People get their climate science info via the media, who in turn get their info from various sources

International Scientific Consensus…International Scientific Consensus…

Intergovernmental Panel on Intergovernmental Panel on Climate Change (IPCC)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: 20073rd: 20012nd: 19951st: 1990

http://www.ipcc.ch/SPM2feb07.pdfhttp://ipcc-wg1.ucar.edu/wg1/wg1-report.html

IPCC WG2 = Impacts; IPCC WG3 = Mitigation

Most climate change discussions Most climate change discussions focus on changes in surface climate…focus on changes in surface climate…commonly, global surface air temperaturecommonly, 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- IPCC AR4 WG1 SPM, Feb 07


“Warming of the climate system is unequivocal, as is now evident from observations of increases


rising global average sea level.” - IPCC AR4 WG1 SPM, Feb 07

“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) - IPCC AR4 WG1 SPM, Feb 07


“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) - IPCC AR4 WG1 SPM, Feb 07

“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) - IPCC AR4 WG1 SPM, Feb 07

The International IPCC & US CCSP

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.

(http://www.ipcc.ch)

Joint Statement on Climate ChangeJoint Statement on Climate ChangeEleven National Science Academies - 2005Eleven 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 ChangeJoint Statement on Climate ChangeEleven National Science Academies - 2005Eleven 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

← If you’re in the DC area, check out this museum.(http://www.koshland-science-museum.org/exhibitgcc )

Their physical science statements are consistent with what I present here.I don’t comment on the policy bits they cover... It’s beyond my expertise and not my role.

http://www.ametsoc.org/policy/2007climatechange.html

Important Climate Important Climate Science QuestionsScience Questions

1.1. Is Earth’s climate changing?Is Earth’s climate changing?

2.2. If so, what is causing the changes?If so, what is causing the changes?

3.3. Will the climate change during the Will the climate change during the 21 21stst century (and beyond)? century (and beyond)?A Synthesis of Observations, TheoryA Synthesis of Observations, Theory

and Numerical Modelingand Numerical Modeling

The Climate Model Knowledge CycleThe Climate Model Knowledge Cycle

Knowledge & Understanding

Model Development

OBSERVATIONS

THEORY

Well DesignedModel Experiments

Analysis ofModel Results

Current model resolution

OCEAN MODEL RESOLUTION: 1 deg.

1980s

1990s

2000s

Atmosphere 2 deg.

What is a State-of-the-Art What is a State-of-the-Art Global Climate Model?Global Climate Model?

The four physical climate

componentsLand physicsand hydrology

Ocean GCM

Atmospheric GCM

Land physicsand hydrology

Ocean ecology andbiogeochemistry

Atmospheric GCM

Tracer transport and chemistry

Land ecology andbiogeochemistry

Sea ice model

Ocean GCM

Sea ice model

The Next Generation:

Earth

System

Model

Adding interactive Carbon and Nitrogen Cycling, etc.

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.

2. What is causing the changes?What is causing the changes?

1. Is Earth’s climate changing?Is Earth’s climate changing?

From the 2007 Intergovernmental Panel on Climate Change Report (WG1):

Looking Back: Looking Back: Past climate variability & change – Past climate variability & change –

an issue of Detectionan issue of Detection

1. Is Earth’s climate changing?Is Earth’s climate changing?

““Warming of the climate system is unequivocal, as is now evident from observations of increases


rising global average sea level.”.”

A question of Attribution:


From the 2007 Intergovernmental Panel on Climate Change Report (WG1):

““MostMost of the observed increase in globally of the observed increase in globally averaged temperatures since the mid-20averaged temperatures since the mid-20thth century century

is is very likelyvery likely** due to the observed increase in due to the observed increase in anthropogenic greenhouse gas concentrations.”anthropogenic greenhouse gas concentrations.”

*very likely = 90-95% certainty*very likely = 90-95% certainty

2. What is causing the What is causing the changes?changes?

ObservationalEvidence for Greenhouse

Gas Increases:

Carbon Dioxide

Methane

NitrousOxide

Variations of the Earth’s Surface TemperatureVariations of the Earth’s Surface Temperature

(Graph shows temperature changes relative to the 1961-1990 average in oC. Multiply by 1.8 to convert to oF.)

Global surface temperatures over the past 140 years

Early centurywarming

Plateau

Late centurywarming


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.)



Model with Greenhouse Gases Only (n=3)


Model forced only by smoothly varying GHGs yieldstemperature 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.)





Model with Natural Forcings Only(solar + volcanic, n=3)

…but can notexplain

late-centurywarming

Model with Natural Forcings is consistent with obs until ~1960…




Observed Global Surface 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 boththe magnitude of

the warming & thedecade 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 & human-induced) 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 TemperaturesGoldilocks’ & The 3 Bears Attribution Conclusions:

• The simplified explanation presented here ismeant to illustrate the Detection/Attribution process.In reality, much more detailed analysis (with somesophisticated statistical methodologies) have beenperformed using…• Results from several modelingresearch centers• Looking at 4-D atmospherictemperatures (regional, vertical)• Similar studies have alsolooked multiple climate variables,including ocean heat content(80-90% of the heat gained inthe past century resides in theocean)

Ocean Heat Content

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]

(ANTHRO includes WMGGO3 & AEROSOL)

GFDL Model results

2 m

ete

rs

The upper 2 meters of the oceancontains as much heat energy asdoes the entire column of air above.

Schematic of 3-D Ocean Schematic of 3-D Ocean CirculationCirculation

After Gnanadesikan & Hallberg, 2002

DrakePassage

S N

Simulated Ocean Heat Content ChangesSimulated Ocean Heat Content Changes

Simulated Simulated Surface Air Surface Air TemperaturTemperature Responsee Response

vs.vs.

