CU1_HW_ANSWERS_Spring2022

1 Homework Questions for Climate and Us Week 1 Due the week of April 18 ANSWER KEY 1. Factors affecting Earth’s climate In lecture this week, Prof. McManus discusses the various factors that influence Earth’s climate. Consider what you learned in lecture to answer the following questions. A. Which of the following statements is/are true about Earth’s climate system? Select all that apply. a. Climate involves interactions with the ocean, the atmosphere, and the biosphere. b. El Niño-Southern Oscillation (ENSO) is an example of a climate phenomenon that has global impacts. c. Climate includes multiple factors, such as temperature and precipitation. d. Atmospheric circulation impacts Earth’s climate, but ocean circulation does not. a), b), and c) are correct answers. d) is incorrect because atmospheric AND oceanic circulation impact regional climate as both involve the redistribution of heat and energy across the globe. B. Which of the following statement(s) is/are true regarding factors that influence Earth’s temperature? Select all that apply. a. A higher number of sunspots decreases the amount of solar energy reaching the Earth’s surface, resulting in cooler temperatures. b. Large increases in albedo lead to warmer temperatures, as we have witnessed in recent decades. c. Greenhouse gases reflect incoming solar radiation, thus changing Earth’s temperature. d. Greenhouse gases absorb outgoing infrared radiation, thus changing Earth’s temperature. e. Greenhouse gases in the atmosphere increase the temperature of the Earth. d) and e) are the correct answers. a) is incorrect because a higher number of sunspots is a proxy for higher solar activity, which will lead to a greater amount of solar energy reaching the Earth’s surface and a small increase in temperatures on Earth . b) is incorrect because an increase in albedo would suggest more reflectance and cooler temperatures. c) is incorrect because greenhouse gases are transparent to incoming solar radiation, but absorb/re-emit outgoing infrared (longwave) radiation.

2 C. As you learned in lecture, the Earth currently has an albedo (or total reflectivity) of about 30%. Imagine a dystopian future where almost all of the glaciers and ice sheets on the planet have been replaced by dark, asphalt shopping mall parking lots. Assuming that only albedo changes and all of the other factors that influence climate on Earth remain constant, how would you expect Earth’s temperature to change relative to today? a. Temperature would be lower because Earth becomes more reflective. b. Temperature would be higher because Earth becomes less reflective. c. Temperature would be higher because Earth becomes more reflective. d. Temperature would be lower because Earth becomes less reflective. b) is the correct answer. The darker colored asphalt parking lots will result in less reflectivity at the Earth’s surface and therefore more absorption of radiation, increasing the temperature of the Earth. 2. Earth’s Energy Balance Any given planet’s climate is determined by an energy balance. Earth’s energy bal ance is such that it creates a livable environment for humans and other life, unlike those of nearby Venus or Mars. Climate forcings are factors that drive changes in climate and alter the Earth’s energy Balance. Use Figure 1 (below) to answer the following questions. Figure 1. Energy balance diagram showing the flow of energy (in Watts per square meter, or W/m 2 ) from the sun, Earth’s surface, and through the atmosphere. Yellow regions show incoming solar (shortwave) radiation. Red regions show outgoing infrared (longwave) radiation.

4 Figure 2. Measurements of atmospheric CO 2 concentration (red line) from the Mauna Loa Observatory station from 1958 to 2021 and seawater pH (blue line) from station ALOHA from 1990 to February 2021. Source: National Oceanic and Atmospheric Administration Pacific Marine Environmental Laboratory Carbon Program. A. The record of atmospheric CO 2 concentrations from Mauna Loa, Hawaii shows both a long-term trend from 1958-2021, as well as short-term (intra-annual) variability. Explain what causes intra-annual variability in atmospheric CO 2 in 1-2 sentences . Intra-annual variation in the record of atmospheric CO 2 corresponds to changes in the seasonal uptake of CO 2 by plants in the Northern Hemisphere. During spring/summer, plants take up CO 2 during photosynthesis and atmospheric CO 2 levels drop, reaching a minimum in early Fall. Conversely, during fall/winter, more CO 2 is being released to the atmosphere due to the decomposition of leaf litter/dead plant material, and atmospheric CO 2 concentrations reach a seasonal maximum in early spring. B. Estimate the annual rate of change for atmospheric CO 2 concentration (in ppm CO 2 per year) at the Mauna Loa Observatory station for the time period from 1994 to 2021. CO 2 in 1994 = roughly 360 ppm; CO 2 in 2021 = 416 ppm → 416 ppm – 360 ppm / 27 years = 2.1 ppm/year.

