Quiz2_practice_2023t1_solutions

EOSC 340 Quiz 2 practice problems 2022t1 1 /12 This quiz will cover all topics from day 9 (climate feedbacks and sensitivity) through day 19 (Modern Carbon cycle), including material covered in assignments 3, 4 and 5. To help you do well on the quiz, work through these practice problems, look over the worksheets and the solutions, and go through the class slides. Think about how similar questions could be made, and try to answer those too. 1. Ice-albedo feedback can be written: ࠵? = # ࠵?࠵? ࠵?ice area , × # ࠵?ice area ࠵?࠵? , Which of the following statements is correct? A) / 01 0ice area 2 is positive, / 0ice area 03 2 is positive, ࠵? is positive B) / 01 0ice area 2 is positive, / 0ice area 03 2 is negative, ࠵? is negative C) / 01 0ice area 2 is negative, / 0ice area 03 2 is positive, ࠵? is negative D) / 01 0ice area 2 is negative, / 0ice area 03 2 is negative, ࠵? is positive E) / 01 0ice area 2 is negative, / 0ice area 03 2 is negative, ࠵? is negative Remember that a positive increase in ice area is cooling, and that ice area decreases with a positive temperature change. 2. If the change in radiative forcing per square kilometer of arctic ice ( ! R / ! (ice area) ) is -10 -6 (W m -2 ) / km 2 , how much ice would have to melt per degree of warming ( ! (ice area)/ ! T ) to make the ice- albedo feedback strength c A = 0.25 W m -2 K -1 ? A) -0.25 x 10 6 km 2 / K B) -0.5 x 10 6 km 2 / K C) 1.5 x 10 6 km 2 / K D) 2.0 x 10 6 km 2 / K E) 2.5 x 10 6 km 2 / K 3. Suppose we know that the climate sensitivity " = 0.8 K / (W m -2 ). Further suppose that as the climate warms all the Arctic ice melts, preventing the ice-albedo feedback (f A = 0.30 W m -2 K -1 ) from operating. At the same time, a new methane-permafrost feedback starts (f M = 0.2 W m -2 K -1 ). What is the resulting climate sensitivity? A) 0.2 K / (W m -2 ) B) 0.34 K / (W m -2 ) C) 0.74 K / (W m -2 ) D) 1.25 K / (W m -2 ) E) 3.2 K / (W m -2 ) Use ࠵? = − 6 7 = −1 / ∑ ࠵? ; = in two steps, first find the total current feedback f c = -1/0.8 = -1.25 then subtract the old ice feedback, add the new methane feedback and turn it back into λ: ࠵? = -1/(-1.25 -0.3 + 0.2) = 0.74

EOSC 340 Quiz 2 practice problems 2022t1 2 /12 4. A black cloud layer at a height of 10 km is radiating 160 Wm -2 . Given an atmospheric lapse rate of -7 K/km, what is the best estimate for the temperature below the cloud at the Earth's surface? A) 290.5 K B) 295.5 K C) 300.5 K D) 305.5 K E) 310.5 K Two steps: 1. use equation to get the cloud temperature: (160./sigma)**0.25 = 230.48052309462736 2. Following the temperature profile down 10 km to the surface adds 70 degrees to give 300.5 K 5. According to the IPCC, the net radiative forcing by humans is currently between 1 and 2 Wm -2 above the pre-industrial value. If the climate sensitivity is 2.5 K/CO 2 doubling, what is the range of the equilibrium temperature increase between preindustrial times and today? A) between 0.42 K and 1.3 K B) between 0.44 K and 2.5 K C) between 0.65 K and 1.3 K D) between 1.36 K and 5 K E) between 2.45 K and 5 K 1 doubling is 3.8 Wm -2 = sensitivity = 2.5/3.8 = 0.66 K/(Wm -2 ) which is also the temperature change for 1 Wm -2 forcing. For 2 Wm -2 : 0.66*2 = 1.32 6. According to the IPCC, the magnitude of which of these climate feedback processes is the most uncertain? A) Planck feedback B) ice-albedo feedback C) lapse rate feedback D) cloud radiative feedback E) water vapour feedback 7. Let # s say we # re aiming to stabilize global temperature at 4 K above pre-industrial values. How many TOTAL Gtonnes of C can we emit if we are to achieve this goal, starting the count at the beginning of the industrial revolution? Assumptions to use: (1) assume climate sensitivity of 1 K (W m -2 ) -1 , (2) assume pre-industrial atmospheric CO 2 is 270 ppm, (3) assume 50% of what # s emitted stays in the atmosphere on the time scale of interest. A) about 300 Gtonnes carbon B) about 600 Gtonnes carbon C) about 1200 Gtonnes carbon D) about 2400 Gtonnes carbon E) about 4800 Gtonnes carbon Step 1, use Error! Reference source not found. to get the new CO 2 mixing ratio: np.exp(4/3.8*np.log(2))*270 = 560.06 Step 2: convert that to Gtonnes carbon assuming that half stays in the atmosphere: I = εσ T 4 Δ F = 3.8W m -2 ( ) ln newpCO2 / origpCO2 ( ) ln 2 ( )

