NetLogoGreenHouse or Climate_change Community model
20-Jan-2010COLQ 201, Prof. Howard, Tulane University4 The two models What is the difference between them?
20-Jan-2010COLQ 201, Prof. Howard, Tulane University5 A first look at the interface What controls do you see in the interface? Do you see anything that is not consistent with the 'standard' interface that we looked at last time? Stop button. What is albedo? The albedo of an object is the extent to which it diffusely reflects light from light sources such as the Sun. It is therefore more specific than the term reflectivity.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University6 The information tab What is it? What do the colors mean? The earth is rose colored. On the earth surface is a green strip. Above it is a blue atmosphere, with black space at the top. Yellow arrowheads stream downward representing sunlight energy. Each red dot represents the energy of one yellow sunlight arrowhead. The temperature of the earth is related to the total number of red dots. Infrared energy is represented by a magenta arrowhead.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University7 What happens Some of the sunlight reflects off clouds and more can reflect off the earth surface. If sunlight is absorbed by the earth, it turns into a red dot, representing heat energy. The red dots randomly move around the earth. The temperature of the earth is related to the total number of red dots. Sometimes the red dots transform into infrared (IR) light that heads toward space, carrying off energy. The probability of a red dot becoming IR light depends on the earth temperature. When the earth is cold, few red dots cause IR light; when it is hot, most do. Each IR arrowhead carries the same energy as a yellow arrowhead and as a red dot. The IR light goes through clouds but can bounce off CO2 molecules.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University8 The controls The "reset" button If "Use-My-Start-Values" is switched off, "reset" sets the model to a reasonable approximation of the situation in the year If "Use-My-Start-Values" is switched on, "reset" uses the values in the "year," and "temp" sliders. The "sun-brightness" slider controls how much sun energy enters the earth atmosphere. A value of 1.0 corresponds to our sun. Higher values allow you to see what would happen if the earth was closer to the sun, or if the sun got brighter.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University9 Controls, cont. The "albedo" slider controls how much of the sun energy hitting the earth is absorbed. The earth's albedo is about 0.6. If albedo is 1, the earth reflects all sunlight. This could happen if the earth froze and is indicated by a white surface. If albedo is 0, the earth absorbs all sunlight. This is indicated as a black surface. You can add and remove clouds with the FORM CLOUDS and REMOVE CLOUDS buttons. Clouds block sunlight but not IR. You can add and remove greenhouse gasses, represented as CO 2 molecules. CO 2 blocks IR light but not sunlight. The buttons add and subtract molecules in groups of 25 up to 150.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University10 Another control Follow a single sunlight arrowhead using the WATCH SUNRAY button. This is easier if you slow down the model using the slider at the top. What happens to the arrowhead when it hits the earth? Describe its later path. Does it escape the earth? What happens then? Do all arrowheads follow similar paths?
20-Jan-2010COLQ 201, Prof. Howard, Tulane University11 Exercises Explore the effect of albedo: change it while keeping everything else constant (sun = 1, no clouds, no CO 2 ). Be sure to run the model long enough for the temperature to settle down. Does increasing the albedo increase or decrease the earth's temperature? Explore the effect of sun brightness: change it while keeping everything else constant (albedo = 0.6, no clouds, no CO 2 ). What happens to the temperature? It should rise quickly and then settle down around 50 degrees. Why does it stop rising? Why does the temperature continue to bounce around? When the temperature is constant, there about as many incoming yellow arrowheads as outgoing IR ones. Why?
20-Jan-2010COLQ 201, Prof. Howard, Tulane University12 Exercises, cont. Explore the effect of clouds: change it while keeping everything else constant (sun = 1, albedo = 0.6, no CO 2 ). Explore the effect of adding CO 2 : change it while keeping everything else constant (sun = 1, albedo = 0.6, no clouds). What is the cause of the change you observe. Follow one sunlight arrowhead. Add clouds and CO 2 to the model and then watch a single sunlight arrowhead. What is the highest temperature you can produce?
20-Jan-2010COLQ 201, Prof. Howard, Tulane University13 With your neighbor … What are the agents? What rules do they follow? What are the patches? What rules do they follow?
20-Jan-2010COLQ 201, Prof. Howard, Tulane University15 The NetLogo world … is a two dimensional world that is made up of turtles, patches and an observer. The patches create the ground in which the turtles can move around on and the observer is a being that oversees everything that is going on in the world.
20-Jan-2010COLQ 201, Prof. Howard, Tulane University16 Next time Biology: flocking, herding & schooling: Boids, MyFlocking