Unit+1+-+Systems+and+models


 * Objectives **** : **

// 1.1.1 //// Outline the concept and characteristics of systems. //

The title of this course can be divided into three parts – ‘environment’, ‘systems’ and ‘societies’. Each part can be considered separately or **holistically** (i.e. together). This topic examines the systems approach to the course.

A system is an assemblage of parts and relationships between them, which together constitute an entity or a whole. The interdependent components are connected through the transfer of energy and matter, with all parts linked together and affecting each other. Examples of systems, with increasing levels of complexity, include particles, atoms, molecules, cells, organs, organ systems, communities, ecosystems, biomes, the Earth, the Solar System, galaxies and the universe.

The Systems approach, central to the ESS course, emphasises similarities in the ways in which matter, energy and information link together in a variety of different disciplines such as ecology, economics, geography and politics. This approach, therefore, allows different subjects to be looked at in the same way, and for links to be made between them. Although the individual parts of complex systems can be looked at independently, as is often the case in scientific investigations (the reductionist approach), this overlooks the way in which these systems operate as a whole – a holistic approach is necessary to fully understand the way in which they operate together.

Systems consist of: // 1.1.2 //// Apply the systems concept at a range of scales i.e., small scale local ecosystem, a large ecosystem such as tropical rainforest and a global ecosystem such as Gaia. //
 * Storages (of matter or energy)
 * Flows (inputs into the system, outputs from the system)
 * Processes (which transfer or transform energy or matter)
 * Feedback mechanisms that maintain stability and equilibrium.

// 1.1.3 //// Define the terms open system, closed system and isolated system. //

A system has **boundaries** or edges. In the case of an ecosystem, this might be for example, the low tide line on an island, the edge of a pond, or the edges of a hectare of grassland. Outside these boundaries is its **environment** i.e. what lies outside the system under study, but which influences, and is perhaps influenced by the system.

Systems can be divided into three types, depending on the flow of energy and matter between the system and the surrounding environment.

Both matter and energy are exchanged across the boundaries of the system (figure a). Open systems are organic (i.e. living) and so must interact with their environment to take in energy and new matter, and to remove wastes (e.g. an ecosystem). People are also open systems in that they must interact with their environment in order to take in food, water and obtain shelter, and produce waste products.
 * Open Systems **

A model of an ecosystem as an open, thermodynamic, non-equilibrium system is shown below. The external environment must be considered as an integral part of the ecosystem concept.



Energy but not matter is exchanged across the boundaries of the system (figure b). Examples are atoms and molecules, and mechanical systems. The Earth can be seen as a closed system: input = solar radiation (Sun’s energy or light), output = heat energy. Matter is recycled within the system. Although space ships and meteorites can be seen as moving a small amount of matter in and out of the Earth system, they are generally discounted. Strictly, closed systems so not occur naturally on Earth, but all the global cycles of matter (e.g. the water and nitrogen cycles) approximate to closed systems.
 * Closed Systems **

Neither energy nor matter is exchanged across the boundary of the system (figure c). These systems do not exist naturally, although it is possible to think of the entire universe as an isolated system.
 * Isolated Systems **


 * All natural systems are open systems where inputs and outputs are freely exchanged with other systems. **

Ecologists have identified a number of ecosystems at different scales which have a distinctive pattern of relationships. By studying ecosystems at a variety of scales, ecologists can focus on international, regional or local issues. On a global scale, ecologists have mapped out world biomes which include tropical rainforests, temperate grasslands, deserts etc. At a regional scale, human and physical variations have produced ecosystems such as peat bags, sand dunes and estuaries. Each of the regional ecosystems is made up of smaller local ecosystems such as hedges, streams etc. However, none of these ecosystems can be viewed separately, because inputs, outputs and transfers operate among them.

The systems approach can, however, be used to study many more aspects of this course than just ecosystems i.e.:

Atmospheric energy budget Hydrological cycle Soils Nutrient cycles Population change Farming etc.

Key Summary An open system exchanges both energy and matter with its surroundings, a closed system exchanges energy but not matter, and an isolated system does not exchange anything with its surroundings.

// 1.1.4 //// Describe how the first and second laws of thermodynamics are relevant to environmental systems. //

Energy exists in a variety of forms (e.g. light, heat, chemical, electrical and kinetic). It can be changes from one form to another but cannot be created or destroyed. Any form of energy can be converted to any form, but heat can be converted to other form only when there is a temperature difference.

