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UA GEOG 101 - GEO Lab 6

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GEOG 170A1 Earth’s Environments: Introduction to Physical GeographyClimate Change LabPart 1: Atmospheric Carbon Dioxide ConcentrationsScientists at the Scripps Oceanographic Institution and the National Oceanic and AtmosphericAdministration (NOAA) have been measuring the concentration of atmospheric CO2at MaunaLoa in Hawaii since the late 1950s. On the next page is a graph (Figure 1) that shows themonthly atmospheric CO2concentration data (in units of parts per million, ppm), starting inMarch of 1958 and ending in August of 2019 (the latest date for which data are available). Ifyou’d like to look at the data yourself, you can find it here: https://www.esrl.noaa.gov/gmd/ccgg/trends/.Using the graph in Figure 1, please answer the following questions:1.A. Approximately what was the level of atmospheric CO2in 1958, when measurements firstbegan (give your answer in unit of parts per million, ppm)?1.B. Approximately what was the level of atmospheric CO2as we started 2019 (give your answerin unit of parts per million, ppm)?1.C. Based on your answers above, approximately how much have CO2levels in the atmosphereincreased in the last approximately 60 years (give your answer in unit of parts per million,ppm)?1.D. Observing the graph, notice that the monthly values have a regular repeated cycle overthe course of the year, rising to their maximum annual value in late April or early May, andthen dropping to their lowest annual value around late September or early October. Makingobservations from the graph, approximately how large (give your answer in unit of parts permillion, ppm) is this annual cycle?1.E. Based on Wednesday’s lecture: What is the cause of the regular monthly cycle? And, whatis the cause of the long-term increase in CO2?11950 1960 1970 1980 1990 2000 2010 2020YEAR300320340360380400420CO2 CONCENTRATION (ppm)2015 2016 2017 2018 2019 2020400405410Figure 1: Monthly carbon dioxide (CO2) concentrations (in units of parts per mil-lion, ppm) in the atmosphere at Mauna Loa in Hawaii. The inset box shows azoomed in zoomed-in version of the same data between 2015 and now. Data are fromhttps://www.esrl.noaa.gov/gmd/ccgg/trends/2Part 2: Future carbon dioxide levels12.A. Humans currently put an additional 40 gigatonnes of CO2into the atmosphere per year.About half of this CO2(so, 20 gigatonnes) is absorbed by the oceans and the biosphere, andhalf (so, the other 20 gigatonnes) remains in the atmosphere. If this continues every year forthe next 80 years (that is, every year from now until the year 2100), how many more gigatonnesof CO2will be in the atmosphere by the year 2100 (remember: your answer should be in unitsof gigatonnes of CO2)?2.B. For every 8 gigatonnes of CO2added to the atmosphere, the concentration of CO2rises by1 part per million (ppm). Based on your answer to Question 2.A., how much do you estimatethe concentration (in units of parts per million, ppm) will increase in the atmosphere between2019 and 2100, if we continue to emit carbon dioxide at the same rate we do now?2.C. Today, in 2019, atmospheric CO2levels are already near 412ppm. Now, add the numberyou calculated in Question 2.B. to that current level - what will be the concentration of CO2in the atmosphere (give your answer in unit of parts per million, ppm) if humans do continueto emit 40 gigatonnes of CO2every year for the next 80 years?Part 3: Carbon Dioxide and Energy3.A. On the next page is a simple graph (Figure 2) showing the relationship between theconcentration of CO2in the atmosphere (in units of parts per million, ppm) and the amount ofadditional energy trapped in the Earth system (in units of Watts per meter squared, Wm−2)by that CO2. Before humans started burning fossil fuels, the concentration of CO2in theatmosphere was approximately 280ppm. Based on your answer to Question 2.C. above andusing Figure 2 on the next page, approximately what will be the additional energy in the Earthsystem due to CO2emissions by 2100? Your answer will be in units of Watts per meter squared(Wm−2) In answering this question, consider 280ppm to be the pre-industrial (before humansstarted burning fossil fuels) baseline, and so measure the energy change (in units of Watts permeter squared) between 280ppm and the value you calculated in Question 2.C.1This section uses some approximations instead of the exact values3200 300 400 500 600 700 800 900 1000 1100012345678CO2 CONCENTRATION (PPM)ADDITIONAL ENERGY (Wm−2)Figure 2: The relationship between increases in carbon dioxide (CO2) concentrations (in unitsof parts per million, ppm) and the additional energy trapped in the Earth system (in units ofWatts per meter squared, Wm−2. Data are from Myhre et al. (1998)4Part 4: Carbon Dioxide, Energy, and Climate Change4.A. Scientists (including your instructors!) estimate that the average temperature of the Earthincreases by 0.75 degrees C for every additional Wm−2trapped in the Earth system by CO2.Based on this information and your answer to Question 3.A. above, what would you anticipatewould be the total increase in Earth’s temperature (your answers should be in degrees C) bythe year 2100 due to human emissions of carbon dioxide?4.B. Based on your knowledge and on Wednesday’s lecture, what are some of the major un-certainties related to how much Earth will warm by the end of this century due to CO2? Forinstance, so far your answers here assume that we will continue to emit the same amount ofCO2every year until 2100, but what other future scenarios (good or bad) are possible?ReferencesMyhre, G., E. J. Highwood, K. P. Shine, and F. Stordal (1998), New estimates of radiativeforcing due to well mixed greenhouse gases, Geophys. Res. Lett., 25 (14),


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