Physical Geography - Chapter 7 Sample Material

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ENVIRONMENTAL SYSTEMS MODELLING

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OVERVIEW

Being able to judge the potential environmental and social impacts of human actions and activities
is crucially important. One way of doing this is to build models of environmental systems. Starting by introducing the chief kinds of model, this chapter explains the workings of a selection of global,
regional and local models. Discussion of global models covers tutorial models, comprehensive
models and models of intermediate complexity. Tutorial or conceptual models, such as Lovelock’s
‘Daisyworld’ model, are mechanically simple, do not consider spatial differences and are designed
to demonstrate plausible processes in the Earth system.

Comprehensive models are three-dimensional, use explicit geography and have a high spatial and time resolution. Examples include the atmospheric general circulation models, dynamic global vegetation models and Earth Simulator, a gigantic computer designed to simulate just about everything environmental. Some of the more recent examples of comprehensive climate models attempt to couple atmospheric and oceanic circulations with biological and geochemical processes.

Earth System Models of Intermediate Complexity (EMICs) simulate interactions between several components of the natural Earth systems and form a useful bridge between comprehensive models and tutorial models, allowing climate simulations incorporating vegetation dynamics over timescales such as 10,000 years, or even glacial cycles. An example is the Climate and Biosphere Model (CLIMBER), applications of which include predicting the onset of the next ice age, exploring Holocene climatic changes and examining the threat of abrupt climatic change. Many models have local or regional components or are specifically developed to operate at a particular spatial and temporal scale. This chapter also provides examples of models that operate at these different scales.

LEARNING OUTCOMES

After reading this chapter, you may not be expert modellers but you should better appreciate:

The several types of model – hardware, analogue, conceptual and mathematical – and
how they are used in general terms
The use of mathematical models in studying environmental systems from a global
perspective
Global climate models and their role in investigating climatic change during the last
10,000 years and through the present century (global warming)
Dynamic global vegetation models and their value in predicting large-scale patterns and
changes in world vegetation
The impact of vast computing power on the potential of modelling projects
The use of models in probing issues concerning regional and local environmental
systems, such as changes in forest composition in a warmer world.

SUMMARY

Scientists have found several kinds of models helpful in understanding the environment and environmental change. They have built hardware models, conceptual models and mathematical models. Hardware models may be small and simplified versions of environmental systems – such as scaled-down replicates of river estuaries or a microcosmic reconstruction of the biosphere. Analogue models are akin to scale models but with more refinements, and include maps,
remotely sensed images and copies of dynamic natural systems where a different material substitutes for natural material – clay as an analogue of ice for example.

Conceptual models come in a variety of guises, but all of them are verbal, pictorial or numerical representations of an environmental system that suggest how the system is put together and how it works. Of all conceptual models, mathematical models are the most sophisticated and powerful. They come in three main varieties – stochastic models, statistical models and deterministic models – although many models are hybrids and use elements of, say, a deterministic model and a stochastic model. With the advent of fast computers with huge memories, mathematical models have come into their own. Today, scientists use them to study past, present and future changes in the globalecosystems, and to focus on changes at regional and local scales.

Global models can be highly simplified portrayals of the Earth system (tutorial models), richly detailed representations of the Earth system (comprehensive models), or
descriptions of the Earth system lying somewhere between very simple and highly complicated (models of intermediate complexity). Comprehensive models include climate models, the most refined of which are the various general circulation models used to predict climatic change (global warming for instance), and they include dynamic global vegetation models that simulate the global
patterns and dynamics of world vegetation. Earth Simulator, a huge and super-fast Japanese computer, is likely to run the most comprehensive of the models. Models of intermediate complexity try to bridge the gulf between model simplicity and model complexity. An example is the Climate and Biosphere Model (CLIMBER) used, for instance, to study world climates during the last 10,000 years. At regional and local scales, mathematical models have several
applications. They predict the changing composition of forests in response to
climatic changes.

QUESTIONS

1. Discuss the problems of making small -    scale hardware and analogue models of    environmental systems.
4. To what extent is ‘global warming’ the    result of natural climatic cycles?

2. For an ecosystem of your choice, describe    it in words, as a pictorial model and as a    box-and-arrow diagram.

5. What lessons can be learnt from models
    simulating change in community     composition?

3. Explain the use of atmospheric general
   circulation models in predicting the likely    climatic consequences of a nuclear war.