Viewer’s Guide and Discussion Questions:
Taking Earth’s Temperature: Delving into Climate’s Past
Summary
This list of questions follows the main topics as they are presented in the documentary. They can be used as a springboard to class discussions, or to create a worksheet for students to reflect on while watching the documentary. The film is 55 minutes long.
Grade level: High school and early college
Topics: Past climate changes; proxy records; climate forcing
Climate Literacy Benchmark: Principle 4d, “Scientific observations indicate that global climate has changed in the past, is changing now, and will change in the future. The magnitude and direction of this change is not the same at all locations on Earth.”
Student questions
1. Reflect on how the movie differentiates between climate and weather. What is the key difference?
2. Why is it important to study past climate (paleoclimate)?
3. What is a proxy climate record?
4. The scientists are collecting a sediment core from the bottom of an Arctic lake. What information about past environmental changes might this core contain?
5. Why do the researchers use sediment traps?
6. Why is fieldwork important?
7. Why is volcanic ash an important marker for lake sediment and other geological archives?
8. What is paleoecology?
9. How is pollen used in paleoecology?
10. How are corals used to infer past climate?
11. How are tree rings used as proxy climate indicators?
12. Why are speleothems from caves a valuable climate proxy?
13. In addition to natural sources of information, scientists also study historical documents that attest to past climate. What are some historical archives mentioned in the film?
14. What are some advantages of “multi” proxy records?
15. Why is it important to get a grasp on regional climate variations, not just global temperature changes?
16. Climate forcings are physical factors that cause climate to change. Give some examples of climate forcings. Which forcings occur over shorter time scales and which occur over longer time periods?
17. Is the carbon dioxide emitted from natural sources different from that emitted by human sources in terms of its role in the greenhouse effect?
18. How have CO2 and temperature changed in past and what is the source of this information?
19. What is a climate model? What general information goes into a climate model?
20. How do paleoclimatologists and climate modelers work together to improve climate models?
Questions with answers
1. Reflect on how the movie differentiates between climate and weather. What is the key difference?
Weather changes daily and year-to-year. Climate involves underlying trends that occur over many decades.
2. Why is it important to study past climate (paleoclimate)?
Observations of climate are too short to capture the full range of natural variability, especially those that operate on timescales of many decades to centuries. Past climate can give insights into possible futures. Future climate will be determined by both natural and human causes.
3. What is a proxy climate record?
A proxy is a stand-in or substitute for the actual measurement. Proxy climate records are biological, geological, and chemical evidence from past eras that can be related to the temperature or other aspects of climate of that time.
4. The scientists are collecting a sediment core from the bottom of an Arctic lake. What information about past environmental changes might this core contain?
(a) The amount of meltwater generated by the glaciers influences the amount of sediment that ends up in the lake. Higher summer temperatures can lead to more glacier melt and more sediment accumulation at the lake bottom. (b) The amount of organic matter deposited in the lake reflects the amount of vegetation that grows in and around the lake. The longer the growing season, the more vegetation (production of organic mater) represented in the lake sediment.
5. Why do the researchers use sediment traps?
They can learn about what controls the amount of sediment that settles to the bottom of the lake at different times of the year. This gives them more information about how the layers in the sediment core relate to rainfall or snowmelt runoff, or glacier meltwater, all of which can carry sediment to the lake.
6. Why is fieldwork important?
To accurately interpret the information contained in the geological record, scientists need to witness the natural processes that occur in the field.
7. Why is volcanic ash an important marker for lake sediment and other geological archives?
Volcanic ash layers are deposited in discrete events and serve as a precise time-marker. They can be compared with ash layers from other sites to correlate and improve comparisons among them. Large volcanic events inject aerosols high into the atmosphere that may cause temporary cooling. So volcanoes are a form of climate forcing.
8. What is paleoecology?
Paleoecology is the study of how past ecosystems in an area changed over time. Fossil organisms, or their parts, that are used in paleoecology include pollen, beetle carapaces, and bits of vegetation or charcoal.
9. How is pollen used in paleoecology?
Pollen is deposited along with the sediment that accumulates at the bottom of lakes. The size and shape of pollen grains are unique to a plant species. Some plants live in colder environments, some in warmer and wetter, etc. Therefore, information about past environments and climate can be deduced from the composition of plant species living in an area through time.
10. How are corals used to infer climate?
Much like tree rings, corals grow an annual band of calcium carbonate (CaCO3) to their skeleton. The thickness of the band, and the chemical signatures left in the band, can be interpreted as changes in temperature, rainfall and nutrients entering the ocean.
11. How are tree rings used as proxy climate indicators?
For trees whose rate of growth depends on temperature, such as those near tree line, the thickness of each annual layer is proportional to the site temperature.
12. Why are speleothems from caves a valuable climate proxy?
The temperature in a cave closely matches the mean annual temperature at the site. Some speleothems are made up of annual bands of calcite and thereby provide a timeline for the proxy record. The thickness of the band, and the chemical signatures left in the band, can be interpreted as changes in rainfall and temperature.
13. In addition to natural sources of information, scientists also study historical documents that attest to past climate. What are some historical archives mentioned in the film?
Ship logs. Drawings and paintings of glacier extent. Journal entries (not mentioned in film).
14. What are some advantages of “multi” proxy records?
Different proxies can be compared to determine if they are yielding similar (reinforcing) or different climate information. Some proxies are better at sensing some aspects of climate, like temperature, whereas others are better recorders of different climate variables. Some proxies are available in some areas but not in others. By combining information from multiple proxies, scientists can gain wider geographic coverage.
15. Why is it important to get a grasp on regional climate variations, not just global temperature changes?
Global changes are felt differently from place to place. As the ocean and atmosphere redistribute heat and moisture, some places cool while others warm. Climate changes at a regional scale are generally more relevant to ecosystems and societies.
16. Climate forcings are physical factors that cause climate to change. Give some examples of climate forcings. Which forcings occur over shorter time scales and which occur over longer time periods?
Large volcanic eruptions cause cooling over years. The output of the sun can vary on timescales of decades to millennia. Orbital cycles cause very slow (thousands of years) changes of the amount of sunlight received at different latitudes during different seasons. The concentration of greenhouse gasses control the amount of infrared (heat) energy that is absorbed and reradiated by the atmosphere, and can change over all time scales.
17. Is the carbon dioxide emitted from natural sources different from that emitted by human sources in terms of its role in the greenhouse effect?
No. The influence of human-generated CO2 is the same as natural sources. However (not covered in the movie), the CO2 generated by burning fossil fuel can be recognized by it isotopic composition.
18. How have CO2 and temperature changed in past and what is the source of this information?
Ancient atmosphere trapped in bubbles within glacier ice as been analyzed to determine the level of CO2 over the past hundreds of thousands of years. They show that temperature and CO2 content are closely related (higher temperatures occur when CO2 levels are higher).
19. What is a climate model? What general information goes into a climate model?
Climate models are analytical tools for studying the climate system. They use mathematical equations that govern the movement of mass and energy around the globe. This enables them to simulate the interactions among the components of the climate system, including the atmosphere, oceans, ice sheets and biosphere. Their output is displayed as a map, as changes in temperature and other aspects of climate through time and through space.
20. How do paleoclimatologists and climate modelers work together to improve climate models?
Past climate changes provide challenging targets for climate models. Climate models have been programed to include changes in the amount of solar and volcanic forcing of the past. If the models can correctly simulate the conditions that the geological evidence shows occurred, then they are more likely to accurately predict future changes. Mismatches between the proxy data and the climate-model simulations could also point to misinterpretations of the proxy records.
1