1 climate change 101march 12, 2007 thomas c. peterson noaa’s national climatic data center...
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11Climate Change 101March 12, 2007
Thomas C. Peterson
NOAA’s 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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22Climate Change 101March 12, 2007
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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33Climate Change 101March 12, 2007
The nature of science
• . . . science, which I define as a set of methods designed to describe and interpret observed or inferred phenomena, past or present, and aimed at building a testable body of knowledge open to rejection 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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44Climate Change 101March 12, 2007
Science is never 100% certain
• Science does not deal in certainty, so “fact” can only mean a proposition affirmed to such a high degree that it would be perverse to withhold one’s provisional assent.– Stephen Jay Gould, geologist, 1999
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55Climate Change 101March 12, 2007
Science is self-correcting
• In practice, contemporary scientists usually submit their research findings to the scrutiny of their peers, which includes disclosing the methods and data which they use, so that their results can be checked through replication by other scientists.– IPCC 4th Assessment Report, 2007
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66Climate Change 101March 12, 2007
Competing claims, information, and even 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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77Climate Change 101March 12, 2007
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88Climate Change 101March 12, 2007
We need the greenhouse effect
• The Earth’s surface temperature is ~60ºF
• Without the greenhouse effect it would be ~5ºF
• But humans are changing the radiative properties of the atmosphere and thereby the greenhouse effect
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99Climate Change 101March 12, 2007
Climate Forcing Summary
From Ravishankara (2006)
Warming versus cooling effects are like the tortoise versus the hare.
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1010Climate Change 101March 12, 2007
Do you believe in global warming?
• I believe in quantum physics.
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1111Climate Change 101March 12, 2007
Quantum physics tells us that• Infrared (IR) energy can only be absorbed
and radiated in very small particle-like packets of energy called quanta
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1212Climate Change 101March 12, 2007
Quantum physics tells us that• Infrared (IR) energy can only be absorbed
and radiated in very small particle-like packets of energy called quanta
• Each molecule can absorb and radiate quanta at different wavelengths
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1313Climate Change 101March 12, 2007
Quantum physics tells us that• Infrared (IR) energy can only be
absorbed and radiated in very small particle-like packets of energy called quanta
• Each molecule can absorb and radiate quanta at different wavelengths
• Two atom molecules can absorb very little IR energy– E.g., Nitrogen (N2) and Oxygen (O2)
• 98% of the atmosphere
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1414Climate Change 101March 12, 2007
Quantum physics tells us that• Infrared (IR) energy can only be absorbed
and radiated in very small particle-like packets of energy called quanta
• Each molecule can absorb and radiate quanta at different wavelengths
• Two atom molecules can absorb very little IR energy– E.g., Nitrogen (N2) and Oxygen (O2)
• 98% of the atmosphere
• Three or more atom molecules do absorb and radiate in the IR– E.g., Carbon Dioxide (CO2), water vapor
(H2O), methane (CH4)• 2% of the atmosphere• CO2 only 0.04% of the atmosphere
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1515Climate Change 101March 12, 2007
Global climate models• Computer
generated numerical simulations of the climate system
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1616Climate Change 101March 12, 2007
Climate change detection and attribution
• Often linked together but are two separate processes
• Very mathematically intensive– Involves the temporal and spatial
patterns of climate change– So this description is quite simplified
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1717Climate Change 101March 12, 2007
Climate change detection
• Examine the instrumental temperature record for 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 outside the bounds of natural climate variability?
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1818Climate Change 101March 12, 2007
Yes, the recent observed climate change is beyond the bounds of
natural variability
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1919Climate Change 101March 12, 2007
Attribution: What is the cause of the detected climate
change?• Attribution is primarily model
based analysis• What mix of forcings is required to
create the detected climate change?
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2020Climate Change 101March 12, 2007
Attribution example: Most of the warming over the past 50 years is
likely due to greenhouse gas increases
IPCC TAR
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2121Climate Change 101March 12, 2007
Are CO2 and other greenhouse gasses really responsible for
changing the global temperature?
• Quantum physics says we should expect them to be
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2222Climate Change 101March 12, 2007
• Climate models say they are
Are CO2 and other greenhouse gasses really responsible for
changing the global temperature?
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2323Climate Change 101March 12, 2007
Are CO2 and other greenhouse gasses really responsible for
changing the global temperature?
