Lecture 9: SystemsQuestions on ozone, ozone “debate”?Start on systems & feedbacks.• System basics• Earth surface temperature as an indicator of climate change• System diagrams: couplings, feedback loopsFollowing Chapter 2 of textbook.For more info on misinfo…Prof. Paul R. Ehrlich and Prof. Anne H. Ehrlich (1998)Betrayal of Science and Reason:How Anti-Environmental Rhetoric Threatens Our Future.Island Press, Washington DCBy two respected Stanford University professors:Scholarly correction to misinformation printed in books/newpapapers about biodiversity loss, global warming,ozone depletion, etc.System essentials - 1system: “an entity composed of diverse but interrelated parts that function as a complex whole” (p. 18, Kump)examples: human body, nation, ecosystem, planet, computer, internet, car, traffic Characteristics of systems: - multiple components - components are somehow coupled to each other - energy and/or matter flows throughSystem essentials - 2Critical to understanding almost any system is to understandhow it handles (or processes) the energy and/or matter flowingthrough it.at equilibriumexamples:planet/temperature (F is flow of energy)body/weight (F is flow of food and water)FIN = FOUTwhere F = flow or fluxEarth as a coupled systemFig 1-1, KumpSystem essentials - 3component: any individual part of a system that can be conceptuallyseparated and described in terms of its state, its behavior,and its influence on other componentsQuite arbitrary; choice based on what makes sense – whathelps us diagnose and understand the system examples for a planet system: atmosphere, surface, biosphereState of a system: the set of important attributes that characterize the system at a particular time (p. 19) note: we can also speak of the state of a component examples: atmosphere: CO2 content surface: temperature biosphere: number of daisiesExample state of the system:GAAST1880 2000Observed changes in the Earth's Global Annual AverageSurface Temperature (GAAST) over the past 120 yearsGAASTThe main evidence that global warming is really happening isthat the earth’s surface temperature has increased over thepast century. What is meant by the phrase “the earth’ssurface temperature”? That is, how is this quantity defined andhow is it measured? Key point: global-average and annual-average Why is this quantity used as an indicator of climate change? (scientific reasons, practical reasons) Key points: - indicates a property of the entire planet (e.g. responds toplanetary energy balance) - living things are very sensitive to temperature - people and most life is at the surface - determined very accurately because random errors cancel out with millions of measurementsGAAST -2Average surface temperature is the best SINGLE indicator we have of the state of the Earth’s climate. But the earth’s “climate” is much much more than the average surface temperature! Describe two ways that the “climate” could change WITHOUT changing the global-annual-average surface temperature.- northern hemisphere cools; southern hemisphere warms- nighttime gets warmer; daytime gets cooler - changes in precipitation, wind (hurricanes), sea level, etc.Change in GAAST1880 2000Natural or Anthropogenic?How would we know?Variations of the Earth’s surface temperaturefor the past 1,000 yearsT-variations 1000-2000System Essentials - 4coupling: how one component affects another – how the stateor behavior of one component influences the state or behavior of another componente.g.: ocean temperature -> evaporation -> coastal rainfall electricblankettemperaturebodytemperaturepositive couplingABPositive coupling: if A goes up this causes B to go upelectricblankettemperaturebodytemperaturenegative couplingABNegative coupling: if B goes up this causes A to go downSystem Diagram - 1System diagram: allows us to keep track of the variouscouplings within a system” electricblankettemperaturebodytemperaturenegative feedback loopABNegative feedback loop is STABLE Stable: tends to return to equilibrium when perturbed Equilibrium: steady state; temperatures are “just right”System Diagram -2Jimmy’sbodytemperatureJimmy’sblankettemperatureRosalynn’sblankettemperatureRosalynn’sbodytemperatureFeedback loop:• count up the number of negative couplings• odd means "negative"• even or zero means "positive"Text Fig. 2-2The wild and crazy bedroom of former President Jimmy CarterEquilibrium states“A state of a system in which forces, influences, reactions,etc balance each other out so that there is no net change”Static equilibrium: couplings are inactive; system is at restDynamic equilibrium: couplings are active but are in balanceThermal equilibrium: no net heat exchangeChemical equilibrium: reaction and its reverse proceed at equal ratesMechanical equilibrium: not moving, forces balanced such that position is fixed example: ball-on-curved-surface (Fig 2-3)Stable equilibrium:Unstable equilibrium:position or state is restored after small perturbationsmall perturbation causes change of position or stateWelcome to Daisyworld!Themes:• Energy balance• Planetary albedo• Self-regulation• Graphs of two
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