UAU102F, University of Iceland

Transcription

1 Systems, systems theory, thermodynamics SYSTEMS System A set of components that interact with one another A system must be distinguishable from its environment (i.e. must be able to identify it) Systems analysis Concerned with the nature of interactions as well as the components Interested in patterns, behaviors Introduction to Environmental Science and Natural Resources ThrosturTh@hi.is SYSTEMS Isolated System No matter (energy or materials) in or out of the system Example? Closed System No material movement into or out of the system Example? Open System Energy or material moves into or out of the system Example? SYSTEMS Plants as open systems Exchange energy and matter with environment Highly ordered system, takes from environment to maintain order (life). Death: deacay and disorder begins Autotrophs (producers), make organic matter from inorganic matter using energy via photosynthesis Primary productivity: rate at which plants produce plant tissue GPP: Total amount of solar energy fixed by photosynthesis NPP: GPP maintenance respiration PHOTOSYNTHESIS ENVIRONMENTAL UNITY Environmental unity: It is impossible to change only one thing; everything affects everything else. Example: a food web Holistic perspective needed (ThrosturTh@hi.is) 1

2 UNIFORMITARIANISM Uniformitarianism suggests studying the past and the present is the key to the future. The present is the key to the past. Implications? CHANGES AND EQUILIBRIUM IN SYSTEMS Stocks and flows t u 0 Steady/Stable state A dynamic equilibrium Material or energy is entering and leaving the system in equal amounts Opposing processes occur at equal rates E.g. climax state in mature ecosystems What goes in System no change Comes out SYSTEMS FEATURES Have components State variables stocks Sources, sinks Interactions flows Energy, materials, information Static behavior Dynamic behavior Interactions Relational Physical SIMPLE SYSTEM S I O Average residence time S T F 3 Reservoir size(e.g. m ) 3 m Flux (e.g. ) s 2005 John Wiley and Sons Publishers CHANGES AND EQUILIBRIUM IN SYSTEMS Relationships between variables e.g. cause (inflow) and effect (outflow) Feedback Growth Linear Nonlinear Wonderfully complex! Relationship Deterministic Stochastic Continuous Discrete Thresholds Delayed (lags) DYNAMIC BEHAVIOR: FEEDBACK Feedback Occurs when the output of the system also serves as an input, leading to further changes in the system Negative Feedback Occurs when the system s response is in the opposite direction of the output Self-regulating Stabilizing Positive Feedback Occurs when an increase in output leads to a further increase in output Destabilizing (ThrosturTh@hi.is) 2

3 ILLUSTRATED USING CAUSAL LOOP DIAGRAMS HERE CLIMATE CHANGE DYNAMIC BEHAVIOR: GROWTH Linear growth N N 0 r t Exponential growth: Growth occurs at a constant rate per time period Exemplifies positive feedback Equation to describe exponential growth is: N N0 exp( k t) Destabilizing 2005 John Wiley and Sons Publishers POPULATION GROWTH Exponential growth Characterizes anything that can grow without limit N N0 exp( k t) Absolute increaseincreases over time Linear Cubic (non-linear) Exponential DOUBLING TIME dn r: growth rate r N dt N N exp( r ) 0 t Doubling time N 2N0 N0 exp( r t2x) Take natural log at both sides t ln(2) x r r or 70/(growth rate in %) DENSITY DEPENDENT GROWTH S-shaped growth curves Carrying capacity, determined by e.g.: Available resources Technology Growth rate r LOGISTIC OR DENSITY DEPENDENT GROWTH Upper limit to the ultimate size Determined by carrying capacity, K What defines K? Growth determined by: K N K N0 1 exp( r t) N 0 (ThrosturTh@hi.is) 3

4 LOGISTIC GROWTH CURVE Growth curve u-shaped dn N r N 1 dt K DYNAMIC BEHAVIOR: RELATIONSHIPS BETWEEN VARIABLES Deterministic Stochastic Continuous Discrete Thresholds Delayed (lags) Stabilizing DYNAMIC BEHAVIOR Thresholds A tipping point Lags Separation between cause and effect in: Time Space Results in oscillations PUTTING IT ALL TOGETHER Negative loops with delayed feedback Impact of overshoot not immediately realized. Creates oscillations. Coupled negative and positive feedback loops E.g. logistic growth. Interaction between e.g. species interacting movements Predator - prey Symbiosis EQUILIBRIUM AND STABILITY RESILIENCY Equilibrium More than one? Will the variable remain at this level? Stability Will the variable return to equilibrium after a shock? Resilience Returns to equilibrium Maintains functional integrity Maintains functional integrity when faced with a disturbance Stability Biodiversity Keystone species Adaptation Fundamental concept with regard to climate change adaptation When are societies sufficiently resilient to cope? (ThrosturTh@hi.is) 4

