An Introduction to Systems DaisyWorld An Introduction to Systems

Key Questions What are systems? What are feedback loops? What are equilibrium states? Does viewing Earth as a system allow for deeper insight into the interrelationships among the physical and biological worlds? Can Earth’s climate be self-regulating? Chapter focus – the fundamentals of systems theory needed to study Earth

Systems Approach Human physiology Systems interrelated, function together to maintain the body in a healthy state

System Essentials System – composed of diverse but interrelated components that function as a complex whole Components can be: reservoir of matter reservoir of energy system attribute subsystem Feedback Loops: How nature gets its rhythms

State of a System Set of important attributes that characterize the system at a particular time Components interact so that a change in state is sensed by the whole system This linkage allows for the control of important attributes

Couplings Links between systems that allow the flow of information from one component to the next Electric blanket example

Systems Diagrams Keep track of couplings within a system Positive Coupling – a change ( or ) in one component leads to a change in the same direction in the linked component - represented by  Negative Coupling - a change in one component leads to a change in the opposite direction in the linked component - represented by 

Feedback Loops Positive Feedback Loops – amplify the effects of the disturbance Negative Feedback Loops – diminish the effects of the disturbance “Sign” of the Loop – odd number of negative couplings – negative even number of negative or all positive couplings- positive Feedback is a self-perpetuating mechanism of change and response to that change

Equilibrium State Condition will not change unless the system is disturbed Stable Created by negative feedback loops Modest disturbances will be followed by return to equilibrium state Unstable Slight disturbance carry the system further and further away from the state

Stable State Small disturbances followed by return to equilibrium state Large disturbances can lead to a new different equilibrium state There are limits to the stability of stable equilibrium states

Unstable States Will not return to original state on its own No region of stability Will not return to original state on its own Slightest disturbance pushes system to a new stable equilibrium

Equilibrium State For natural systems with a single feedback loop it is usually true that Stable systems result from negative feedback loops Unstable systems result from positive feedback loops

Perturbations and Forcings Perturbation – temporary disturbance of a system Volcanic eruption example – average climatic response to the 5 largest eruptions in the last 100 years

Perturbations and Forcings Forcing – more persistent disturbance of a system Solar Luminosity example Increase in temperature countered by decrease in CO2 LLGHG = Long Lived Greenhouse Gases

Daisyworld Hypothetical planet with a simpler climate system Only life forms are daisies Creation of Lovelock & Watson DaisyWorld (1): James Lovelock and Gaia DaisyWorld (2): Gaia and Daisyworld DaisyWorld (3): Self regulation DaisyWorld (4): Gaia theory and the real world Demonstrates that natural systems can be self-regulating on a global scale without the need for intelligent intervention This World Is Black and White

Daisyworld Climate System A two component system Area of white daisy coverage Average surface temperature Daisy coverage affects temperature Temperature affects daisy coverage

Daisyworld Couplings Albedo – reflectivity of a surface Expressed as a decimal fraction of the total incoming energy reflected from the surface

Surface Temperature vs Daisy Coverage Negative Coupling Negative slope Daisy Coverage - Surface Temp 

Coupling: Daisy Coverage – Albedo - Temperature

Daisy Coverage in Response to Temperature

Equilibrium States Put the two together Intersection shows Effect of daisies on temperature AND Effect of temp on daisies EQUILIBRIUM STATES Two Feedback loops One above optimum One below

Feedback Loops

THE DAISY WORLD CLIMATE SYTEM Response of Daisy world to perturbations depends on the temperature Below optimum has negative feedback loop and is stable Above optimum has positive feedback loop and is unstable

Response to External Forcing Increased solar luminosity Daisies would increase (immediately) and albedo increase and warming would be slowed Persistent increasing solar luminosity would eventually lead to a new higher equilibrium temperature, but it would happen at a much slower rate (daisies & environment feedback loops)

More Accurate Response to External Forcing Assumption – daisies respond to temperature change only So – no change to 

However, change in surface temperature and daisy coverage expected Temperature will be higher for any amount of daisy coverage So – change to 

Combine the two Graphs P1' stable P2' unstable Both temperature and daisy coverage higher at new stable equilibrium Stability limit for P1' is lower New equilibrium state less resistant to perturbations

Mathematically Speaking . . . Comparing equilibrium temperature with and without feedback ∆Teq = ∆T0 + ∆Tf The overall temperature change resulting from increase solar luminosity is the sum of the temperature change with no feedback and the temperature change due to feedback

For Any Stable Equilibrium in a System Involving Feedback Loops The change in state of a system as it moves from one equilibrium to the next is the sum of the state change that would result without feedback and the effect of the feedback itself To qualify the strength of the feedback effect . . .

The Feedback Factor The ratio of the equilibrium response to forcing (the response with feedback) to the response without feedback  = temperature change with feedback = ∆Teq temperature change w/out feedback ∆T0 Negative feedback loop if 0 <  < 1 Positive feedback loop if 1 <  Feedback factor defined only for stable systems

Daisyworld Climate History History of Daisy Coverage Temperature History -Initially temp rises quickly Once min temp for daisies met, daisies increase Growth of daisies cools planet Eventually, when optimal temp is met, daisy coverage at max Increasing solar luminosity not countered by daisy growth and daisies die, causing increasing temp Feedback loop positive & unstable Surface temp rises, daisies extinct

The Lessons of Daisyworld A planetary climate system is not passive in the face of internal or external forces Negative feedback loops counter external forcings Non-human systems that self-regulate seem intelligent, yet no foresight or planning is involved In a natural self-regulating system, there is no preset state that the system is programmed to “seek-out” Thresholds often exist in systems that when surpassed can lead to rapid changes in system state Abrupt changes can have no forewarning Earth is like Daisyworld Strong negative feedback loops lead to long-term stability Are we approaching a climate threshold that will result in a much warmer state?