Global Warming (Thomas C. Peterson, Ph.D.)

8/7/2019 Global Warming (Thomas C. Peterson, Ph.D.)

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11Climate Change 101March 12, 2007

Thomas C. Peterson

NOAAs National Climatic Data CenterAsheville, North Carolina

Climate Change 101:

An Introduction to Climate

Change Science

Climate Change 101:

An Introduction to Climate

Change Science


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Outline of the talk: The nature of science The greenhouse effect

The physics of climate change

Global climate models Climate change detection and attribution

Common questions

Concluding comments


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The nature of science

. . . science, which I define as a set ofmethods designed to describe andinterpret observed or inferred phenomena,

past or present, and aimed at building atestable body of knowledge open torejection or confirmation. In other words,science is a specific way of analyzing

information with the goal of testing claims. Michael Shermer, director of Skeptics

Society, 1997


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Science is never 100% certain

Science does not deal in certainty, sofact can only mean a propositionaffirmed to such a high degree thatit would be perverse to withhold onesprovisional assent.

Stephen Jay Gould, geologist, 1999


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Science is self-correcting

In practice, contemporary scientistsusually submit their research findings

to the scrutiny of their peers, whichincludes disclosing the methods anddata which they use, so that theirresults can be checked through

replication by other scientists. IPCC 4th Assessment Report, 2007


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Competing claims, information, andeven misinformation can be assessed

Testability Can it be proved false?

Fruitfulness

Does it yield observable surprising predictions? Scope

How many different phenomena does it explain? Simplicity

How many assumptions does it make? Conservatism

Is it consistent with our well founded beliefs? Theodore Schick, Jr. & Lewis Vaughn, philosophers,

2001


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We need the greenhouse effect

The Earths surface temperature is~60F

Without the greenhouse effect itwould be ~5F

But humans are changing the radiativeproperties of the atmosphere andthereby the greenhouse effect


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Climate Forcing Summary

FromRavishankara (2006)

Warming versuscooling effectsare like the tortoise versusthe hare.


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Do you believe in globalwarming?

I believe in quantum physics.


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Quantum physics tells us that

Infrared (IR) energy can only be absorbedand radiated in very small particle-likepackets of energy called quanta


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Each molecule can absorb and radiatequanta at different wavelengths


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Two atom molecules can absorb very littleIR energy E.g., Nitrogen (N2) and Oxygen (O2)

98% of the atmosphere


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Two atom molecules can absorb very littleIR energy E.g., Nitrogen (N2) and Oxygen (O2)

98% of the atmosphere

Three or more atom molecules do absorband radiate in the IR E.g., Carbon Dioxide (CO2), water vapor (H2O),

methane (CH4) 2% of the atmosphere CO

2only 0.04% of the atmosphere


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Global climate models Computer

generatednumericalsimulations ofthe climate

system


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Climate change detection andattribution

Often linked together but are twoseparate processes

Very mathematically intensive Involves the temporal and spatial

patterns of climate change

So this description is quite simplified


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Climate change detection

Examine the instrumental temperature recordfor the last 100 years

Examine the paleoclimate record for the past

1000 or 2000 years Examine climate model control runs

No changes in forcing

Run for 10,000s of years

Is the recent observed climate change outsidethe bounds of natural climate variability?


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Yes, the recent observed climatechange is beyond the bounds of

natural variability


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Attribution: What is the cause of

the detected climate change? Attribution is primarily model based

analysis

What mix of forcings is required tocreate the detected climate change?


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Attribution example: Most of thewarming over the past 50 years is likely

due to greenhouse gas increases

IPCC TAR


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Are CO2 and other greenhousegasses really responsible for

changing the global temperature?

Quantum physics says we shouldexpect them to be


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Climate models say they are


changing the global temperature?