EOSC 340 Quiz 2 practice problems 2022t1 4 /12 Note: it is true that local evaporation will have less O18 at colder temperatures, but this is not the MAIN cause of the relationship shown in the graph – assignment 4 takes you through why B is the correct answer B. Most water vapour is evaporated in the tropics. As the water vapour moves towards the poles, temperatures decrease, more and more water vapour condenses and falls as precipitation – because 18O is preferentially condensed, this causes the remaining water vapour to get lighter as the air travels further into colder regions, and thus precipitation also gets lighter. C. Most water vapour is evaporated in the tropics. As the water vapour moves towards the poles, temperatures decrease, more and more water vapour condenses and falls as precipitation – because 18O is preferentially condensed, this causes the remaining water vapour to get lighter as the air travels further into colder regions, and thus precipitation also gets lighter. D. Most water vapour is evaporated in the tropics. O16 is preferentially condensed and precipitated out, leaving more O18 by the time the water vapour reaches the poles. E. All water vapour has the same ࠵? 18O, but at colder temperatures more of the O16 condenses and is precipitated out, leading to more negative ࠵? 18O in the precipitation. 11. You measure a value of ࠵? 18O in an ice core of -20 % . Use the graph below to determine the residual vapour fraction of the air this precipitation came from: A. 0.01 B. 0.19 C. 0.4 - Remember that the ice core is recording the precipitation (rain/snow), not the water vapour itself. D. 0.8 12. Which of the following statements are accurate about paleoclimate data? i) Values of ࠵? 18O from ice cores give us very accurate estimates of average global temperatures by themselves - Not accurate – remember that the ࠵? 18O signal in ice cores can be complicated by changes in height of the ice sheet, changes in the seasonality of when the precipitation was mostly falling. ii) We use ice sheet borehole temperatures in combination with ࠵? 18O values of ice to get accurate temperatures

EOSC 340 Quiz 2 practice problems 2022t1 5 /12 - True iii) ࠵? 18O values from benthic shells in ocean sediment cores tell us there were large changes in temperature in the tropics between glacial and interglacial times. - Not true – the tropics changed temperature relatively little between glacial and interglacial times iv) ࠵? 18O values from benthic shells in ocean sediment cores tell us mostly about how much ice was stored on land, and therefore about global sea levels - True A. All are true/accurate B. i, iii, iv are true/accurate C. ii and iii are true/accurate D. ii and iv are true/accurate E. None are true/accurate 13. Below is a plot of ࠵? 18O measured in the shells of benthic foraminifera plotted against age in a sediment core. What is the BEST statement about climate conditions at the time that the arrow is pointing to, compared to the rest of the data shown here? A. Relatively warm; relatively high sea level B. Relatively warm; relatively low sea level C. Relatively cold; can’t tell about sea level D. Relatively warm; can’t tell about sea level - The information is telling us about how much of the 16O is locked away in the ice sheets. When 18O of the water is lower (as in the point with the arrow), this means there is more 16O in the ocean water, which means less is locked in ice sheets, so there is less ice sheet, and therefore higher sea levels. E. Relatively cold; relatively high sea level F. Relatively cold; relatively low sea level - Be careful with the y axis: lower values are higher up (this is because these types of graphs are often created with global temperatures in mind – so as you go up the y axis, global temperatures increase).