The behaviour of energy in systems is defined by the laws of thermodynamics. The first law states that energy can neither be created nor destroyed: it can only change forms. This means that the total energy in any system, including the entire universe, is constant and all that can happen is change in the form the energy takes. This law is known as the ‘law of conservation of energy’. In ecosystems, energy enters the system in the form of sunlight energy, is converted into biomass via photosynthesis, passes along food chains as biomass, is consumed, and ultimately leaves the ecosystem in the form of heat. No new energy has been created – it has simply been transformed and passed from one form to another. Heat is released because of the inefficient transfer of energy (as in all other systems).

Available energy is used to do work such as growth, movement and the assembly of complex molecules. Although the total amount of energy in a system does not change, the amount of available energy does (see diagram below). The transformation and transfer of energy is not 100% efficient: in an energy conversion there is less usable energy at the end of the process than at the beginning. This means there is a dissipation of energy which is then not available for work. The second law of thermodynamics states that energy goes from a concentrated form (e.g. the Sun) into a dispersed form (ultimately heat): the availability of energy to do work therefore diminished and the system becomes increasingly disordered.

(Diagram: the available energy in a system is reduced through inefficient energy conversions. The total amount of energy remains the same, but less is available for work. An increasing quantity of unusable energy is lost from the system as heat, which cannot be recycled into useable energy).

Energy is needed to create order (e.g. to hold complex molecules together). Therefore, as less energy becomes available, disorder (entropy) increases. In any isolated system, entropy tends to increase spontaneously. This universe can be seen as an isolated system in which entropy is steadily increasing so eventually, in billions of years time, no more available energy will be present. Natural systems can never actually be isolated because there must always be an input of energy for work (to replace energy that is dissipated). The maintenance of order in living systems requires a constant input of energy to replace that lost through the inefficient transfer of energy. Although matter can be recycled, energy cannot, and once it has been lost from a system in the form of heat energy it cannot be made available again.

Key Summary The first law of thermodynamics concerns the conservation of energy (i.e. energy can be neither created or destroyed); whereas the second law explains that energy is lost from systems when work is done, bringing about disorder (entropy). // 1.1.5 //// Explain the nature of equilibria. //

// 1.1.6 //// Define and explain the principles of positive feedback and negative feedback. // Feedback refers to the return of part of the output from a system as input, so as to affect succeeding outputs. There are two type of feedback:
 * Negative – feedback that tends to damp down, neutralise or counteract any deviation from an equilibrium, and promotes stability.
 * Positive – feedback that amplifies or increases change; it leads to exponential deviation away from an equilibrium.

// 1.1.7 //// Describe transfer and transformation processes // Matter and energy move through systems. If the movement does not involve a change of form or state, it is called a **transfer**; if it does involve a change of form or state, it is called a **transformation**. Both types of movement use energy: tranfers are simpler so they use less energy and are more efficient than transformations.

Transfers normally flow through a system and involve a change in location. For example, energy flows from one trophic level to the next through consumption of biomass.

Transformations either lead to an interaction within a system in the formation of a new end product, or they involve a change of state. Using water as an example, run-off is a transfer process and evaporation is a transformation process. In decay processes, dead organic matter entering a lake is an example of a transfer process; decomposition of this material is a transformation process. Energy is transformed in ecosystems: solar energy is transformed into chemical energy by photosynthesis and from chemical energy to kinetic energy and heat energy by respiration. // 1.1.8 //// Distinguish between flows (inputs and outputs) and storages (stock) in relation to systems. //

// 1.1.9 //// Construct and analyse quantitative models involving flows and storages in a system. //

// 1.1.10 //// Evaluate the strengths and limitations of models. //

Models may be in the form of practical examples such as an aquarium or terrarium, computer models, or diagrams. Although they are meant to represent real systems, in practice some models require approximation techniques to be used. For example, predictive models of weather systems may give very different results. In contrast, an aquarium may be a relatively simple ecosystem but demonstrates many ecological concepts.

All models have positive and negative attributes. Let’s consider the complex computer simulations used by scientists to model the effects of changes in the temperature of the Earth, and that can demonstrate anticipated changes to climate based on carbon emissions.

The advantages of these models are:
 * they allow scientists to predict and simplify complex systems
 * inputs can be changed and outcomes examined without having to wait for real events.
 * results can be shown to other scientists and to the public.

Disadvantages of such models are:
 * they may not be accurate – climate models are hugely complex in terms of numbers of factors involved in atmospheric systems, accuracy is lost in the process of oversimplification.
 * they rely on the expertise of the people making them
 * different people may interpret them in different ways.
 * vested interests may hijack them politically
 * any model is only as good as the data that goes in and these may be suspect
 * different models may show different effects using the same model

In particular, the complexity and oversimplification of climate models has led to criticism of these models.


 * // T //****// OK //**
 * // How does the system approach compare with the reductionist approach of conventional science? How does methodology compare between these two approaches? What are the benefits of using an approach that is common to other disciplines such as economics and sociology. //**