understanding uncertainties and feedbacks jagadish shukla clim 101: weather, climate and global...
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Understanding uncertainties and feedbacks
Jagadish ShuklaJagadish Shukla
CLIM 101: Weather, Climate and Global Society
Lecture 15: 22 Oct, 2009
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Reading for Week 8Reading for Week 8Lecture 15Lecture 15
Understanding uncertainties and feedbacks
• GW Chapter 3, 5
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CLIM 101: Weather, Climate and Global Society
Uncertainty Uncertainty and Feedbackand Feedback
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Sources of Uncertainty: Observations
• Instrument error
• Sparse, infrequent measurements - inadequate sampling or sampling bias
• Observing system change over time
• Mixing direct measurements and proxy measurements
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observations in each 1° grid box at 250 m depth
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full US Historical Climatology Network (USHCN) data
USHCN data for the 16% of the stations with populations over 30,000
USHCN data without the 16% of the stations with populations of over 30,000 within 6 km in the year 2000
Full USHCN set minus the set without the urban stations
• UHI and changes in land use can be important for DTR at the regional scale
• The global land warming trend is unlikely to be influenced significantly by increasing urbanization.
URBAN HEAT ISLAND EFFECT
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------- Little change ----Variability due to solar
changes, volcanism
Cooling Increased post-WWII pollution
in NH
Warming Increasing GHG
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Slope = 1.01Slope = 1.82
Slope = 1.02Slope = 1.67
Synthetic time series example: Need large samples to avoid “end effects” in estimating linear trends
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Sources of Uncertainty: Models
• Input data (forcing) uncertainty• Differing assumptions with respect to
relevant processes• Differing estimates of model parameters• Intrinsic unpredictability • Unpredictability of external phenomena
(e.g. volcanoes)
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The IPCC AR4
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Climate models without volcanic ForcingClimate models without volcanic Forcing
Domingues et al. 2008
ThSL: Thermosteric sea level change(density changes induced by temperature change)
OHC - ocean heat content
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Climate models withClimate models with volcanic Forcingvolcanic Forcing(0-700 m)
Domingues et al. 2008
ThSL: Thermosteric sea level change(density changes induced by temperature change)
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Global mean sea level (deviation from the 1980-1999 mean)
Uncertainty in estimated long-term rate of sea-level change
Based on tide gaugesBased on satellite altimetry
Range of model projections (SRES A1B scenario)
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Clouds: Still the Largest Source of Uncertainty
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Center of Ocean-Land-Atmosphere studies
J. Shukla, T. DelSole, M. Fennessy, J. Kinter and D. PaolinoGeophys. Research Letters, 33, doi10.1029/2005GL025579, 2006
Climate Model Fidelity and Projections of Climate ChangeClimate Model Fidelity and Projections of Climate Change
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IPCC 2007
1.0º C1.0º C
Increase in Surface TemperatureIncrease in Surface Temperature
ObservationsPredictions with Anthropogenic/Natural forcingsPredictions with Natrual forcings
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Projected Future Warming Projected Future Warming
Figure 9.13, IPCC TAR
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What is in store for the future and what has already been committed
Global warming will increase if GHGs concentration increase. Even if GHGs were kept constant at current levels, there is a “commitment” of 0.6°C of additional warming by 2100.
1.8oC = 3.2oF
2.8oC = 5.0oF
3.4oC = 6.1oF
CO2 Eq
850
600
4000.6oC = 1.0oF
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CLIM 101: Weather, Climate and Global Society
Uncertainty Uncertainty
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CLIM 101: Weather, Climate and Global Society
FeedbackFeedback
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Positive vs. Negative Positive vs. Negative FeedbackFeedback
1. Something triggers a small system change
2. The system responds to the change
3. Feedback
• Positive Feedback: The response accelerates the original change
• Negative Feedback: The response damps the original change
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Time
Tem
per
atu
re
If no feedbacks present
With positive feedbacks
Effect of Positive Effect of Positive Feedback (1)Feedback (1)
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Effect of Positive Feedback Effect of Positive Feedback (2)(2)
Time
Tem
per
atu
re
If no feedbacks present
With positive feedbacks
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The Need for Negative The Need for Negative FeedbacksFeedbacks
• Positive feedbacks are destabilizing - they tend to drive the system away from equilibrium
• Negative feedbacks are required to restore equilibrium
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A System Without Negative A System Without Negative FeedbacksFeedbacks
Time
Tem
per
atu
re
Catastrophic Warming!
Example “Runaway Greenhouse Effect”, T H2O T
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The Way Physical Systems Usually BehaveThe Way Physical Systems Usually Behave
Time
Tem
per
atu
re Warming Accelerating
Warming Decelerating
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Feedbacks - SummaryFeedbacks - Summary
• Positive feedbacks tend to increase the amplitude of the system response
• Negative feedbacks tend to reduce the amplitude of the system response
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Feedbacks in the Feedbacks in the BiosphereBiosphere
1. The plankton multiplier in the ocean (positive)
(Colder Stronger Ocean Biological Pump Remove ATM CO2)
2. Carbon dioxide fertilization, plant growth (negative)
3. Effect of higher temperatures on respiration (positive)
4. Reduction of forest growth because of climate change (positive)
5. Increased greenhouse gases due to increase of fires (positive)
6. Release of methane from wetland and permafrost (positive)
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Feedbacks in the Climate Feedbacks in the Climate SystemSystem
1.Water vapor feedback
2.Cloud-radiation feedback
3.Ice-albedo feedback
4.Climate-Carbon Cycle feedback
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Ice-Albedo Feedback Ice-Albedo Feedback (1)(1)
Cooling
Albedo Increases
Absorption of sunlight
decreases
Ice Increases
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Ice-Albedo Feedback Ice-Albedo Feedback (2)(2)
Warming
Albedo Decreases
Absorption of sunlight
increases
Ice Decreases
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Water Vapor Feedback Water Vapor Feedback (1)(1)
Warming
Evaporation from the Oceans Increases
Atmospheric Water Vapor Increases
Stronger Greenhouse Effect
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Water Vapor Feedback Water Vapor Feedback (2)(2)Cooling
Evaporation from the Oceans Decreases
Atmospheric Water Vapor Decreases
Weaker Greenhouse Effect
Water Vapor Feedback is Positive
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1. Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR)
• Definitions
• Model ECS and TCR—the role of feedbacks
2. Detection and Attribution
• Detection and Attribution of What?
• Modeling with and without anthropogenic forcing
3. Understanding?
Understanding and Attributing Climate ChangeUnderstanding and Attributing Climate Change
Center of Ocean-Land-Atmosphere studies
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Definition: The ECS is the full equilibrium surface temperature response to a doubling of CO2
Definition: The TCR is the surface temperature response at CO2 doubling for a 1%/yr increase of CO2 (i.e. at year 70)
a. ECS and TCR are basically model concepts
b. TCR < ECS
c. ECS is a measure of the feedbacks in the system:
Recall:
Equilibrium Climate Sensitivity (ECS) and Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR)Transient Climate Response (TCR)
Center of Ocean-Land-Atmosphere studies
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Center of Ocean-Land-Atmosphere studies
J. Shukla, T. DelSole, M. Fennessy, J. Kinter and D. PaolinoGeophys. Research Letters, 33, doi10.1029/2005GL025579, 2006
Climate Model Fidelity and Projections of Climate ChangeClimate Model Fidelity and Projections of Climate Change
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THANK YOU!
ANY QUESTIONS?
Center of Ocean-Land-Atmosphere studies