EOSC 340 Quiz 2 practice problems 2022t1 7 /12 A. 0 - 8°C B. 8-16°C C. 12 - 22°C D. 22 - 25°C - whilst Globigerina bulloides can live at this temperature range, the maximum percentage shown in the graph from temperatures above 22C is 30%, so it would be hard to find 50% for this temperature range. E. 22 - 27°C a. Globigerina bulloides b. Globigerinoides ruber c. N. pachyderma The distribution of forams as a % of the total foraminifer population based on the temperature of surface waters (x axis) obtained by satellite data. The black and white circles represent data collected from two different marine sediment cores in different locations. a. Globigerina bulloides, b. Globigerinoides ruber and c. N. pachyderma 17. Imagine you are evaluating a sediment core, which contains a record of the microfossils recovered at one geographic location, through time. You generate the following data: - At 400 cm depth in the core, you find only N. pachyderma and no Globigerina bulloides - At 300 cm depth in the core, you find only Globigerina bulloides and no N. pachyderma Over the time period (unknown) spanned by these two data points, what is the best interpretation about what happened at this location? Use the information in the figures above. Be sure to think about which way “time” runs in a sediment core. A. The surface ocean temperature at this location was colder than 8 ° C, then warmed up to temperatures warmer than 10 ° C. B. The surface ocean temperature at this location was warmer than 10 ° C, then cooled off to temperatures colder than 8 ° C. C. The surface ocean temperature at this location probably didn # t change over this time period, but the foraminifera migrated.

EOSC 340 Quiz 2 practice problems 2022t1 8 /12 D. The surface ocean temperature got colder over time, but we can # t say anything about temperature values. E. The surface ocean temperature got warmer over time, but we can # t say anything about temperature values. Deeper values are older, so further back in the past (400m depth) only N. pachyderma were living in the region and based on the graphs in question 8, they only live in surface water cooler than 8C. Then, more recently (300m depth), only Globigerina bulloides were living, and they only live in temperatures above 10C, so the ocean temperatures must have warmed. 18. Which statement most accurately describe the relationship between orbital (Milankovitch) cycles and Earth # s climate changes over the past few million years? Choose the BEST answer. A) Changes in eccentricity change the solar constant enough to account for Earth being 5- 6°C colder during ice ages (compared to today). B) Changes in tilt change the solar constant enough to account for Earth being 5-6°C colder during ice ages (compared to today). C) Changes in precession change the solar constant enough to account for Earth being 5- 6°C colder during ice ages (compared to today). D) Certain combinations of changes in tilt and precession change the solar constant enough to account for Earth being 5-6°C colder during ice ages (compared to today) from forcing alone. E) Changes in Earth’s orbital parameters don’t change the solar constant enough to account for Earth being 5-6°C colder during ice ages (compared to today) from forcing alone. The forcing does not match the temperature change – so feedback is required. See the second part of the in- class worksheet on Milankovitch cycles. 19. Humans are adding a spike of CO 2 to the atmosphere over a fairly short period of time, by releasing carbon from the fossil fuel reservoir and adding it to the atmosphere. Eventually, this carbon will be taken out of the atmosphere again. Which of the following lists processes that will remove this excess carbon from the atmosphere, IN ORDER FROM SHORTEST TO LONGEST TIME SCALE ? A) uptake by photosynthesis, dissolution into ocean water; reaction with silicate rocks B) dissolution into ocean water; reaction with silicate rocks; uptake by photosynthesis C) reaction with silicate rocks; uptake by photosynthesis; dissolution into ocean water D) reaction with silicate rocks; dissolution into ocean water; uptake by photosynthesis E) uptake by photosynthesis; reaction with silicate rocks; dissolution into ocean water A. Uptake by photosynthesis is shortestOcean uptake is shortest (years to 100s of years); reaction with silicate rocks is longest (100,000s to millions of years) 20. The figure at right represents the variation in atmospheric CO 2 at one location in the NORTHERN Hemisphere over the time period of one year. In which months do points & A ’ and & B ’ most likely occur? Choose the BEST answer.

