EAR 203

Name: ________________________Date: _________________________Block: _____

EAR 203 EARTH SYSTEM SCIENCESYRACUSE UNIVERSITY

LAB 2A – DAISYWORLD – SIMULATION 1

1. Description of DaisyWorld – Parts of this lab are modified from a lab designed by R.M. MacKay based on the description of DaisyWorld from Hardisty et al. (1993).

Scientists commonly use models that oversimplify complex real world situations to explore the range of possible relationships between the components of a system. DaisyWorld is a good example of a very simple model that explores the relationship between biota and their environment under a set of forcing conditions. This model builds upon the one described within your textbook by adding a population of dark (low albedo) daisies to the light (high albedo) population.

As with all models, it is important to understand the assumptions and boundary conditions associated with the DaisyWorld model. These include:

Boundary Conditions:

1. The planet has a transparent atmosphere, without clouds or greenhouse gasses.2. The planet is flat so there are no seasons or latitude related variations in the solar radiation

received by the surface. Therefore, changes in surface temperature are solely the result of changes in the solar luminosity and surface albedo.

3. Only two species of plants exist: light daisies and dark daisies. Light daisies have an albedo greater than the grey soil; conversely, dark daisies have an albedo lower than that of the grey soil.

4. Daisies are grazed in a non-selective manner by herbivores that recycle organic matter in the system.

Assumptions:

1. Global temperature depends only on luminosity of the sun and planetary albedo.2. Planetary albedo is the sum, weighted by area, of the dark (0.25) and light colored (0.75) daisies

and bare ground (0.5).3. The amount of fertile land available for daisy growth depends on the total amount of fertile land on

the planet (which is fixed) and the present coverage of daisy growth.4. The rate of population change for each species of daisy is dependent on the potential birth rate for

that species, the death rate, and the amount of fertile land available.5. The birth rate for both species depends on the local temperature.6. The local temperature is dependent on the difference between the global and local albedo, as well

as the global temperature.

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2. Below is a systems diagram for the DaisyWorld Model System.

Assignment – Please label whether the couplings depicted above are negative or positive in the boxes provided. The coupling between Luminosity and Global average temperature is completed as an example.

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3. Analysis of DaisyWorld using feedback loops.

Example 1. Analysis of Light Daisy coverage using feedback loops –

Light colored daisies create a local albedo that is higher than bare ground, so as the light daisy population increases the planetary albedo increases and the planet temperature decreases.

*There is a positive coupling between daisies and albedo.*There is a negative coupling between albedo and temperature.

Therefore, this feedback loop is negative.

Daisy growth is defined by a maximum and minimum temperature at which daisies can grow with a middle optimum temperature. This relationship defines a parabolic shape.

To the left of the optimum temperature towards colder values on the graph to the left, an increase in surface temperature results in an increase in daisy coverage.

To the right of the optimum temperature towards the warmer vales on the graph, increasing the surface temperature results in a decrease in daisy coverage.

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When the relationship of daisy coverage on temperature and temperature on daisy growth are combine into one graph the feedback loops of this system can be explored further.

To the left of the graph’s peak, an increase in temperature causes an increase in daisy growth, resulting in an increase in albedo, and a resultant decrease in temperature. This is a stable, negative feedback loop.

To the right of the graph’s peak, an increase in temperature causes a reduction in daisy coverage, resulting in a decrease in albedo and a resultant increase in temperature.This is an unstable, positive feedback loop.

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4. Analysis of dark daisy coverage using feedback loops. Please fill in the blanks below where appropriate.

Dark daisies absorb more sunlight than bare ground, so as the dark daisies grow, the

planetary albedo and the planetary temperature ______ .

The reverse is also true, as dark daisies die, the planetary albedo and

the planetary temperature .

This forms a _____ feedback loop.

Following the example given for light daisies in section 3, please sketch a graph showing the relationship between dark daisy coverage and average surface temperature. Describe the two feedback loops presented in this graph.

Graph- Description-

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Combine the two graphs present above in section 4 onto one graph. Describe the feedback loops to the right and left of the optimum growing temperature for dark daisies.

Feedback Loops- Description-

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5. Running the DaisyWorld Model http://www.atmosedu.com/physlets/DaisyWorld/Daisy.htm - use the Java applet to complete the following assignment. (If this does not work, go to: Control Panel Security Add Site.)

Run the DaisyWorld model, varying the solar luminosity (L) from 0.6 – 1.3 over the increments given below. Input the data into an Excel spreadsheet and create the graphs you need to answer the questions below.

Solar Luminosity

(L)

Average Planet Temp

(oC)

Area of Light Daisies

(%)

Area of Dark Daisies (%)

Planetary Albedo (A)

Absorbed Solar

[L*(1-A)]0.600.630.650.700.750.800.850.901.001.051.101.151.171.201.231.251.271.30

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Now repeat the steps above but click the Dead Planet box. This will model the conditions of the planet without daisies.

Solar Luminosity (L)

Average Planet Temp (oC)

Planetary Albedo (A)

Absorbed Solar[L*(1-A)]

0.600.630.650.700.750.800.850.901.001.051.101.151.171.201.231.251.271.30

Graphs – Look at the graphs created in the spreadsheet. You should have the following graphs:

- Average Planet Temperature versus Solar Luminosity- Area of Dark and Light Daisies versus Solar Luminosity- Area of Dark Daisies, Light Daisies, and Bare Ground versus Average Planet Temperature- Planetary Albedo versus Solar Luminosity

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Analysis Questions:

1. What is the smallest value “L” that initiates daisy growth?

2. What is the largest value “L” before daisies stop growing?

3. Which type of daisies are the first to begin to grown and why (hint- you may want to take a look at the feedback loops in previous sections)?

4. Which type of daisies are the last to die out and why?

5. Why is there an inverse relationship between dark and light daisy growth when plotted versus solar luminosity?

6. What effect does the presence of daisies have on the albedo and local temperature with increasing solar luminosity and how might this relate to your answer in to question 5?

7. Compare the behavior of the Dead Planet and DaisyWorld. (Be sure to look at the graph of Average Daily Temperature versus Solar Luminosity and include discussion of the feedback loops).

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8. Based on the information in these graphs write an executive summary describing how DaisyWorld self-regulates its planetary temperature. Your summary should:

Have an introductory paragraph describing the purpose of the Model and the basic assumptions made by the model.

Explain the information on each graph. Compare the behavior of the Dead Planet to that of DaisyWorld Explain how DaisyWorld self-regulates its planetary temperature. Comment on how DaisyWorld applies to the faint young sun paradox. (See your text or do a

web search to find out more about the faint young sun paradox.) Comment on the idea that very small changes in climate forcing can result in large changes

in the climate state of a planet. For example, some feel that are biggest concern regarding future climate change is not so much the gradual alterations to global temperature but the potential for large shifts in climate state brought about by some unforeseen mechanism.

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