5 C. (i) As the concentration of CO 2 in the atmosphere increases, the concentration of CO 2 dissolved in seawater increases, causing a change in pH. Based on Figure 2, what can we conclude about the relationship between atmospheric CO 2 concentration and seawater acidity? Note that a decrease in pH means the water is becoming more acidic while an increase in pH means the water is becoming more basic. As atmospheric CO 2 increases, seawater pH decreases, meaning the seawater is becoming more acidic. C. (ii) The ocean is a ma jor carbon “sink” and currently absorbs about 26% of the CO 2 released by anthropogenic sources into the atmosphere (Le Quéré et al., 2016) 1 . This means the rate you calculated in question B(i) is actually only 74% of what it would be if the ocean wasn’t a ble to absorb atmospheric CO 2 . However, as seawater pH decreases (meaning water is more acidic), the ocean is able to absorb less CO 2 from the atmosphere. Based on your answer to B(i), what would the concentration of atmospheric CO 2 have been in 2021 if ocean absorption of atmospheric CO 2 all of a sudden went from 26% per year to 0% per year starting in 1994? Without the ocean able to act as a sink, the rate of CO2 increase in the atmosphere per year will increase to: 2.1/0.74 = 2.84 ppm per year. The concentration of atmospheric CO 2 in 1994 = roughly 360 ppm so we have: 360 ppm + 2.84 ppm per year (27 years) = 437 ppm. The concentration of CO 2 in the atmosphere would have been 437 ppm in 2021. D. Figure 3 (next page) shows the flux of carbon (in petagram C) per year measured at the Mauna Loa observatory in Hawaii (blue line) and in ice core bubbles from Antarctica (black line). The red line is the amount of carbon per year released by the burning of fossil fuels. (i) Based on Figure 3 (next page), what is the approximate difference between the flux of carbon released by fossil fuels and the flux of carbon measured at Mauna Loa in 2020? Give your answer in grams of carbon per day and write your answer in scientific notation (1 petagram = 1 x 10 15 grams). Flux measured at the Mauna Loa Observatory = 6.8 PgC/year Flux released by fossil fuels = 10 PgC/year Total approximate difference = 10 - 6.8 = 3.2 PgC/year 3.2 PgC/year * 1 x 10 15 g/PgC = 3.2 x 10 15 gC/year * 1 year/365 days = 8.77 x 10 12 gC/day 1 Quéré, C.L., Andrew, R.M., Canadell, J.G., Sitch, S., Korsbakken, J.I., Peters, G.P., Manning, A.C., Boden, T.A., Tans, P.P., Houghton, R.A. and Keeling, R.F., 2016. Global carbon budget 2016. Earth System Science Data , 8 (2), pp.605-649.

7 Figure 4. Average monthly δ 13 C records of atmospheric CO 2 from Mauna Loa Observatory, Hawaii (black dots/curve) and South Pole, Antarctica (red dots/curve) from 1975 to 2022. (N ote: δ 13 C represents the ratio of 13 C/ 12 C relative to a standard). Source: Scripps CO 2 program. (i) Changes in δ 13 C represent the ratio of 13 C/ 12 C relative to a standard, so a higher δ 13 C corresponds to a higher 13 C/ 12 C ratio and a lower δ 13 C corresponds to a lower 13 C/ 12 C ratio. Using the data shown in Figure 4 (above) , calculate the average rate of change of δ 13 C (in per mil per year) from 1980 - 2022 at the South Pole, Antarctica (red dots/curve in Figure 4). 1980 δ 13 C = about -7.6 per mil 2022 δ 13 C = about -8.5 per mil Total years = 42, so: (-8.5 - - 7.6) per mil/42 years = -0.9 per mil/42 years = -0.02 per mil per year (ii) Which location shows greater intra-annual variability in δ 13 C value of atmospheric carbon dioxide: the South Pole, Antarctica or Mauna Loa, Hawaii? Speculate as to what may be responsible for this difference. The δ 13 C values of atmospheric carbon dioxide measured at the Mauna Loa, Hawaii site shows more intra-annual variability than the values for carbon dioxide measured at the South Pole. This is because the intake of carbon dioxide by plants in the spring and summer vs. release in fall and winter is more dramatic in the Northern Hemisphere, due to larger land masses and prevalence of seasonal vegetation. Plants preferentially take in the 12 C isotope of carbon more in the spring and summer, increasing the δ 13 C value of the carbon dioxide left in the atmosphere at this time.

8 (iii) For each of the following sentences (a - e), select the corresponding word choice that most accurately completes the sentence. a.) If we continue to increase our use of fossil fuels, the 13 C/ 12 C ratio of carbon dioxide in the atmosphere will INCREASE/ DECREASE /STAY THE SAME. b.) If we continue to increase our use of fossil fuels, the δ 13 C value of carbon dioxide in the atmosphere will INCREASE/ DECREASE /STAY THE SAME c.) Burning of fossil fuels is a carbon SOURCE /SINK. d.) The absorption of CO 2 into ocean water is a carbon SOURCE/ SINK e.) If we stop using fossil fuels, the concentration of CO 2 in the atmosphere would eventually INCREASE/ DECREASE /STAY THE SAME.