An Introduction to Systems

The Climate System We will often refer to the “Climate System” Can you name the components of the climate system?

The Climate System Atmosphere Ocean Solid Earth (Lithosphere) Hydrosphere Cyrosphere Biosphere

Systems Approach Consider the earth climate system as a whole and consider the interactions between the components. How do the climate system components interact? Consider also internal and external forcings (natural and human-induced).

The Climate System

Examples of Forcings Increase in atmospheric greenhouse gas concentrations. (internal) Introduction of ozone destroying chemicals into stratosphere. (internal) Deforestation and loss of biodiversity. (internal) Changes in earth’s orbit. (external) Solar variations. (external) Asteroid and comet impacts. (external)

Hypothesis In order to understand the current earth climate and possible future climate changes, we must also consider the earth’s climate in the past. Past climate indicates the relative importance of the interactions between the components of the climate system, and the resilience of climate to perturbations, both natural and human-induced (anthropogenic).

How do we determine the changes that may result? We need a framework in which to view the climate system in a logical and quantitative way.

Overview Couplings Feedback loops Equilibrium states Perturbations and forcings An example – “Daisyworld”

Couplings and Feedback Loops By way of an illustrative example, consider the relationship between your body temperature and an electric blanket.

Control Response Control Response

Overall Feedback Effect Treat positive couplings as a “+” Treat negative couplings as a “-” Overall feedback = product of “+” and “-” Preceding example: + multiplied by - = “-”

Jimmy has Rosalynn’s blanket controller and vice versa.

Equilbrium States Feedback loops will lead to an “equilibrium state”. In the case of the electric blanket, the equilibrium state occurs when the temperature is just right! The equilibrium state will not change unless something is disturbed. For negative feedbacks, the equilibrium state is stable. There are unstable equilibrium states also, often due to positive feedbacks.

Stable and Unstable Equilibrium States

Perturbations and Forcings Volcanic influences on the global atmospheric temperature as an example. Volcanic eruptions release sulphate aerosol into the stratosphere. Sulphate aerosol reflects incoming solar radiation back to space – so earth cools. Eventually aerosol settles into the troposphere and is rained out and earth returns to equilibrium. A “stable” process i.e. there is a stable equilibrium.

The average effect on global average surface temperature due to volcanic eruptions

Stable and Unstable Equilibrium States

An illustrative example: Daisyworld A simple illustrative example proposed by James Lovelock of Gaia fame. The “Gaia hypothesis” basically states that earth is a self-regulating system in which biota play an integral role. Gaia – goddess of mother earth (Greek Myth). Illustrates that natural feedbacks can control the climate of a planet quite naturally without recourse to intelligent intervention (or design).

Albedo The primary controlling influence on Daisyworld is the surface “albedo.” Albedo=the fraction of incident solar radiation that is reflected back to space. Some examples from the climate system are …

Welcome to Daisyworld There are only two types of surface on Daisyworld: (1)Gray soil (2)White daisies

The feedback As daisy coverage increases, Albedo increases Net solar radiation absorbed at the surface decreases Surface temperature decreases What kind of coupling is this? “+” or “-”?

Control Response

ControlResponse

Daisyworld equilibria Daisy coverage also depends on surface temperature. If it is too hot or too cold, daisies will not survive – hence there are critical thresholds for daisies. There is an “optimum” temperature for daisy growth – a temperature which is “just right” for daisies (the “Goldilocks” effect).

Control Response

Equilbrium Climate We have two relationships: (i)Surface temp vs daisy coverage (i)Daisy coverage vs surface temp. Clearly they are not independent so we can combine them to determine the states of the system when they are both satisfied simultaneously. This occurs at the equilibrium points. ControlResponse Control

+ Surface temp vs daisy coverage Daisy coverage vs surface temp

Stability of the equilibrium climate “+” X “-”=“-” “-” X “-”=“+”

Daisyworld response to climate forcing What will be the response of Daisyworld to a steady increase in the solar luminosity? What will be the ultimate of fate of daisyworld?

For a given daisy coverage, temperature increases with increasing solar luminosity.

So what happens as solar luminosity continues to increase?

Change in daisy coverage versus solar luminosity. Once surface temp reaches the optimum value, all feedbacks are positive and all daisies rapidly perish. As solar luminosity increases, temp increases. However as daisies begin to grow the albedo reduces the surface temperature compared to the that if there were no daisies. Once the optimum temperature is reached, all feedbacks are positive and the daisies rapidly perish so temp continues to rise because the albedo is now lower. No daisies

Review of important ideas There are natural feedbacks in the climate system. Negative feedbacks lead to stable equilibria. Positive feedbacks lead to unstable equilibria. Feedbacks can very naturally control climate in a self-governing way.