Geological Sciences 101 Lab #9 - Records of Past and Present Climate Change INTRODUCTION This lab has several parts. First, we will access a number of paleoclimate data sets acquired by drilling into layers of ice preserved in Arctic and Antarctic ice sheets. We will plot them with Excel and examine the changes in temperature and atmospheric composition that occurred during the last ice age. We will also examine changes in sea level recorded by tropicl coral reefs. After graphing the data to understand their temporal changes will use ArcView to examine these changes spatially. Finally, we will explore modern changes in atmospheric composition that are due to anthropogenic influence. PART I - GATHERING DATA ON PAST CLIMATES First we will work with data collected by researchers who have drilled into Arctic and Antarctic ice caps to learn about Earth's past climate changes. Just as layers of rock preserve the record of conditions on the ancient Earth, layers of ice preserve a great deal of information about conditions over the last 200,000 years. Especially important are the tiny samples of ancient atmosphere preserved in bubbles trapped in the ice, as well as the chemical composition of the ice itself, which contains a record of temperature variation. You will gather data from the Vostok site in Antarctica, where a joint French-Russian team drilled a 2000 meter long ice core, containing paleoclimate information back almost 250 thousand years before present. We will also look at sea level data from part of this time interval. The record of ancient sea level is obtained from dating fossil corals found in the world's coral reefs. Since many corals must live just below the surface of the ocean they provide a good measure of ancient sea levels. Getting & Graphing the Data PLEASE NOTE: If you are using a computer in Upson, you must save all your work on a floppy diskette on the A: drive. You will use your browser to visit the National Geophysical Data Center in order to download data on climate change. These data are posted and utilized by the world's leading researchers in order to study how climate has changed in the geologic past, and to predict how it might change in the near future. Use your browser to go to: • http://www.ngdc.noaa.gov • Once there, click on the "Paleoclimatology" link. • On the Paleoclimate page, choose the "Paleoclimate Data" link. • In the section titled, "Obtaining Data by Discipline," choose "Ice Cores." • On the ice core page, scroll down to the link, "Download Ice Core Data." 1 Now you have accessed the data server (note that it has no graphics, just lists of files and folders). Click on the word "antarctica." • From this new directory, choose "vostok." Finally, you have found the data files. You will download two files: • Click on Vostok.Dd • Use the "Save As" command to store the file on the A drive (note--make sure you don't save the file in HTML format, save it as text). • Use the back button to return to the file list. Save co2.dat in the same way. Open the files with Excel: • Find Excel under the Start button. Start Excel. • Use the open command to import the file Vostok.Dd. You may have to switch to "All Files (*.*)" in the "Files of Type" box, if you don't see your files listed in the Open window. • In the Text Import Wizard window, choose "Delimited" from the Original Data Type window. Click Next. • Choose "Space" in the Delimiters box. Click Finish. You should have a spread sheet with a whole bunch of text placed in boxes. Scroll down below the text and make sure that you also have eight columns of data. You may delete everything above the rows that contain the labels "column1," "column2," etc. To do so, use the Delete command under the Edit window (or right-mouse). You should also delete columns 1-5 and column 7. You may also delete any extra text that is still lying around. • Rename column6 "Age (kyr)." These data are the ages of the samples, in thousands of years (so 0.014 kyr = 14 years before present; 10 kyr = 10,000 years before present). • Rename column8 "Temp (C) +/- present." These data are temperature measurements, made relative to present average temperature (so -0.07 is 0.07 degrees celsius colder than the average temperature now). • Now open co2.dat. Use the same procedure--"delimited," "space," etc. We only need two columns from this data set as well. Delete everything except the column that begins with 4050 and the column that begins with 274.5. • Label the 4050 column "Age (yr)." This is the age of the sample in years before present. • Label the 274.5 column "CO2 (ppm)." These data are measurements of the amount of carbon dioxide gas in the atmosphere throughout the past 150,000 years. Ppm stands for "parts per million." A measurement of 274 ppm means that for every million molecules of atmosphere, 274 of those are carbon dioxide. 