modeling and environmental science: an · pdf filedavid tenenbaum – geog 110 –...

David Tenenbaum – GEOG 110 – UNC-CH Fall 2005

Modeling and Environmental Science: An Introduction

• Environmental Science – It sounds like a modern idea, but if you view it broadly, it’s a very old idea:• Our ancestors’ survival depended on their

knowledge of the environment• “Science is a process, a way of knowing”• It results in conclusions, generalizations, and

sometimes scientific theories and even scientific laws• People often confuse the process of science with a

fixed set of beliefs – the results• BUT science does not lead to so much to a fixed

set of beliefs as to a set of beliefs that, at the present time, account for all known observationsabout a kind of phenomenon


Science Change• Science is a process of discovery, thus scientific ideas

change through time, and this can make applying the results of science frustrating. For example:1. Scientists cannot agree what is the best diet for

people.2. A chemical can be considered as dangerous in the

environment for a while, and then later be determined not be

3. Wild fire was considered to be undesirabledisturbance, and then it was decided that it is an important and necessary natural phenomenon

• It is more accurate to think of science as a continuing adventure with ever improving approximations of how the world works


How Does Science Work?• Science begins with “Observations” of the

world• From these observations, scientists formulate

hypotheses that can be tested• Modern science does not deal with things

that cannot be tested by observations, such as the existence of a supernatural being

• It is generally agreed today that the essence of the scientific method is “disprovability”

• A statement can be said to be scientific if someone can state a method by which it can be disproved


Scientific Statements• Let’s come up with a few scientific statements

• How could we disprove them?• For example: “Deforestation changes stream

water flow peaks and water quality”• This is a scientific statement as we can come

up with an experiment to disprove it or test if the above statement is true or false

• In some sense, progress in science is not so much limited by our ability to conceive of scientific statements, but our ability to come up with ways to test them …


Assumptions of Science1. Events in the natural world follow patterns that can be

understood through careful observation and analysis2. The basic patterns, or rules, that describe the behavior

of events in the natural world are the same everywhere3. Science is based on a type of reasoning known as

induction; it begins with specific observations about the natural world and extends to generalizations

4. Generalizations can be subjected to tests that may disprove them; if such a test cannot be devised, then a generalization cannot be treated as a scientific statement

5. Although new evidence can disprove existing scientific theories, science can never provide absolute proof of the truth of its theories


The Methods of Science

Yes NoObservation of Nature

(Context: Current scientific theories and

social values)

1

Form some Inferencesabout How We Think

Things Work

2

Create a Model that relates the Inferences

in Order to Explain the Observations

3Hypothesis Deduced

from the Model4

Test the Hypothesis 5

Perform Data Collection to Allow us

to Conduct the Test6

RejectHypothesis 7


Principles of Environmental Systems• Before we get to the systems view of the environment,

we need to set out some supporting ideas:1. The Earth is a dynamic and evolving system2. The Earth is the only suitable habitat we have3. Understanding is key to solving env. problems4. The Earth has been profoundly altered by life5. Sustained life on Earth6. The nature of population sizes through time7. Human activities cause changes in the environment8. Land-use/land-cover change tends to be cumulative9. The Principle of Environmental Unity


1. The Earth is a Dynamic and Evolving System

• The age of Earth: ~ 4.6 billion years

• Life on Earth: ~ 2 billion years

• Human ancestors: Several million years

• Our ancestors set the stage for the eventual dominationof human beings on Earth



• Matter and energy are constantly being transferred and are changing in form

• Energy: The Earth is nearly in a steady state in energy

I O

I = O

• That is, the Earth receivesenergy from the Sun and releases an equal amount of energy to space. There is no net gain or loss of energy for the Earth. This is not true over a day or year, but in the long term



• Matter: The Earth is almost a closed systemwhen it comes to matter

• That is to say, that much like energy if you compare how much is coming in versus going out over the long term, the difference is negligible

• Matter fluxes with respect to the magnitude of the Earth are quite small

I O

I = O


2. The Earth is the Only Suitable Habitat We Have

• Because the Earth is the only suitable habitat we have available to us (barring some future where we can successfully move elsewhere), we have a strong, motivated self-interest in how this dynamic and evolving system is going to change

• We know the resources of the Earth to be finite– Energy is more or less in a steady state– With respect to matter, the Earth is almost a

closed system• With this in mind …


3. Understanding is Key to Solving Environmental Problems

• When faced with problems concerning the environment, understanding environmental systems, their feedback cycles and rates of change are often the key to finding a solution:

• For example, let’s consider the sustainable use of forest resources: Given a particular tract of forested land, how much should we harvest each year in order to use the resource sustainably?

