Unit 2: Climate Forcings
At the conclusion of this unit, students will be able to:
- Utilize systems thinking to examine how emissions and feedbacks within the climate system influence global equilibrium temperature.
Context for Use
Like Unit 1, this unit is suitable for any level of undergraduate class and is primarily directed at non-climate science courses. Upper division geoscience courses, such classes as meteorology, oceanography, or climatology, may not need to include this unit before using later units in the module as the material covered here would likely be covered in more detail prior to the start of the module or known to students in upper division courses. For introductory courses, this unit is flexible enough to be taught as a stand-alone introduction to the greenhouse effects and modeling climate change.
This unit was designed to be carried out over one long class period (about 75 minutes) and it takes every minute of that. It would also work well (perhaps better, if you can, to take your time) in two 50-minute class periods.
Description and Teaching Materials
Teaching Materials Required for Unit 2
- Computer with a connection to a projector and the Internet to show the Unit 2 PowerPoint (PowerPoint 2007 (.pptx) 50.1MB Nov7 16) with the aid of the Unit 2 Lecture Notes (Microsoft Word 2007 (.docx) 255kB Nov7 16).
- Two mason jars with a ~1/4" hole in each lid, two identical lights, two identical thermometers, black and white construction paper, and an optional video camera for use in larger classrooms to conduct this Demonstration (Microsoft Word 2007 (.docx) 411kB Nov7 16).
Prior to class session
Demonstration sheet (Microsoft Word 2007 (.docx) 411kB Nov7 16).
Students should watch and listen to this animated PowerPoint (MP4 Video 147.6MB Oct26 16) lecture (~20 minutes). Main concepts covered in this animated PowerPoint are:
- Greenhouse Gas (GHG) concentrations and temperature both go up and down together.
- We can use the concept of equilibrium to understand how the greenhouse effect warms our planet (i.e., why and how the planet is constantly striving to achieve an "equilibrium temperature").
- There are a variety of ways in which the planet's equilibrium temperature can vary. Most important for today and the next few weeks is the impact of carbon emissions.
- Introduce the concept of a model by drawing an analogy with the "equilibrium 1-layer model" to explain the greenhouse effect.
Homework: At the end of the animated lecture students are asked to answer two questions posed on the last slide of the animated PowerPoint:
- What is another way that we could improve this simple model?
- List 3 things that can modify the temperature of the planet. Of these three which (if any) are caused by humans?
We suggest collecting written responses to ensure students have watched the animated PowerPoint and are prepared for the discussion and activities in class and returning them at the start of Unit 3 (grading not necessary).
During class (2 Parts, total time: 75 minutes)
Part 1. Forcings, feedbacks, and equilibrium (40-45 minute demonstration & discussion):
Begin the class demonstration by turning the lights on the black and white mason jars set up by following Demonstration sheet (Microsoft Word 2007 (.docx) 411kB Nov7 16). Use this demonstration to:
- Define the concept of a forcing and explain that carbon dioxide is a forcing in our current climate system.
- Define the concept of a feedback by considering the thought question: what if the white paper turned to a darker color as it got hotter?
- Show that, though the black jar is hotter, both jars don't heat indefinitely. They eventually reach equilibrium.
While the jars heat, show the Unit 2 PowerPoint (PowerPoint 2007 (.pptx) 50.1MB Nov7 16) with the aid of Unit 2 Lecture Notes (Microsoft Word 2007 (.docx) 255kB Nov7 16) to formalize the concepts of feedbacks and systems thinking.
Be sure to:
- Show your students how to draw a feedback loop (this skill is required in the feedbacks activity coming up next).
- Introduce the concept of equilibrium climate sensitivity, which will be needed in later units, and make the connection that a positive feedback does not lead to indefinite warming.
- Discuss uncertainty. Uncertainty doesn't mean that we know nothing! It means that there are a range of answers that are possible based on the best available evidence.
- Reinforce the concept that feedbacks are intimately related to systems thinking - different aspects of the climate system all interact together to result in climate change.
Part 2. Understanding Feedbacks Using Systems Thinking (30-35 minute small group activity): This think-pair-share activity encourages a deeper understanding of forcings and feedbacks. Questions build from low level memorization questions to higher level questions that ask the student to apply, analyze, and create their own feedbacks. Distribute hardcopies or direct students to the Feedbacks Activity sheet (Microsoft Word 2007 (.docx) 103kB Nov7 16) (and Feedbacks Rubric (Excel 2007 (.xlsx) 52kB Nov7 16) if you are going to grade their answers). The activity and rubric are also available for download on the Students Material page. The Feedbacks activity is best done in groups of 2-3 and would also be suitable as homework assignment if there is not sufficient class time.
With 5-10 minutes remaining, conclude class by reminding students that climate feedbacks collectively determine the equilibrium climate sensitivity---the amount of warming that results from doubling the atmospheric CO2 concentration, which is reported as a range due to uncertainty in the strength of feedbacks. In the next class, they will use a model to examine, among other things, the effects of climate sensitivity of climate change predictions.
Teaching Notes and Tips
- Animated PowerPoint to view before class (MP4 Video 147.6MB Oct26 16)
- Demonstration Instructor sheet (Microsoft Word 2007 (.docx) 411kB Nov7 16)
- Unit 2 PowerPoint (PowerPoint 2007 (.pptx) 50.1MB Nov7 16)
- Unit 2 Lecture Notes (Microsoft Word 2007 (.docx) 255kB Nov7 16)
- Feedbacks In-Class Activity (Microsoft Word 2007 (.docx) 103kB Nov7 16), Feedbacks Grading Rubric (Excel 2007 (.xlsx) 52kB Nov7 16), and
- A Sample Concept Map (Acrobat (PDF) 6.7MB Aug4 16) showing what we've discussed so far, and the Module System Diagram that we will add to in subsequent units.
References and Resources
Richard Wolfson. Energy, Environment, and Climate. Second Edition, WW Norton, 2011.
- This is a great introductory-level textbook that covers climate science much better than most. Chapters 12--15 cover the greenhouse effect, forcings and feedbacks, observations, and future climates.