Chapter 6 Global Climate Change Section 2 Ho w Do Earth’s Orbital Variations Affect Global Climate? What Do You See? Learning Outcomes In this section, you will Learning• GoalsText Outcomes Think About It In this section, you will When it is winter in New York, it is summer in Australia. • Understandthat Earth has an • Why are the seasons reversed in the Northern and axial tilt of about 23.5°. Southern Hemispheres? • Usea globe to model the seasons on Earth. Record your ideas about this question in your Geo log. Be • Investigateand understand the prepared to discuss your responses with your small group cause of the seasons in relation and the class. to the axial tilt of Earth. • Understandthat the shape of Investigate Earth’s orbit around the Sun is an ellipse, and that this shape This Investigate has five parts. In each part, you will explore influences climate. different factors that cause Earth’s seasons. • Understandthat insolation Part A: What Causes the Seasons? An Investigation on Paper to Earth varies as the inverse square of the distance to 1. Create a model of Earth by completing the following. the Sun. a) In your log, draw a circle about 10 cm in diameter in the center of your page. This circle represents Earth. 650 EarthComm EC_Natl_SE_C6.indd 650 7/13/11 9:31:54 AM Section 2 How Do Earth’s Orbital Variations Affect Global Climate? b) Add Earth’s axis of rotation, plane • Now, mark off 10° increments of orbit, the equator, and lines of starting from the equator and going latitude, as shown in the diagram, to the poles. You should have eight by completing the steps below. marks between the equator and pole for each quadrant of Earth. • Use a ruler to draw black lines that connect the marks opposite one another on the circle, making lines that are parallel to th e equator. This will give you lines of latitude in 10° increments so you can locate your latitude fairly accurately. Note that the lines will not be evenly spaced from one another because latitude is measured as an angle from the center of Earth, not a linear distance. 2. Imagine that the Sun is directly on the left in your drawing. • Put a dot in the center of the circle. a) Draw horizontal arrows to represent Draw a dashed line that goes directly incoming Sun rays from the left side up and down from the center dot of the paper. to the edge of the circle. Use your protractor to draw a horizontal line 3. Assume that it is noon in that is perpendicular to the vertical your community. line and passes through the center a) Draw a dot where your community’s dot. This horizontal line represents latitude line intersects the edge of the the plane of Earth’s orbit. circle on the left. This dot represents • Use a protractor to measure 23.5° your community. Explain why this from the vertical dashed line. Use represents noon. a blue pen or pencil to draw a line through the center of “Earth” at 23.5° b) At any given latitude, both north to the dashed line. This blue line and south, are the Sun’s rays striking represents Earth’s axis of rotation. the Northern Hemisphere or the Southern Hemisphere at a larger • Use your protractor to draw a red angle relative to the plane of orbit? line that is perpendicular to the axis of rotation and passes through the c) Which do you think would be center dot. This red line represents warmer in this drawing—the the equator of Earth. Northern Hemisphere or the • Label the Northern and Southern Southern Hemisphere? Write down Hemispheres. your hypothesis. Be sure to give a • Next, you need to add lines of reason for your prediction. latitude. To do this, line your d) What season do you think this is in protractor up with the dot in the the Northern Hemisphere? center of your circle so that it is parallel to the equator. 651 EarthComm EC_Natl_SE_C6.indd 651 7/13/11 9:31:54 AM Chapter 6 Global Climate Change 4. Now consider what happens six months 2. Set up a light and the globe as shown. later. Earth is on the opposite side of its orbit, and the sunlight is now coming from the right side of the paper. a) Draw horizontal arrows from the right side of the paper to represent incoming rays from the Sun. 5. Again, assume that it is noon in your community. a) Draw a dot where your community’s latitude line intersects the edge of 3. Position the globe so that its axis of the circle on the right. Explain why rotation is tilted 23.5° from the vertical, the dot represents your community and the North Pole is pointed in the at noon. direction of the light source. b) Are the Sun’s rays striking the 4. Turn on the light source. Northern Hemisphere or the Southern Hemisphere more directly? a) Record the initial temperature. Then record the temperature on the c) Which do you think would be thermometer every minute until the warmer in this drawing—the temperature stops changing. Northern Hemisphere or the Southern Hemisphere? Explain your answer. 5. Now position the globe so that the axis of rotation is again tilted 23.5° from the d) What season do you think this is in vertical but the North Pole is pointing the Northern Hemisphere? away from the light source. Make sure Part B: What Causes the Seasons? the light source is the same distance An Investigation With a Globe from the globe as it was in Step 4. 1. Test the hypothesis you made in a) Record the temperature every minute Part A about which hemisphere would until the temperature stops changing. be warmer in which configuration. Find your community on a globe. 6. Use your observations to answer the Using electrical tape, tape a small following questions in your log: thermometer on it. The thermometer a) What is the difference in the average bulb should be over your community temperature of your community and the electrical tape should cover it. when the North Pole was pointing toward the light source and when it Use only alcohol thermometers. Place a soft cloth was pointing away? on the table under the thermometer in case it b) What caused the difference falls off. Be careful not to touch the hot lamp. in temperature? 652 EarthComm EC_Natl_SE_C6.indd 652 7/13/11 9:31:54 AM Section 2 How Do Earth’s Orbital Variations Affect Global Climate? Part C: What Would Happen if Earth’s Axial Tilt Changed? An Investigation on Paper 1. Repeat the investigation you did in Part A, except this time use an axial tilt of 10°. a) Compared to an axial tilt of 23.5°, would your hemisphere experience a warmer or colder winter? 4. Draw a straight line from one edge of b) Compared to an axial tilt of 23.5°, the circle that you just made to the would your hemisphere experience opposite edge, through the center of the a warmer or colder summer? circle. This line represents a diameter of 2. Repeat the investigation you did in the circle. Mark two points along the Part A, except this time use an axial diameter, each a distance of 20 cm from tilt of 35°. the center of the circle. Put the loops of the rope over the two points, hold them a) Compared to an axial tilt of 23.5°, in place with two dowels, and use the would your hemisphere experience chalk to draw a curve on one side of a warmer or colder winter? the straight line. Move the chalk to b) Compared to an axial tilt of 23.5°, the other side of the line and draw would your hemisphere experience another curve. a warmer or colder summer? a) What type of figure have Part D: Earth’s Elliptical Orbit Around you constructed? the Sun 1. Tie small loops in each end of a rope, as shown in the diagram. 2. Pick a point in about the middle of the floor, and put the two loops together over the point. Put a dowel vertically through the loops, and press the dowel tightly to the floor. 3. Stretch out the rope from the dowel until it is tight, and hold a piece of chalk at the bend in the rope, as shown in the diagram. While holding the chalk tight against the rope, move the chalk around the dowel. a) What type of figure have you constructed? 653 EarthComm EC_Natl_SE_C6.indd 653 7/13/11 9:31:55 AM Chapter 6 Global Climate Change 5. Using different colors of chalk, make Avoid contact with the hot light bulb. Do not a few more curved figures in the same look directly into the light. way. Choose sets of dowel points that are farther and farther away from 4. Turn on the light bulb, and turn off the the center. lights in the room. If the room is not dark enough to see the image on the a) Describe the shapes of the figures wall, close any curtains or shades, or you constructed. Make sketches in cover the windows with dark sheets your Geo log. or blankets. b) What would be the shape of the 5. With chalk, trace the edge of the image curve when the dowel points are the hole makes on the wall. spaced a distance apart that is just equal to the length of the rope a) Measure and record the length of the between the two loops? sides of the image you marked with the chalk.