Part 3: Tracking atmospheric levels of carbon dioxide (CO​2​) This portion of the lab focuses on the levels of atmospheric carbon dioxide (CO​2​) that scientists have measured at permanent observatories at South Pole at three different stations in different parts of the world. We will use these data to investigate (1) processes that might control variations in atmospheric CO​2​ levels during the year, and (2) processes that might explain the long-term trend in atmospheric CO​2​ levels. ______________________________________________________________________________ In 1958, scientists (notably Professor Charles Keeling) began to use high-precision equipment (e.g., infrared analyzers) to measure the abundance of atmospheric CO​2​ at selected sites around the globe. Among the initial sites were Mauna Loa, a 13,000-foot mountain on Hawai’i, and a station just a few miles from the South Pole. Measurements were begun at later times at other stations (e.g., 1973 for Barrow, Alaska). 1. Familiarize yourself with the locations of these three measuring stations. 2. Examine the three graphs. The curve on each graph connects monthly measurements, though it’s difficult or impossible to see the points for individual months at this scale. A. What is the variable being measured? B. What units are used to express this variable? 3. Look at the three graphs again. Although they represent different time intervals and none show a perfectly smooth curve, all of them show the same long-term pattern. Describe this pattern in 1-2 sentences . The numbers below show the monthly (numbered 1 through 12) readings for 2003 and 2004 at each station. The last column is the annual average. MLoa​ 1 2 3 4 5 6 7 8 9 10 11 12 avg 2003 374.7 375.6 376.1 377.6 378.4 378.1 376.6 374.5 373.0 373.0 374.4 375.7 375.6 2004 376.8 377.4 378.4 380.5 380.6 379.6 377.8 375.9 374.1 374.2 375.9 377.5 377.4 Barrow​ 1 2 3 4 5 6 7 8 9 10 11 12 avg 2003 379.0 382.3 381.4 381.4 382.2 380.8 371.0 364.7 368.3 372.5 378.6 382.5 377.0 2004 382.6 383.2 382.2 383.8 383.5 380.5 371.8 366.5 367.9 373.5 379.2 382.3 378.1 S Pole​ 1 2 3 4 5 6 7 8 9 10 11 12 avg 2003 371.9 371.8 371.7 372.0 372.3 372.6 373.0 373.4 373.9 373.8 373.6 373.6 372.8 2004 373.6 373.4 373.8 373.9 374.1 374.5 374.8 375.4 375.5 375.6 375.5 375.2 374.6 4. Plot the ​2004 results​ from all three stations on the same graph below. Connect the points for each site with a smooth curve, and label each curve with the site name. Although the data you have graphed are several years old (recall that the ​current level of CO​2 in Earth’s atmosphere is more than 406 ppm​), the patterns would be similar for more recent data. Each of the three curves should clearly show a cycle known as a ​short-period oscillation. Our goal is to determine the cause of these oscillations. First, let’s analyze some aspects of the curves you plotted. 5.​ In what months of 2004​ were the ​maximum​ and ​minimum ​values of CO​2​ recorded at each station? Maximum (month) Minimum (month) Mauna Loa Barrow South Pole 6. What is the ​amplitude​ of the oscillation? In other words, what is the difference (in ppm CO​2​) of the maximum and minimum value at each station? Mauna Loa: _______ ppm Barrow: _______ ppm South Pole: _______ ppm 7. Interpret your results (in terms of the geographic locations of the three sites) to answer the following questions. A. Why do the oscillations occur? B. Why do the oscillations peak when they do? C. Why is the amplitude of the South Pole station so much smaller than that of the other two? N​ow let’s look farther back in time at atmospheric CO​2​ levels​. Though precise measurements only began in 1958, scientists have been able to sample “fossil air” from the early 1900s and even the 1800s in tightly sealed bottles of wine of known vintage, and in old brass buttons with sealed air gaps. They have also been able to sample and date fossil air in ice layers. The Law Dome ice cores in Antarctica sampled ice over a thousand years old (below). 6. The cores from Law Dome show that the amount of CO​2​ in the atmosphere was fairly constant from 1000 A.D. until about what year? ____________ 7. Thinking back on your world history, why did CO​2​ emissions begin to increase around that time? 8. How did the ​rate of increase​ in CO​2​ emissions change at that time, and how can you tell from the graph? 9. List ​three​ human activities that add CO​2​ to the atmosphere. Part 4: Sea Level Rise A. Melting ice and sea level change The table below shows the volumes of Earth’s present-day glaciers and the potential sea rise, expressed in meters, if all of the ice at each location melted. Note that potential sea level rise is left blank for Greenland. In this part of the lab, you will calculate how much sea level would rise if all the ice on Greenland melted. ​You will be making several assumptions in order to simplify these calculations. Table 1.​ Estimated potential maximum sea level rise from the total melting of present-day glaciers. Location Volume (km​3​) Potential sea level rise (m) East Antarctic ice sheet 26,039,200 64.80 West Antarctic ice sheet 3,262,000 8.06 227,100 .46 Antarctic Peninsula Greenland All other ice caps, ice fields, and valley glaciers Total 2,620,000 180,000 .45 32,328,300 Modified from Williams and Hall (1993). See also ​http://pubs.usgs.gov/fs/2005/3055/​. km​3​, cubic kilometers; m, meters] Follow these steps to make your calculations. 1. Convert the volume of ice to the volume of water To determine how much sea level would rise as a result of a given volume of ice melting, you first need to calculate the volume of water that would result from melting. Ice is less dense than water. ​ It has a density that is 0.9 times (90%) that of water. Therefore, when one km​3​ of ice melts, it will decrease its volume by 10%. Thus, the conversion factor you need is: ​1 km​3​ of ice = 0.9 km​3​ of water a) Volume of ice in Greenland ice sheet: _________________________ km​3 b) Calculate the ​volume of water​ using resulting from melting of the Greenland ice sheet ​(show work and units!) Volume of water ________________________ km​3 2. Calculate sea level rise The surface area of the oceans basins​ is 361,000,000 km​2 a) Sea Level Rise = Volume of Water (km​3​)____ ​ Surface Area of Ocean (km​2​) = ​_____________km​3 361,000,000 km​2 = __________km Now fill in the blank areas of the table (potential sea level rise from melting Greenland’s ice and the potential total sea level rise if all of Earth’s glaciers melted). Now convert your answer to units with which you may be more familiar. a) Sea level rise in meters (m): ________________ (​Note: 1 km = 1,000 m​) Show your work. b) Sea level rise in feet (ft.): ___________________ (​Note: 1 m = 3.28 ft​.) Show your work. B. Local sea level rise In the previous section we considered how much ​global sea level ​would rise as the result of melting glaciers. In contrast,​ local​ sea level rise is affected by several factors including topography and whether a coastal area is sinking or being uplifted. Do the activities below and then answer the questions on the next page. 1. Fill your container 1/3 with water. 2. Place ruler in the water so that it is exactly vertical. 3. Draw a picture of the ruler and cup exactly as you see it: 4. Tilt the ruler so that it is at approximately a 45 degree angle. 5. Draw a picture of the ruler and cup exactly as you see it: Don’t use this quesiton: Questions: 1. If you were to add more water to the cup which would record a higher level of water, the vertical ruler or the tilted ruler? ______________________ 2. Which covers a greater area, the tilted ruler or the straight ruler? Why? 3. Which coastal area, A or B, shown on the figure (note that this is cross-section view, from the side) below has a greater chance of disappearing if sea level was to rise 20 feet? ________ Use what you learned in the activities above to explain.
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