Chapter 3: The Big Picture: Systems of Change

Systems A system is a set of components or parts that function together to act as a whole. –E.g. Body, city, river Open system- some energy or material moves into or out of system. Closed system- no such movements take place.

Feedback Feedback is when one part of the system changes –Those changes affect another part of the system –Which affects the first change Negative feedback- an increase in output leads to a later decrease. –Self-regulating, or stabilizing

Feedback Positive feedback- an increase in output leads to a further increase in the output. –Destabilizing Environmental damage can be especially serious when peoples use of the environment leads to positive feedback.

Positive Feedback

Feedback Some situations involve both + and – feedback. Human pop in large cities.

Stability A stable system is one that –Has a condition that it remains in unless disturbed. –Condition that it returns to if disturbed from it and the cause of the disturbance stops. Whether this is desirable depends on the system and potential changes.

Exponential Growth Growth occurring at a constant rate. –(rather than a constant amount) Plotted on a graph will form a J shaped curve

Exponential Growth Calculating EG involves two related factors –Rate of growth measured as a % –Doubling time in years Time necessary for the quantity being measured to double. EG is positive feedback and incompatible w/ sustainability

Environmental Unity It is impossible to change only one thing –Everything effects everything else Earth and its ecosystems are complex entities in which any action may have several or many effects.

Environmental Unity: An Urban Example Many midwestern US cities (i.e. Chicago) have had a shift in land use –Forest or ag land to urban development Construction increases runoff and soil erosion –Effects river channels and flood hazard After construction sediment load decreases but runoff still increases Thus land-use changes set off a series of changes which can trigger additional changes.

Environmental Unity: A Forest Example Forest, stream and fish in the Pacific Northwest Wood debris form and maintain pool environments in small stream. –Provide rearing habitat for young salmon –Formerly removed because thought to block fish migration Studying relations between physical and biological systems at the heart of enivor science

Uniformitarianism The physical and biological processes presently forming and modifying Earth are the same now as they were in the past. A study of past and present processes is key to the future.

Changes and Equilibrium in Systems Steady state –Input into a system equals output –No net change in the size of the reservoir –Dynamic equilibrium Because material entering and leaving the systems in equal amounts

Changes and Equilibrium in Systems When input is less than output –The size of reservoir declines When input is greater than output –The size of the reservoir increases

Changes and Equilibrium in Systems Average residence time- the time it takes for a given part of the total reservoir of a particular material to be cycled through the system. Large systems w/ a slow rate of transfer of water have a long residence time –Oceans –Difficult to clean up –Contrast to a stream w/ high rate of transfer

Earth and Life Earth formed 4.6 billion years ago Life began on Earth 3.5 billion years ago –Since life’s emergence many organisms have evolved, flourished, and become extinct. Humans to may some day become extinct. –Human activities increase and decrease the magnitude and frequency of natural processes. –Leading to many human caused extinctions.

Earth as a Living System Biota- all living things within a given area Biosphere- region of Earth where life exists –Also includes the system that sustains life All living things require energy and materials. –Energy from the sun and interior of Earth –Materials recycles through the system

Ecosystem A community of organisms and its local nonliving environment in which matter cycles and energy flows. Can be applied to different scales –Puddle to forest to planet –What is common to all is not physical structure but existence of processes –Can be natural or artificial

Gaia hypothesis The hypothesis states that life manipulates the environment for the maintenance of life. –Planet capable of physiological self-regulation Really a series of hypotheses –Life has greatly affected the planetary environment –Life has altered Earth’s enviro in ways that have allowed it to persist

Why Solving Environmental Problems Is Often Difficult 1. Exponential growth –The consequences of EG and its positive feedback can be dramatic, leading to incredible increases of what is being evaluated or measured.

Why Solving Environmental Problems Is Often Difficult 2. Lag time –The time between a stimulus and the response of a system. –Long lag time or delays may lead to overshot and collapse –Going beyond the carry capacity can lead to a collapse of a population.

Why Solving Environmental Problems Is Often Difficult 3. Irreversible consequences –Consequences that may not be easily rectified on a human scale of decades or a few hundred years.