lab 7

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Georgia State University *

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1112

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Geography

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Oct 30, 2023

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docx

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Q1: What do scientists examine to determine temperatures (from stable isotopes) and greenhouse-gas concentrations over the past several hundred thousand years? Scientists use ice cores. They can also use isotopes of hydrogen and oxygen to show past temperatures. Q2: Are we currently in a glacial period or an interglacial period? How do you know? Interglacial period because of the current temperature. Q3: When did the most recent ‘maximum’ in a glacial period (which is really a temperature minimum or valley in the graph) occur? 15487 Q4: What is the approximate difference in temperature between a maximum in a glacial period (i.e. a valley) and a maximum in a preceding or succeeding interglacial period (i.e. a peak)? (Before moving onto Q6, consider this temperature difference – it should be surprising to you. Why?) The difference between them is -11. Q5: What is the approximate time interval between both maximums in glacial periods (i.e. the time between ‘valleys’ in temperature) maximums in interglacial periods (i.e. the time between ‘peaks’ in temperature)? 88746 Q6: Based on what you see happening as you move the time slider, what does ‘eccentricity’ mean? Eccentricity is the measurement of how circular an orbit is. Q7: What is the approximate length of the eccentricity cycle (i.e. how many years occur between periods of minimum eccentricity or how many years occurs between periods of maximum eccentricity)? The approximate length is 100,555 years

Q8: Based on the meaning for eccentricity you determined above, what does perihelion represent and what does aphelion represent? Perihelion represents the time that the earth is closest to the sun. Aphelion represents the time the earth is furthest from the sun Q9: In the present day, at what time of year do perihelion and aphelion occur? Perihelion happens on January 3 rd and aphelion happens on July 4 th . Q10: What is the approximate length of the tilt cycle (i.e. how many years elapse between periods of minimum tilt or how many years elapse between periods of maximum tilt)? The approximate length of the tilt cycle 40,000 years. Q11: Precession relates to a feature of the Earth’s tilt. What do you notice is happening to the Earth’s tilt when <Precession> is highlighted that could explain what this term means? [This NASA video may help also. Earth tilt is when precession is happening the change of the rotation of the earths axis. Q12: What is the approximate length of the precession cycle (i.e. how many years occur between periods of minimum precession or how many years elapse between periods of maximum precession?) The approximate length of the precession cycle is 26,000 years. Q13: Why did the high latitudes of the Northern Hemisphere receive such a small amount of insolation during the summers approximately 116,000 years ago? 116,000 years ago, the summer isolation dropped from 486.5 to 397.6 wm. Q14: How did Earth’s eccentricity change from 126,000 years ago to 116,000 years ago? Earths eccentricity increased.

Q15: How did Earth’s obliquity change from 126,000 years ago to 116,000 years ago? Earths obliquity decreased Q16: When did aphelion occur? You will probably need to slow down Earth’s orbit to read the words on the simulator. Aphelion occurs January 3 rd during the summer season. Q17: When did perihelion occur? You will probably need to slow down Earth’s orbit to read the words on the simulator. Perihelion occurs July 4 th during the winter season Q18: Considering changes in eccentricity, obliquity, and precession, why did the high latitudes of the Northern Hemisphere receive such a small amount of insolation during the summers approximately 116,000 years ago? High eccentricity and low Obliquity Q19: What is the relationship between temperature and CO 2 concentrations during glacial-interglacial cycles? Lower CO2 concentration during glacial cycles. During the interglacial cycles, CO2 is higher. Q20: What is the difference in CO 2 concentrations in parts per million (ppm) between maximums in interglacial periods (i.e. peaks in the graph) and maximums in glacial periods (i.e. valleys in the graph)? about 100 ppm Q21: Why do atmospheric CO 2 concentrations increase and decrease so much during glacial-interglacial cycles? Because CO2 is more soluble in the glacial cycle than interglacial cycles.

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Q22: Compared to the present-day global average temperature, how much lower was the global average temperature 21,000 years ago? 5.4 degrees celcius Q23: How much did CO 2 concentrations increase from 21,000 years ago to 1500 A.D? 95 ppm Q24: Why have CO 2 concentrations increased by at least another 100 ppm from 1500 A.D. to the present? Because of the burning of fossil fuels Q25: Why was the sea level so low? If the water wasn’t being stored in the oceans, where was it being stored? The water is in ice. Q26: The lower sea level also contributed to a higher albedo for Earth during the LGM (0.32) compared to today (0.30). How exactly does a decrease in sea level cause in an increase in albedo? Hint: Look at Florida and turn off and on the Last Glacial Maximum layer. It also wouldn’t hurt if you referred back to the LGM Albedo worksheet in the temperature model you examined in Lab 5 (Global Surface Temperature). Less water means higher albedo Why do glacial periods occur? A large tilt in Earth’s axis is coupled with the earth being farthest from the sun during the northern hemispheres summer. What happens when Earth transitions from a glacial period to an interglacial period? When the sea ice melts, the sea level increases. This means that the oceans absorb more CO2, which causes the oceans temperature to increase. This then causes more ice to melt.

How does an interglacial period differ from a glacial period? An interglacial period has higher temperatures. It also has higher CO2 concentrations, has a higher sea level, and there is less ice cover than during a glacial period.