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EESA01H3 (137)
Lecture

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School
University of Toronto Scarborough
Department
Environmental Science
Course
EESA01H3
Professor
Carl Mitchell
Semester
Fall

Description
Earths Environmental Systems y Our planets environment consists of complex networks of interlinked systems y Earth uses cycles that shape the landscapes around us and guide the flow of key chemical elements and compounds that support life and regulate climateSystems show several defining properties y System is a network of relationships among parts elements or components that interact with and influence one another through the exchange of energy matter or information y Open Systems are systems that receive input of both energy and matter and produce outputs of both y Closed Systems receive inputs and produce outputs of energy but not matter o in nature no system is perfectly closed y Energy inputs to the earths environmental systems include o Solar radiation o Heat released by geothermal activity o Organismal metabolism o Human activities eg Fossil fuel combustion y Information energy can come in the form of sensory cues from o visual signs o Olfactory chemical signs o Magnetic signs o Thermal signs CyrosphereArtic GlacierInputs of matter occur when chemicals or phyrical material among systemsSeeds dispered long distances y Inputs of matter occur when chemicals or physical material moves among systems o Eg Seeds being dispered long distances o Migratory animals deposit waste far from where they consumed food y Eg Gulf of St Lawrence receives inputs from the St Lawrence fishers harvest some of the systems output matter and energy in the form of fish and plankton o Output becomes input to the human economic system and to the digestive systems of the people who consumer seafood from the St Lawrence y Sometimes a systems output can serve as input to that same system o This is a circular process known as feedback loopCan be positive or negative y In a negative feedback loop output that results from a system moving in one direction acts as input that moves the system in the other directiono Input and output essentially neutralize each other o EG Thermostat working to stabilize rooms temperature o EG Our bodies when we get too hot our sweat glands pumpe out moisture that evaporates to cool us downMost systems in nature involve negative feedback loops y Positive feedback loops have the opposite effect rather than stabilizing a system they drive it further toward one extreme or another o eg Populations growth the more people who are born the more there are to give birth to further people increased output leads to increased input leading to further increased output o Positive feedback loops are rare in nature common in natural systems altered by human impact y System is constantly active as input and outputs occur simultaneously y When processes within a system move in opposite directions at equivalent rates so that their effects balance out is called dynamic equilibrium o Dynamic because even though the state is balance it is everchanging o Homeostasis is the tendency of a system to maintain constant or stable internal conditionsHomeostatic systems are often said to be in a stable or steady stateEarth is a homeostatic system o Resistance refers to the strength of a systems tendency to remain constant o Resilience is a measure of how readily the system will return to its original state once its been disturbedy It is difficult to understand systems fully by focusing on their individual components because systems can show emergent properties o Characteristics not evident in the components alone o It is like saying the whole is more than the sum of its partsIf you had a tree in its components parts leaves branches you wouldnt be able to predict the whole trees emergent properties which include the role the tree plays as a habitat for birds etc You could analyze the trees chloroplasts but still be unable to understand the tree as habitat y Systems have well defined boundaries o Computerdesktop example y In summary systems may exchange energy matter and info with other systems which may contain or be contained within other systems where we draw boundaries may depend on the spatial or temporal scale at which we choose to focus Understanding a complex system requires considering multiple subsystems y The great lakes st Lawrence riveratlantic ocean are systems that interact with one another
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