2 • Copy the two columns of CO2 data and paste them into the Vostok.Dd spreadsheet beside the two previous columns of data. There is one small inconsistency between these two data sets: the temperature data is given in thousands of years while the CO2 data is given in years. We want to plot both data sets on a single graph, so we'll have to adjust the age of the CO2 data to be consistent with the temperature data. • Insert a column between the Age (yr) and CO2 (ppm) columns. • Divide the age data by 1000 so that it is in ka (thousands of years). Do this by typing an equals sign, then click on the first age value, then type "/1000" and hit enter. You may then drag this formula down to fill all the cells below. Label this column "Age (kyr)." • Save your work on the A drive. Graph the data: • Begin with temperature. Use the cursor to select the two columns of temperature data, "Age (kyr)" and "Temp (C) +/- present." • Use the graph tool to insert a graph on this page of your Excel spreadsheet. Choose a scatter plot. • Label the graph "Vostok Ice Core," label the X-axis "Age (kyr)," label the Y-axis "Temp (C) +/- present." • Re-scale the X-axis so that is has a minimum value of 0 and a maximum values of 250, in increments of 10 ka. • Now add the CO2 data to the temperature graph. Under the Chart menu choose Add Data. Use the cursor to select the new data to add (Age (kyr) and CO2). Note that this squashes all of your temperature measurements (because the range of values in the two data sets is very different). We'll fix this by switching the CO2 data to a "secondary axis." • Double-click on any CO2 data point on your graph in order to access the "Format Data Series" screen. • Choose "Axis," and tell it to plot the series on the secondary axis. • Once this is done, double-click on the secondary axis and re-scale the CO2 data from 150 - 300. • Make your graph "look pretty," and print it. 3 QUESTIONS 1) Examine the record of CO2 and temperature over the last 170,000 years. Are the trends similar or different? Describe. What can you conclude about the behavior of CO2 and temperature over time? 2) Ice ages are identified by their colder temperatures. When was the last ice age? What was the temperature difference in Antarctica at that time with respect to the present temperature? What was the atmospheric CO2 concentration during the last ice age? 3) Are there any other ice ages recorded in this data? How many? When? 4) When Earth enters an ice age does the climate cool relatively quickly or relatively slowly? When it warms is it fast or slow? 5) Calculate the rate at which atmospheric CO2 increased (in ppm/year) during the warming period that followed the last ice age (show your work). PART II - COMPARISONS WITH OTHER DATA SETS • Open the 101_climate.xls file from your diskette. Begin with the GRIP data. These are also temperature measurements made from and ice core in Greenland. • Examine the two graphs; the first shows the entire ice core record, the second graph shows only the last 40,000 years of the data. 6) Do the same ice ages appear in both the Greenland and Antarctic data sets? Was the temperature change in Greenland more/less/the same during the last ice age as it was in Antarctica? 7) Examine the graph of the last 40,000 years. Describe the climate from 10,000 years to the present. Describe the climate prior to 10,000 years ago. 8) Ancient humans switched from a hunter-gatherer style of existence to and agriculture-based existence approximately 8,000 years ago. Would agriculture have been a viable lifestyle prior to this time? Why/why not? • Switch to the Mauna Loa CO2 measurements. These are modern analyses made in the unpolluted central Pacific ocean. The data record monthly changes in CO2 from March 1958 - December 1995. • Examine the two graphs, the monthly CO2 data and the yearly average CO2 concentrations from 1958-1995. 9) Describe the monthly CO2 data. What process is responsible for the pattern you observe? 10) Calculate the rate of change in the yearly average CO2 from 1958 to 1995 (in ppm/year). Show your work. Compare this rate with the post-ice age change you calculated above. Outline a hypothesis that explains your result.