EOSC 340 Quiz 2 practice problems 2022t1 10 /12 Where A is the fraction of maple syrup, B is the fraction of cane sugar, and so A+B = 1 -24.3A + -11.8(1-A) = -21.8 (-24.3 + 11.8)A $ 11.8 = -21.8 -12.1A = -21.8 + 11.8 = -10 A = -10/-12.1 = 0.82 So your syrup is likely to be about 80% maple syrup, 20% cane sugar, 24. Using the numbers in the figure below, calculate approximately what percentage of human carbon emissions are taken out of the atmosphere every year by the ocean alone . A) About 0.2% B) About 9% C) About 19% D) About 55% E) About 81% Total into ocean: 92.2 – 90.5 = 1.7 1.7/9 = 0.19 = 19% 25. Say that about 50% of CO 2 released to the atmosphere stays there for the long-term, and the rest gets taken up fairly quickly by the ocean and land biosphere/soils. How much CARBON (in Gtons) would have to be added to the atmosphere in order to increase atmospheric CO2 by 50 ppm? A) about 13 Gtons B) about 105 Gtons C) about 210 Gtons D) about 560 Gtons E) about 840 Gtons 2.1 GtonC ~ 1ppm so 50ppm ~ 105 Gtons stays in the atmosphere. But this is only 55% of what it released, so total released = 105 * 2 = 210 Gtons 26. Which of the statements about the figure below are not consistent with the figure? A) Sea level is rising during interval A B) Oceans are warming during interval C C) The rate of outgassing exceeds the rate of weathering during interval C D) Greenhouse gas concentrations are falling during interval A E) Ocean temperatures begin to cool during interval B

EOSC 340 Quiz 2 practice problems 2022t1 11 /12 Increasing benthic d 18 O means dropping temperature (more land) ice = lower sea level. All other statements are consistent. The following questions are open-ended to help you study; but on the exam all questions will be multiple choice. 27. The rate that methane is removed from the atmosphere is proportional to the methane concentration [CH 4 ], with a 10 year half life, i.e. the sink of methane is I out = [CH 4 ] ln(2)/10 ppb/year (parts per billion per year). If the total emission rate of Methane from all sources is I in = 125 ppb/year what is the equilibrium atmospheric concentration of methane? In equilibrium, I in = I out. So [CH4] ln(2)/10 = 125 [CH 4 ] = 125 * 10 / ln(2) = 1803 ppb 28. Draw a feedback loop involving ice that helps explain the mismatch between the amplitude of insolation forcing on Milankovitch time scales (relatively small) and the climate response (relatively large). ↑ Solar -> ↑ temperature -> ↓ ice coverage -> ↑ solar absorption -> ↑ temperature Must be an amplifying feedback to explain the mismatch 29. Draw a feedback loop involving carbon that helps explain the mismatch between the amplitude of insolation forcing on Milankovitch time scales (relatively small) and the climate response (relatively large). ↑ Solar -> ↑ ocean temperature -> ↓ CO 2 solubility -> ↑ atmospheric CO 2 -> ↑ greenhouse -> ↑ ocean temperature Must be an amplifying feedback to explain the mismatch 30. Describe how the silicate weathering thermostat works. On very long time scales, what generally happens to the greenhouse effect as solar radiation changes? ↑ Solar -> ↑ temperature weathering rates -> ↓ atmospheric CO 2 -> ↓ greenhouse -> ↓ temperature This feedback acts to stabilize temperatures, reducing the greenhouse effect as solar forcing increases, thereby keeping temperatures more constant