• Historical observations indicate they are related
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2424Climate Change 101March 12, 2007
Are CO2 and other greenhouse gasses really responsible for
changing the global temperature?• Ice cores can give us the long view
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2525Climate Change 101March 12, 2007
Are CO2 and other greenhouse gasses really responsible for
changing the global temperature?• The long view says they are definitely related
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2626Climate Change 101March 12, 2007
Common questions
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2727Climate Change 101March 12, 2007
You can’t predict the weather 10 days in advance, how can you predict the
climate 100 years from now?• Weather forecasting
and climate projections are very different– Weather forecasting
is primarily based movements and interactions of weather parameters
• Predicting a storm 1 day late is an error
– Climate projections are primarily based on the physics of long-term changes in solar energy and infrared radiation
• The same climate physics that allow us to 100% accurately predict that next summer will be warmer than next winter
After Kiehl and Trenberth (1997)
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2828Climate Change 101March 12, 2007
Don’t urban heat islands – hot local temperatures caused 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 and shows warming
• Increasing temperatures supported by:– plant bloom dates– Lake/river
freeze/thaw dates– Glaciers melting– Etc.
Peterson and Owen (2005)
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2929Climate Change 101March 12, 2007
Additional supporting evidence: the shrinking Arctic
sea-ice
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3030Climate Change 101March 12, 2007
Don’t satellites show no warming?
• One satellite data set did several years ago
• As another group tried to reproduce it, an error in the data processing was discovered
• Both satellite and surface data currently show warming
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3131Climate Change 101March 12, 2007
What are the climate projections for my area?
• Models aren’t accurate at city level• But can use projections for a large
region such as the Eastern US• Projections are not from the
Intergovernmental 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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3232Climate Change 101March 12, 2007
Precipitation
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3333Climate Change 101March 12, 2007
Total precipitation:
From Peterson et al., 2007b
1σ = ~68%2σ = ~95%
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3434Climate Change 101March 12, 2007
Precipitation projections:
• Total precipitation very uncertain
• However, models project heavy precipitation will increase
Created for a report due to be released in late 2007.
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3535Climate Change 101March 12, 2007
Temperature
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3636Climate Change 101March 12, 2007
Low CO2 scenario
From Peterson et al., 2007b
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3737Climate Change 101March 12, 2007
Mid-range CO2 increases
From Peterson et al., 2007b
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3838Climate Change 101March 12, 2007
Business as usual CO2
From Peterson et al., 2007b
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3939Climate Change 101March 12, 2007
Temperature projections
• Projections show more change in the future than recently observed
• Even if we stopped emitting CO2 now there would still be warming for the next few decades
• How warm it will be 100 years from now is dependent on future emissions of greenhouse gases
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4040Climate Change 101March 12, 2007
Does anthropogenic global warming pass the rating
criteria?• Testability– Can it be proved false?
• Yes, the last decade could have been cold, laboratory tests on CO2 could have proven theory wrong
• Fruitfulness– Does it yield observable surprising predictions?
• Yes, predicts increase in heavy precipitation which has been observed
• 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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4141Climate Change 101March 12, 2007
Ockham’s razor• 14th Century English Franciscan friar and
philosopher William of Ockham developed this principle:– 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 CO2’s radiative effect– Paying attention to unproven explanations
» It is just part of a natural cycle (that doesn’t 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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4242Climate Change 101March 12, 2007
Final comment
• Stepping out into record hot weather, a friend who is an expert on climate change detection and attribution was asked if the high temperatures they were experiencing were due to global warming
• He responded:– You can’t attribute any one day’s
temperature to global warming– But unusually warm weather like that does
give us the privilege of experiencing the weather we are bequeathing our children and grandchildren
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4343Climate Change 101March 12, 2007
Selected References
• Kiehl, J., and K. Trenberth, 1997: Earth’s annual global mean 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 Vázquez Aguirre, 2007a: Changes in North American extremes derived from daily weather data. Proceedings of the National Academy of Science, in preparation.
• Peterson, Thomas C., Marjorie McGuirk, Tamara G. Houston, Andrew H. Horvitz and Michael F. Wehner, 2007b: Climate Variability and Change with Implications for Transportation, National Research Council, in press.
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4444Climate Change 101March 12, 2007