CLIM 101 Weather Climate and Global Society Understanding
CLIM 101: Weather, Climate and Global Society Understanding uncertainties and feedbacks Jagadish Shukla Lecture 15: 22 Oct, 2009
Reading for Week 8 Lecture 15 Understanding uncertainties and feedbacks • GW Chapter 3, 5
CLIM 101: Weather, Climate and Global Society Uncertainty and Feedback
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
observations in each 1° grid box at 250 m depth
URBAN HEAT ISLAND EFFECT full US Historical Climatology Network (USHCN) data USHCN data without the 16% of the stations with populations of over 30, 000 within 6 km in the year 2000 • UHI and changes in land use can be important for DTR at the regional scale Full USHCN set minus the set without the urban stations • The global land warming trend is unlikely to be influenced significantly by increasing urbanization. USHCN data for the 16% of the stations with populations over 30, 000
¬------- Little change ---- Variability due to solar changes, volcanism ¬ Cooling Increased post. WWII pollution in NH ¬ Warming Increasing GHG
Slope = 1. 02 Slope = 1. 67 Slope = 1. 01 Slope = 1. 82 Synthetic time series example: Need large samples to avoid “end effects” in estimating linear trends
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)
The IPCC AR 4
Climate models without volcanic Forcing OHC - ocean heat content Th. SL: Thermosteric sea level change (density changes induced by temperature change) Domingues et al. 2008
Climate models with volcanic Forcing (0 -700 m) Th. SL: Thermosteric sea level change (density changes induced by temperature change) Domingues et al. 2008
Global mean sea level (deviation from the 1980 -1999 mean) Uncertainty in estimated long-term rate of sea-level change Based on tide gauges Based on satellite altimetry Range of model projections (SRES A 1 B scenario)
Clouds: Still the Largest Source of Uncertainty
Climate Model Fidelity and Projections of Climate Change J. Shukla, T. Del. Sole, M. Fennessy, J. Kinter and D. Paolino Geophys. Research Letters, 33, doi 10. 1029/2005 GL 025579, 2006 Center of Ocean-Land. Atmosphere studies
Increase in Surface Temperature Observations Predictions with Anthropogenic/Natural forcings Predictions with Natrual forcings 1. 0º C IPCC 2007
Projected Future Warming Figure 9. 13, IPCC TAR
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. CO 2 Eq 3. 4 o. C = 6. 1 o. F 850 2. 8 o. C = 5. 0 o. F 600 1. 8 o. C = 3. 2 o. F 0. 6 o. C = 1. 0 o. F 400
CLIM 101: Weather, Climate and Global Society Uncertainty
CLIM 101: Weather, Climate and Global Society Feedback
Positive vs. Negative Feedback 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
Effect of Positive Feedback (1) Temperature With positive feedbacks If no feedbacks present Time
Effect of Positive Feedback (2) Temperature If no feedbacks present With positive feedbacks Time
The Need for Negative Feedbacks • Positive feedbacks are destabilizing - they tend to drive the system away from equilibrium • Negative feedbacks are required to restore equilibrium
A System Without Negative Feedbacks Temperature Example “Runaway Greenhouse Effect”, T H 2 O T Catastrophic Warming! Time
Temperature The Way Physical Systems Usually Behave Warming Accelerating Warming Decelerating Time
Feedbacks - Summary • Positive feedbacks tend to increase the amplitude of the system response • Negative feedbacks tend to reduce the amplitude of the system response
Feedbacks in the Biosphere 1. The plankton multiplier in the ocean (positive) (Colder Stronger Ocean Biological Pump Remove ATM CO 2) 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 permafrost (positive)
Feedbacks in the Climate System 1. Water vapor feedback 2. Cloud-radiation feedback 3. Ice-albedo feedback 4. Climate-Carbon Cycle feedback
Ice-Albedo Feedback (1) Cooling Ice Increases Albedo Increases Absorption of sunlight decreases
Ice-Albedo Feedback (2) Warming Ice Decreases Albedo Decreases Absorption of sunlight increases
Water Vapor Feedback (1) Warming Evaporation from the Oceans Increases Atmospheric Water Vapor Increases Stronger Greenhouse Effect
Water Vapor Feedback (2) Cooling Evaporation from the Oceans Decreases Atmospheric Water Vapor Decreases Weaker Greenhouse Effect Water Vapor Feedback is Positive
Understanding and Attributing Climate Change 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? Center of Ocean-Land. Atmosphere studies
Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR) Definition: The ECS is the full equilibrium surface temperature response to a doubling of CO 2 Definition: The TCR is the surface temperature response at CO 2 doubling for a 1%/yr increase of CO 2 (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: Center of Ocean-Land. Atmosphere studies
Climate Model Fidelity and Projections of Climate Change J. Shukla, T. Del. Sole, M. Fennessy, J. Kinter and D. Paolino Geophys. Research Letters, 33, doi 10. 1029/2005 GL 025579, 2006 Center of Ocean-Land. Atmosphere studies
THANK YOU! ANY QUESTIONS? Center of Ocean-Land. Atmosphere studies
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