• What items of information do we need in order to make a decision here?



• Sustainable use of forest resources: What do we need to know?

1) How much timber do we have right now? (The current status of the pool)

2) How much timber will the forest add to the pool over time? (the rate of change)

3) How does current harvesting impact futuregrowth? (a feedback)

• With this sort of information in hand, we should be able to make a reasonable guess



• Depending on how much we decide to harvest, how quickly the forest regrows, and the feedback of harvesting, the forest might experience:

No change in the size of the pool

Pool is reduced in size

Pool is increased in size

Growth - Input Forest - Pool Harvest - Output


4. The Earth has been Profoundly Altered by Life

• The composition of the atmosphere has been altered by life for several billion years

• The atmospheric constituents of the Earth appear to have been relatively stable for millions of years

• This suggests that life regulates the conditions of its existence by stabilizing the atmosphere as well as by profoundly altering its constituents

• It’s for this reason that we should think of “The Earth as a Living Planet”


4. The Earth has been Profoundly Altered by Life

• Life is intimately tied to the cycling of elements through the atmosphere, not only by using the gases present in the air, but by controlling the constituent gases that make up the air (CO2, O2, H2O, various N species through nitrification & denitrification)

• Thus life effects the physical characteristics of the atmosphere, which effects the Earth’s surface, and rates of heating and cooling

• Life causes changes of chemistry in soils and rocks: Many mineral deposits are related to biological processes

• For example, the presence of limestone sediments is the result of photosynthesis; life on Earth caused the distribution and forms of water to be much more varied than it would have been on a lifeless planet


5. Sustained Life on Earth• Sustained life on the Earth is a characteristic of

ecosystems, not of individual organisms or particular populations– What are of the implications of this fact when we

attempt to study life on Earth?• No single organism, population, or species exists that

both produces all of its own food and completely recycles all of its own metabolic products– E.g. green plants can produce sugar from CO2 and

water, but no green plant alone can degrade woody tissue back to its original inorganic compounds. Those living things that degrade woody tissue, such as bacteria and fungi, do not produce their own food


5. Sustained Life on Earth• The minimal systems on Earth that exhibit a flow

of energy and a complete chemical cycling are composed of at least several interacting populations and their non-biological environment

• The smallest candidates for such minimal systems are what ecologists call ECOSYSTEMS

• The term ecosystem is applied to areas of all sizes, from the smallest puddle of water to the entire globe, provided they possess the properties described above (their scale can vary)


6. The Nature of Population Sizes through Time

• Individual populations are capable of rapid exponential growth, but this is rarely achieved in nature; control of populations is the norm– When the increase in the size of a population is a constant

percentage of the current population size, the growth is called exponential

– This can happen in a brief period of time in nature– Population size can be regulated by:1. Self-regulation as the birth, growth, and survival rates may

decrease as the population increases2. The influence of another population due to competition, e.g.

predator-prey control, competition for resources3. External factors, e.g. fire, tornados, etc.


7. Human Activities Cause Changes in the Environment

• All human activities, from the most primitive farming to the most recent technological innovations, cause some changes in our environment

• Since the Industrial Revolution, human beings have made many changes in our environment that are significant and detectable – e.g. The cutting of trees, land-use/land-cover

change expansion of cities, burning fossil fuels, agriculture, …


8. Land-use/land-cover Change tends to be Cumulative

• When we remove or replace the set of organisms at a particular location wholesale, this tends to produce a long-term effect

• Furthermore, as we do this over and over in the same places, and in ever increasing contiguous areas, these effects start to add up

• We have an obligation to future generationsto be mindful of this fact, as there are many examples in history where poor managementof land-use/land-cover (LULC) change has lead to disastrous consequences


9. The Principle of Environmental Unity

• In our environment, every action has more than one effect

• This is the Principle of Environmental Unity, i.e. everything affects everything else– For example: Cutting trees in a watershed

less evapotranspiration more runoff more erosion more nutrients in the river changes in water quality human health impacts

modeling and environmental science: an · pdf filedavid tenenbaum – geog 110 –...

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