MET 112 Global Climate Change - Lecture 8Temperature GraphSlide 3Earth’s ClimateStability versus instabilityStates of equilibriumClimate StabilitySlide 8Climate FeedbacksPositive FeedbacksIce-Albedo Feedback (Cooling)Fill in the blanksIce-Albedo Feedback (Warming)Slide 14Water Vapor Feedback (Warming)Water Vapor Feedback (Cooling)Negative FeedbacksPossible Role of Cloud in Warming or Cooling the AtmosphereWhich feedback is positive?As a result of the earth’s warming over the last 100 years, plants have been growing at a faster rate. Because plants absorb CO2, the increase in plant growth means that more CO2 is being absorbed from the atmosphere by plants.MET 112 Global Climate Change - Lecture 8Climate FeedbacksDr. Craig ClementsSan Jose State UniversityTemperature GraphThe Earth’s climate is fairly stable in terms of temperatureThis can be visualized using in the following system diagram.The idea is that even though the system may change away from it’s initial point, it will have the tendency to go back to ‘normal’ eventually.Earth’s ClimateStableStable123Stability versus instabilityStable equilibrium Unstable equilibriumStable: –Given a perturbation, the system tends to return to original stateInstability: –Given a perturbation, the system moves to another state.–The system may have multiple states of equilibriumStates of equilibriumStable to small perturbations, until a big force perturbs the system into a new equilibrium213Climate StabilityThe Earth’s climate changes as a result of internal/external forcing:–Changes in solar radiation–Changes in the earth’s orbit–Plate tectonics–Volcanoes–Human pollution etc.These forcings can be thought of as a perturbation (or push) to climate stability.These changes can be enhanced or diminished by positive or negative feedbacks8 MET 112 Global Climate MET 112 Global Climate ChangeChangeClimate StabilityInternal Forcing mechanisms - processes that are internal to the climate system that involve the various elements: ice, water vapor, CO2External Forcing mechanisms- some forcing that can alter the system without itself being altered. - solar variability, axis wobble, etc.Climate FeedbacksPositive feedback: –initial change reinforced by another process.–Trends towards instabilityNegative feedback: –initial change counteracted by another process.–Trends towards stabilityPositive FeedbacksProcesses that accelerate a change–Note: Feedbacks cannot initiate change; they can only alter the pace of changeImportant climate examples:–Ice-albedo feedback–Water-vapor feedback–Cloud feedbackIce-Albedo Feedback (Cooling) Earth CoolsIce Coverage IncreasesAlbedo IncreasesAbsorption of Sunlight DecreasesInitiating MechanismSomehow this happensPositive FeedbackFill in the blanks Earth WarmsIce Coverage ___________ Albedo _____________Absorption of Sunlight _______ Initiating Mechanism1. increases, decreases, decreases2. Decreases, decreases, increases3. Increases, increases, increases4. Decreases, decreases, decreasesIce-Albedo Feedback (Warming) Earth WarmsIce Coverage DecreasesAlbedo DecreasesAbsorption of Sunlight IncreasesInitiating MechanismPositive FeedbackFill in the blanks1. Increases, increases, increases2. Increases, decreases, decreases3. Decreases, increases, increases4. Decreases, decreases, decreasesEarth Warms Evaporation Atmospheric Water Vapor Content Greenhouse Effect Initiating MechanismWater Vapor Feedback (Warming) Earth WarmsEvaporation IncreasesAtmospheric Water Vapor Content Increases Greenhouse Effect StrengthensInitiating MechanismPositive FeedbackWater Vapor Feedback (Cooling) Earth CoolsEvaporation DecreasesAtmospheric Water Vapor Content Decreases Greenhouse Effect WeakensInitiating MechanismPositive FeedbackNegative FeedbacksProcesses that reduces an imposed change - Trends towards stabilityImportant examples:–Cloud feedback–Chemical weatheringNote: Positive/negative feedbacks have no relation to ‘good versus bad’, but are about how a system responds to a change.Possible Role of Cloud in Warming or Cooling the AtmosphereFigure 12.7 Role of cloud in both warming and cooling the atmosphere.Increased warming bytrace gases(including water vapour)Increased airtemperaturesIncreased watervapourIncreased cloudamountof terrestrial radiationIncreased trappingIncreased reflectionof solar radiationWarmingCoolingNet warmingor coolingWhich feedback is positive?Figure 12.7 Role of cloud in both warming and cooling the atmosphere.Increased warming bytrace gases(including water vapour)Increased airtemperaturesIncreased watervapourIncreased cloudamountof terrestrial radiationIncreased trappingIncreased reflectionof solar radiationWarmingCoolingNet warmingor cooling1. Left2. RightAs a result of the earth’s warming over the last 100 years, plants have been growing at a faster rate. Because plants absorb CO2, the increase in plant growth means that more CO2 is being absorbed from the atmosphere by plants. 1. This is a positive feedback.2. This is a negative feedback.3. This has nothing to do with
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