Download Unit 3 Lecture Notes (4 Parts, 100+ minutes total class time

Unit 3 Lecture Notes (4 Parts, 100+ minutes total class time)
Learning goals
1. Differentiate between climate sensitivity and future emissions as distinct sources of
uncertainty in our projections of future climate change.
2. Quantify the social costs of climate change with a global Dynamic Integrated Climate
Economy model.
Collect Unit 3 homework and return Unit 2 homework (presumably ungraded).
Part 1: Modeling climate change (30+ minute Lecture & discussion)
In Parts 2 and 3 of this unit, students will use webDICE to model the economics of climate
change. This opening discussion encourages the students to apply systems thinking and
consider the role of models in building our understanding of the climate change problem.
Slide 1: Begin working with students on a system diagram (or concept map) on the board that
describes what we have covered to this point in the module. Start with carbon emissions. How
do carbon emissions affect the Earth System? Ask students to help you map out the
consequences of carbon emissions. If your students are new to concept mapping you may need
to do a fair bit of leading this discussion and/or allow for more time.
Slide 2 shows a sample of what you might expect to come up with to describe Units 1 & 2. We
expect responses to vary tremendously from class to class (see another example in the
webspace). The key points that students should carry forward into the following units are
shown on this slide. This diagram is equivalent to the green (right) half of the Module System
Diagram included in the extra slides for Unit 2. It is the environmental portion of the socioenvironmental system described in this module and built upon at the end of this unit.
Emphasize the feedbacks and the challenges they present to predicting global temperature. Ask
students: Given all the feedbacks, how do we predict future temperature?
Slide 3: We use models. Models are simplifications of the real world. They are tools that we use
to describe or test our understanding of how something works. They can be as simple as a
single equation (i.e., a regression model) or highly complex sets of equations that describe
interconnected processes (i.e., global circulation model). Instructors can decide how much
detail about models is necessary and appropriate for their course. The take home message for
the slide is: We build models with algorithms that describe processes and then force the model
with inputs to make predictions about the future (we call these outputs). For introductory
students, it's worth revisiting the exact examples from the animated powerpoint or else using
your own favorite model analogy. Unit 1 showed output from General Circulation Models.
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Ask students: What physical processes should be included in a model to predict the
temperature of the planet? This is essentially the same question from the Unit 2 homework
collected at the start of class. The idea is to get them thinking about feedbacks in the context of
models. Answer: All the feedbacks shown in Slide 4. We suggest picking one or two feedbacks
suggested by students to discuss further.
Virtually every topic that your students will come up with will require systems thinking to
understand, so the one or two that you discuss should emphasize forcing and feedbacks. Here's
an example:
A student says we could include that plants inhale carbon dioxide. Emphasize to
them that this isn't an isolated system: there is a symbiotic relationship between
plants inhaling it, animals exhaling it, and plants releasing it as they decay. The
process of decay gives back the CO2 and it also releases nutrients to the ground,
which allows more plants to grow, etc. All of these processes could be included in
the different components, and the process just described is included in many
models.
Transition to webDICE. You may want to pull the model web interface up on the screen with the
hyperlink that appears with click on Slide 4. Explain that they have read about and will now use
webDICE, a web-based Dynamic Integrate Climate Economy model.
Based on their reading of webDICE documentation, ask students: What does webDICE do?
Suggest writing succinct references to these on the left half of the board. Student responses
should be highly varied given the lack of specificity. This is good! webDICE is a simplified version
of a “widely-used model of the economics of climate change” that allows users to estimate
future warming and the associated costs to society under different model scenarios. In class,
they will use it to generate a Data Table of predictions of temperature change and the Social
Cost of Carbon curve (see webDICE Student sheet).
Students will use webDICE output generated in class to answer questions in the webDICE
Assignment outside of class. For introductory courses (and even most upper-level courses), it
would be wise to plant the seeds of these questions as explicitly and obviously as possible so
that they are not surprised when they get home. It was our experience that students struggled
more with webDICE than anything else in the module.
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Ask students: What are some components of the webDICE model? Inputs? Algorithms?
