Unit 2: Earth's Atmosphere and Its Influence on Temperature
By the end of the unit, students will be able to:
- Determine which wavelengths of incoming solar and outgoing terrestrial radiation are being absorbed by the atmosphere by examining radiation spectra.
- Describe how greenhouse gases elevate surface temperatures above the expected effective temperature.
- Analyze timeseries data of atmospheric CO2 to determine current growth rate and how the growth rate has changed since measurements began.
- Describe how changes in society have changed atmospheric CO2.
- Calculate individual contributions to anthropogenic CO2 emissions.
Context for Use
This unit is designed for a 50-minute class period and incorporates both interactive lecture and activity components. It assumes that students have covered the material from Unit 1 and have completed the homework assignment from that unit. Question 5 from the Unit 1 homework asks the students to calculate the effective temperature of Earth, and their answers are used as the jumping-off point for this unit. After the class period, students have followup homework questions on the material.
If Unit 1 is not presented prior to this unit, students should be familiarized with the concepts of electromagnetic and blackbody radiation in order to prepare for the concepts in this unit.
Description and Teaching Materials
Unit 2 is split into two equal-length parts. The homework for Unit 1 includes having the students calculate Earth's effective temperature, so they should be prepared with this information prior to the start of class.
Part 1 (25 minutes) is a guided lecture and discussion of the role the atmosphere plays in altering the spectra of incoming (from the sun) and outgoing (from Earth) radiation. This is conducted with a PowerPoint containing relevant images. Three images are used as focal points for think-pair-share reflections, with guidance in the Notes section of the Unit 2 PowerPoint (PowerPoint 2007 (.pptx) 4.5MB Nov14 16).
- What do we know about the Sun's outgoing radiation spectrum?
- How does the energy received at Earth's surface differ from what we'd expect from an ideal blackbody?
- How does Earth's outgoing radiation, viewed from space, differ from what is expected?
After investigation of these spectra, students will see how the greenhouse effect prevents energy from leaving the earth system, producing the observed surface temperature in excess of what they calculated (Earth's effective temperature, 255 K) for the beginning of class.
Part 2 (25 min) has students use real data regarding the changing concentration of CO2, a greenhouse gas, in the atmosphere.
- Unit 2 Activity (Word) (Microsoft Word 2007 (.docx) 67kB Jul31 17) or PDF (Acrobat (PDF) 153kB Nov14 16)
In small groups in class, they investigate the following questions:
- How has the growth rate of CO2in the atmosphere changed since measurements began in 1958?
- What are the societal forces driving these changes in atmospheric CO2?
- Why does atmospheric CO2have an annual "zig-zag" pattern?
The questions in the homework (Unit 2: Homework (Word) (Microsoft Word 2007 (.docx) 132kB Nov14 16) or PDF (Acrobat (PDF) 152kB Nov14 16)) on the handout are designed to be completed at home and assessed later by the instructor. These questions have students predict future CO2 concentrations, calculate their carbon footprint, and make predictions regarding feedbacks in the Earth system.
Teaching Notes and Tips
The lead-in to this unit refers to a question posed as homework at the end of Unit 1, where students are asked to calculate Earth's effective temperature in K, °C, and °F. If Unit 2 is being used in stand-alone fashion, this opening section will need to be adjusted.
There are many pause points within the PowerPoint that are designed for students to think-pair-share. The instructor should allow the students a minute or two to discuss the question with a neighbor, then solicit responses from the class. This provides a way to promote interaction, even in larger classroom settings.
The instructor may recognize the concept sketch think-pair-share exercise from the student pre- and post-module survey Concept Sketch Pre and Post Survey (Word) (Microsoft Word 2007 (.docx) 23kB Nov18 16) or PDF (Acrobat (PDF) 42kB Nov18 16) first mentioned in Unit 1. After discussing the sketch, it is worth asking students to reflect on how their knowledge of the system of Earth's energy balance has developed since the beginning of the module.
The CO2 data from Mauna Loa are continually updated; the instructor may wish to find the most current image at: http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo_full.
If the instructor is using the module in 75-minute class blocks, Part 1 of this unit can easily be appended to Unit 1. Then Part 2 of this unit can be used to lead in to the activities in Unit 3.
- Guided think-pair-share activities within PowerPoint assess learning goal 1
- Guided think-pair-share activities in PowerPoint, including concept sketch, assess learning goal 2
- In-class activity assesses learning goals 3 and 4
- Homework assignment assesses learning goal 5
Formal, individual assessment can be done through the homework questions.
Exam questions tied to the unit's learning goals can be found here:
Instructors may use the pre/post survey in class or as a take-home assessment tool:
- Concept Sketch Pre and Post Survey (Word) (Microsoft Word 2007 (.docx) 23kB Nov18 16) / PDF (Acrobat (PDF) 42kB Nov18 16)
References and Resources
- NASA video on Earth's energy balance: http://www.youtube.com/watch?v=DOAqECd70Ww
- NASA video on the greenhouse effect: http://www.youtube.com/watch?v=ZzCA60WnoMk
- NASA video on human activities and CO2: https://www.youtube.com/watch?v=3IDBMsdS3lI