5 WHY SOLVING ENVIRONMENTAL PROBLEMS IS OFTEN DIFFICULT 1. Feedback loops - coupled or single 2. Exponential growth The consequences of exponential growth and its accompanying positive feedback can be dramatic 3. Lag time The time between a stimulus and the response of a system If there is a long delay between stimulus and response, then the resulting changes are much more difficult to recognize. 4. Irreversible consequences Consequences that may not be easily rectified on a human scale of decades or a few hundred years. When are activities irreversible? WHY SOLVING ENVIRONMENTAL PROBLEMS IS OFTEN DIFFICULT 5. Everything is interlinked Makes it difficult to manage one species at a time 6. Synergy Pollutants often interact to create something worse 7. Never static - always changing, always dynamic E.g. succession - never constant. 8. Chaos Chaotic behavior very common - difficult to predict movement THERMODYNAMICS Study of energy transformations. Movement of matter (energy and materials) Fundamental to understanding environmental and economic systems Energy: the potential to do work or supply heat Work: when something is moved Power: work per unit of time Entropy: Level of disorder, chaos THERMODYNAMICS First law: Law of Conservation of Matter, matter can neither be created nor destroyed, only converted Implications, In = Out Materials balance principle Deals with quantity Open, closed and isolated systems THERMODYNAMICS Second law: Entropy Law Quality based no free lunch! Conversions means losses, increase in entropy or disorder in an isolated system Implications for an isolated system? Never reaches 100% efficiency Require energy for all transformations and thus maintaining order requires energy Diminishing return to technological change (ThrosturTh@hi.is) 5

6 BEST FIRST PRINCIPLE Extract best resources first Best: Most concentrated Least entropy Most distinguishable from the surrounding environment Require least energy to extract E.g. iron ore, copper ENERGY RETURN ON INVESTMENT: EROI Total amount of energy required for a process compared to energy out. Energy out/energy in System boundaries important Indicates e.g.: Efficiency of processes Scarcity or resources EROI Quantity of energy supplied EROI Quantity of energy used in supply process MEASUREMENT AND UNCERTAINTY Uncertainty: Sources Nature is variable Measurement uncertainty Systematic errors Accuracy and Precision OBSERVATIONS, FACTS, INFERENCES, HYPOTHESIS Observation Inference Fact Hypothesis: When an inference is tested If then statements Dependent, independent variables Quantitative and qualitative data THE SYSTEMS (ThrosturTh@hi.is) 6

7 4 MAIN SYSTEMS 1. Lithosphere 2. Hydrosphere 3. Atmosphere 4. Biosphere Constant interactions between them! Human impact focus of environmental science THE LITHOSPHERE Consists of the upper part of the mantle and the crust Crust, less than 1% of the earth s mass Thickness varies from 5-35 km. Made from rocks, 2000 minerals - 8 elements account for 99% of mass Oxygen 47% Silicon 28% Aluminum 8% Iron 5% THE LITHOSPHERE THE HYDROSPHERE Igneous rocks (granite) Solidification of molten materials Sedimentary rocks (sandstone, limestone) Erosion, dissolved material, biological activity Metamorphic rocks (marble from limestone) Alteration of parent rock Constantly changing, but over long time-scales Granite Limestone Marble Basalt Sandstone Includes all water on Earth. Lakes, rivers, ocean, water vapor in the atmosphere 70 % covered with water; 97% in oceans, 2% in glaciers ice caps, 0,0001 vapor, 0,009 in rivers etc. Hydrological cycle Precipitation, evaporation Changes occur much faster than in lithosphere BUT Residence time varies, depending on the reservoir THE ATMOSPHERE THE BIOSPHERE 3 main layers Troposphere (weather), stratosphere, mesosphere Mostly composed of Nitrogen 78% Oxygen 21% CO2 0.04% Methane % More rapid timescales of change, residence time 10 yrs methane 100 yrs CO2 The biosphere is the life zone of the Earth and includes all living organisms, including man, and all organic matter that has not yet decomposed. Extends from top of troposphere to 10km below sea level Supports life Water, usable energy, air, suitable temperature, essential nutrients, trace elements (ThrosturTh@hi.is) 7

8 EARTH AS A LIVING SYSTEM (ThrosturTh@hi.is) 8