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changing the global temperature? Historical observations indicate they are

related


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changing the global temperature? Ice cores can give us the long view


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changing the global temperature? The long view says they are definitely related


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Common questions


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You cant predict the weather 10 days inadvance, how can you predict the climate

100 years from now? Weather forecasting

and climateprojections are verydifferent Weather forecasting

is primarily basedmovements andinteractions of

weather parameters Predicting a storm 1

day late is an error

Climate projections are primarily based onthe physics of long-term changes in solarenergy and infrared radiation

The same climate physics that allow us to100% accurately predict that next summerwill be warmer than next winter

After Kiehl and Trenberth (1997)


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Dont urban heat islands hot local temperaturescaused by buildings and concrete- make U.S. and

global temperatures unreliable?

No The urban effect is

minor with land data Ocean data has no

urban effect andshows warming Increasing

temperaturessupported by: plant bloom dates

Lake/riverfreeze/thaw dates

Glaciers melting Etc.Peterson and Owen (2005)


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Additional supporting evidence:the shrinking Arctic sea-ice


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Dont satellites show no warming?

One satellite data setdid several years ago

As another grouptried to reproduce it,an error in the dataprocessing wasdiscovered

Both satellite andsurface datacurrently showwarming


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What are the climateprojections for my area?

Models arent accurate at city level But can use projections for a large region

such as the Eastern US Projections are not from theIntergovernmental Panel on Climate Change(IPCC)

But based on all the models that were run

to contribute to the IPCC Over 25 models Three emission scenarios


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Precipitation


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Total precipitation:

From Peterson et al., 2007b

1 = ~68%2 = ~95%


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Precipitation projections:

Totalprecipitationvery uncertain

However,modelsproject heavy

precipitationwill increaseCreated for a report due to be released in late 2007.


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Temperature


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Low CO2 scenario



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Mid-range CO2 increases



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Business as usual CO2



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Temperature projections

Projections show more change in thefuture than recently observed

Even if we stopped emitting CO2 nowthere would still be warming for thenext few decades

How warm it will be 100 years fromnow is dependent on future emissionsof greenhouse gases


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Does anthropogenic globalwarming pass the rating criteria?

Testability Can it be proved false?

Yes, the last decade could have been cold, laboratory tests on CO2could have proven theory wrong

Fruitfulness Does it yield observable surprising predictions?

Yes, predicts increase in heavy precipitation which has beenobserved Scope

How many different phenomena does it explain? Changes in temperature, precipitation, atmospheric circulation,

storms, mountain glacier melting, arctic sea-ice melting, etc. Simplicity

How many assumptions does it make? None, based on quantum physics Conservatism

Is it consistent with our well founded beliefs? Yes, no previously unknown phenomena are required to explain it


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Ockhams razor

14th

Century English Franciscan friar andphilosopher William of Ockham developed thisprinciple: All things being equal, the simplest solution tends to

be the best one. Greenhouse gases warming the planet is simple Alternate climate change explanations are not

Require ignoring CO2s radiative effect Paying attention to unproven explanations

It is just part of a natural cycle (that doesnt show up in

the paleoclimate record) It is all due to changes in solar geomagnetism It is all due to urban contamination of data sets A negative feedback like the cloud-iris effect will save us It is all due to cosmic rays Etc.


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Final comment

Stepping out into record hot weather, afriend who is an expert on climate changedetection and attribution was asked if the

high temperatures they were experiencingwere due to global warming He responded:

You cant attribute any one days temperature

to global warming But unusually warm weather like that does giveus the privilege of experiencing the weather weare bequeathing our children and grandchildren


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Selected References

Kiehl, J., and K. Trenberth, 1997: Earths annual globalmean energy budget. Bull. Amer. Meteor. Soc., 78, 197-206.

Peterson, Thomas C. and Timothy W. Owen, 2005: Urban

Heat Island Assessment: Metadata are Important.Journal of Climate, 18, 2637-2646. Peterson, Thomas C., Xuebin Zhang, Manola Brunet India,

Jorge Luis Vzquez Aguirre, 2007a: Changes in NorthAmerican extremes derived from daily weather data.Proceedings of the National Academy of Science, inpreparation.

Peterson, Thomas C., Marjorie McGuirk, Tamara G.Houston, Andrew H. Horvitz and Michael F. Wehner,2007b: Climate Variability and Change with Implicationsfor Transportation, National Research Council, in press.


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Global Warming (Thomas C. Peterson, Ph.D.)