Outputs? Write student responses to these out on the board, separating them into inputs (called
"parameters") on the left, outputs on the right, and guts (processes described by algorithms) in
the middle. I choose to not tell my students why I'm writing on the left, middle, or right, and
explain why I did that at the end. You can revisit these lists when you demo the webDICE model
in Part 2. A point to make here (which is a question on the webDICE assignment below): Models
use inputs (e.g. climate sensitivity, types of policies we will implement, how expensive it will be
to switch away from fossil fuels) to generate outputs (e.g., global temperature rise, amount of
sea level rise, ocean acidification, etc.). To make these predictions, the guts of the model are
equations that describe our understanding of how the world works (e.g., equations of motion,
physical relationships between air and water, plants and air, etc.).
Return to Slide 4. Ask students: How does the webDICE model account for the feedbacks that
we discussed? Answer: In the webDICE model, all of the feedbacks are represented by one
number: climate sensitivity. webDICE uses climate sensitivity as the "dial" that you can turn to
represent scientific uncertainty about warming due to feedbacks in the climate system.
Slide 5: Remind students that equilibrium climate sensitivity is the amount that the world will
warm (due to feedbacks) if we double carbon dioxide concentrations above their pre-industrial
value (thereby creating a climate forcing) and then wait for the world to come back into
equilibrium - most likely 3.2°C of warming for a doubling of CO2 with likely range is between
1.6°C and 4.4°C. Note these are slightly different than IPCC estimates because the webDICE
model only allows you to change climate sensitivity in increments of 0.2°C.
Draw the connection between the simple equilibrium "model" that they already learned about
and the more complicated webDICE model that they will now work with (and that they just
described), which is a simplification of an even more complex model used by researchers to
understand feedbacks in the real-world climate, economic, and policy system.
Helpful Hint: A question on the webDICE assignment introduced in Part 2 asks:
Your friend (who is not in this class) asks you to explain the following statement that
summarizes the findings in the IPCC AR5 Report: 'Equilibrium climate sensitivity is likely in the
range 1.5°C to 4.5°C, with a most likely value of 3.2°C.' What do you say? Use one of the
feedbacks from the activity in Unit 2 as a specific example in your explanation of climate
sensitivity."
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You may want to explicitly answer this question in class (see Solutions to the webDICE
assignment for a discussion of this). The whole concept of climate sensitivity can be very
confusing to the students. They tend not to understand its connection to feedbacks. Climate
sensitivity is often just given in the unit of degrees Celsius, which can be confusing. Some of our
students thought that climate sensitivity was an output of the webDICE model, not an input. You
many need to explain that climate sensitivity is output from other models (e.g., GCMs) and use
as input to webDICE.
Slide 6: Are there situations in which webDICE's output will be of limited value or potentially
misleading? An example that you might use if your students struggle to get started: There is a
parameter that allows the user to set "Maximum Global Population." This has obvious
implications to global energy use (among many other things), but is a fundamentally uncertain
input going into the model. You can diagram this out a bit. What if we overestimate the world's
population? Consumption and energy use would also be overestimated, and there are any
number of ways that could give us the "wrong" prediction for the future of the climate. You can
draw this as a system diagram that is very similar to the way we drew feedback loops in the
previous class. Hopefully students are learning to think about climate change as a systems
problem, characterized by interrelated variables and significant uncertainties. Point this out to
the students.
Slide 7: Clarify, webDICE isn’t intended to predict the future. It’s a tool that provides insights
into important drivers and potential outcomes of climate change based on an understanding of
how the climate system and global economy are related.
Slide 8: Transition to webDICE modeling activity. Follow the step by step webDICE Instructor
sheet to demonstrate webDICE to the students. This document will move you and your class
through the operational details of the model. Note: the text in red are things worth pointing
out to your students that are not in their webDICE Student Instructions. Many of these points
connect back to the discussion questions just covered, so please do make those connections
explicit.
Part 2. Predicting climate change with webDICE (25+ minute Small group activity):
After completing the steps in webDICE Instructor sheet in front of the class, distribute the
webDICE Student sheet (also available for viewing and download on the Student Materials
page). In pairs or small groups have the students follow the step by step instructions under Task
A of the webDICE Student sheet to fill in the Data Table need to complete Part II of the
webDICE Assignment outside of class.
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Give the students about 15 minutes to manipulate webDICE and fill in the Table and bring their
attention back to class. This is a potential break point for a short class period and students can
finish Task A at home before the next class.
Slide 9: Ask students for the values to fill in the Table (or if you want to show the completed
table it’s in webDICE Solutions).