Simulated Simulated Ocean Heat Ocean Heat

Uptake Uptake ResponseResponse

Simulated Global Avg. Surface Simulated Global Avg. Surface Air Temperature ResponseAir Temperature Response

The “full” model (one with a dynamical oceanmodel component and realistic bathymetry)

Warm

ing

Co

mm

itmen

t

The “full” model (one with a dynamical oceanmodel component and realistic bathymetry)

The mixed-layer ocean model (the ocean is only 50m deep )

Simulated Global Avg. Surface Simulated Global Avg. Surface Air Temperature ResponseAir Temperature Response

Time Lag

• ‘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.

… But what about the uncertainties?

3. Will the climate change in Will the climate change in the 21the 21stst Century and beyond? 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


larger than those observed during the 20th century.”.”


Prediction Prediction vs.vs. Projection Projection

http://sciencepolicy.colorado.edu/zine/archives/1-29/26/guest.html

Prediction versus Projection – Forecast versus PossibilityPrediction versus Projection – Forecast versus PossibilityMike 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 Prediction vs.vs. Projection Projection

http://sciencepolicy.colorado.edu/zine/archives/1-29/26/guest.html

Prediction versus Projection – Forecast versus PossibilityPrediction versus Projection – Forecast versus PossibilityMike 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.

… But what about the uncertainties?

3. Will the climate change in Will the climate change in the 21the 21stst Century and beyond? Century and beyond?

From the 2007 Intergovernmental Panel on Climate Change (IPCC) Report:

““Continued greenhouse gas emissions at or above Continued greenhouse gas emissions at or above current ratescurrent rates would cause further warming and


larger than those observed during the 20th century.”.”


Uncertainties In Climate Change Uncertainties In Climate Change ProjectionsProjections

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 projectionsfollowing 3 different “If…Then” 21st cent. emissions scenarios

and the “Committed ClimateChange” scenario.

Shaded areas show +/- 1 std. dev.of model runs.

9F

0F

--- 4.5F

T = P x G x E x C + T = P x G x E x C + dd

TT: Total annual greenhouse gas emission rate

PP: Population size

GG: per capita Gross Domestic Product $

EE: Energy use per $ of GDP

CC: GHG emissions per unit energy use

dd: 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.


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.


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?

Communication Challenges?

One can read about theimplications of sea level rise on US infrastructurein the popular press…

Some of which may not sufficiently distinguish between persistentinnundation due to long-term sea level rise vs. flooding during storm surges and high tides on top of sea level rise.

A once in 100 year floodingevent may become a once in50 yr or 20 yr or 5 yr event…

Sea Level Rise In a Warming WorldSea Level Rise In a Warming World

Paraphrasing the IPCC AR4 Working Group 1 Paraphrasing the IPCC AR4 Working Group 1 Summary For Policymakers (Feb. 2007)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 The 2 Major Reasons for GlobalGlobal Sea Level Change 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.A Synthesis of Observations, Theory & Modeling.NASA graphic

The Science of Sea Level RiseThe Science of Sea Level RiseIn a Warming WorldIn a Warming World

0”

24”

12”

A Single GFDL CM2.1 Coupled Climate Model Projection

COM

MIT

TED

CHAN

GE

SRES

A1B

CHA

NGE

Q:Q: What does the above What does the above statement that appeared in statement that appeared in the Boston Globe’s opinion the Boston Globe’s opinion section have in common section have in common with…with…

Attribution across the scales of climateAttribution 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."

A:A: They both assert with 100% certainty They both assert with 100% certainty that hurricane events in the Atlantic that hurricane events in the Atlantic are either entirely due to are either entirely due to anthropogenic climate change or have anthropogenic climate change or have absolutely nothing to do with human-absolutely nothing to do with human-induced climate change.induced climate change.


The level of uncertainty for this topic is such that a forecastof 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?

• 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 the problem that statement like this…

…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.

”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.

If that is the case, then there are analogies that might help reinforce the distinction.

Natural modulationNatural modulationof ENSOof ENSO

in a 2000yrin a 2000yrcoupled GCM runcoupled GCM run

}Annual Cycle

ENSO (somewhatirregular period)

Courtesy Andrew Wittenberg, NOAA/GFDL

2000 yr & 400 yr means 100 yr means 25 yr means

}







2000 yr & 400 yr means 100 yr means 25 yr means ~ length of satellite record

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 ensemblesof 20 year long runs by mixing atmospheric restartsdrawn from days >5 days and < 1 month from the 1 Jan initialization used for the ocean, land & sea ice restarts. For example…

sea ice atmosocean land

Decadal Atlantic MOC Predictability

1 Jan 1001 06 Jan 100111 Jan 100116 Jan 100121 Jan 100126 Jan 1001

generating a ten member ensemble

07 Dec 100012 Dec 100017 Dec 100022 Dec 100027 Dec 1000

?? Will the ensemble members suggest Atl. MOCpredictability 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?]

SUMMARYSUMMARY

The strongstrong scientific consensusscientific 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…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 Computer Modeling of the Global Climate & its Role in the Global Climate & its Role in the Assessment of Climate ChangeAssessment of Climate Change

Keith W. Dixonresearch meteorologist

NOAA / Geophysical Fluid Dynamics LaboratoryPrinceton, NJ

NROW IXNROW IXAlbany, New YorkAlbany, New York

7 Nov 20077 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.

• 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 PROJECTIONS OF FUTURE CHANGES IN CLIMATE 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 CLIMATEPROJECTIONS 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 pre-industrial sustained for millennia…eventual melt of the Greenland ice sheet. Would raise sea level by 7 m. Comparable to 125,000 years ago.

PROJECTIONS OF FUTURE CHANGES IN CLIMATE

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