Slide 10 shows the output of Task A. Ask students: Which input parameter results in more
variability in future warming, “climate sensitivity” or emissions – as represented by “Business as
Usual” or “Optimized Policy”? Answer: Changing emissions (i.e., Policy) results in greater
variability than changing the scientific uncertainty represented in webDICE by “climate
sensitivity.” Note that under all model scenarios, there is warming. Then transition to the Social
Cost of Carbon and the next webDICE task.
Part 3. Estimating the Social Cost of Carbon Class with webDICE (25+ min Small group activity)
Ask students: How much global warming should concern us? Answers might vary from all of it
to none of it. Some people are moved by the impacts to nature and wildlife depicted in the
media and described in the NCA. Others, including many policy makers, are more motivated by
estimates of the projected cost of climate change impacts (or “damages” in economic terms) to
cities, states, and nations. Collectively, these costs are referred to as the Social Cost of Carbon
(SCC). In the next activity, students use webDICE to generate SCC curves.
Slide 11. Ask students to define the social cost of carbon. Answers will vary, but the main point
is: The social cost of carbon is a measure, in dollar terms, of the damages that occur as a result
of the impacts from climate change due to an additional ton of carbon emissions. A suggested
factoid: Hurricanes Sandy and Katrina are both estimated to have cost about $65 billion dollars
in recovery efforts. If you do use this, be careful in your wording. You don't want to blame these
storms on climate change, but rather use them as examples of expensive natural disasters. In
the future, we expect that extreme events and natural disasters such as hurricanes will increase
in intensity, and we know that they are expensive to clean up.
Direct students to work on Task B of the webDICE student sheet. Remind them that the Figures
they make when following the instructions will be needed to answer the questions in Part III of
the webDICE Assignment. If they are doing Task B in the same class period as Task B. Instruct
them to Clear out prior model runs. Easiest way is to click on webDICE on top left and back to
Advanced Inputs. Give them about 15 minutes to work on the activity then bring their attention
back to the front.
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Slide 12: Ask students: Estimates of SCC are more sensitive to which input parameter, “climate
sensitivity” or “harms”? Answer: SCC is more sensitive to “harms” – the SCC might be much
higher if the harms induced by warming are larger than expected or lower if they are not. This
model suggests there is greater uncertainty with respect to the “harms” from climate change
than from the uncertainty in “climate sensitivity.”
You can note that current emissions are about 10 GtC /yr. Ask students what is the social cost of
emitting an additional ton of CO2 at current emissions levels. It’s about $20/ton CO2. (10 Gt C ≈
36 Gt CO2 ).
If you haven’t already, you can distribute the webDICE Assignment (or direct them to Student
Materials page to download). Remind them that they follow steps in Task A to complete Part II
of the Assignment and Task B for Part III. We recommend giving students a week to complete
the webDICE Assignment and collecting it during Unit 5. There’s a grading rubric included in the
assignment to guide the students as they prepare their answers. An answer key, webDICE
Solutions, is available in the web space for instructors.
Part 4. Summarize with Systems Thinking (15+ minute Discussion)
While continuing to show Slide 12, ask students:
 Who will pay these costs of climate change?

What can/should we do about it as individuals? as communities? as nations?
You can write student responses on the board in 3 lists corresponding to these categories. The
goal with discussion is to have the students brainstorm and foreshadow upcoming material in
the module. Hopefully, someone will suggest policy. If not, you can ask them about the
webDICE input parameter for policy “Business as Usual” vs. “Optimized” that they manipulated
in Part 2/Task A. What does this parameter represent? - It represents whether or not we take
collective action, in the form of policy action, to limit carbon emissions.
Slide 13: Shows an incomplete version of the Module System Diagram. Remind students that
the overarching purpose of this module is to explore the dynamic relationships among science,
economics and policy relative to climate change. At this point, we have examined the causes
and effects of climate change (Unit 1), the link between emissions and the greenhouse effect
(Unit 2) and today used a global climate-economy model to estimate the costs of climate
change to humanity. End class asking them to consider: What might encourage a government
or individual decision maker to launch a policy-making process to address climate change? The
next unit examines the responsibility of the U.S. in creating global climate change and the
creation of the first federal policy to regulate carbon emissions to mitigate it.
Unit 3 Lecture Notes
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