2. Gallery Walk: Anthropogenic Effects on Global C Cycle
Notes to faculty
Outcomes: The 4 questions help students better understand: specific
anthropogenic source(s) of atmospheric CO2, annual pattern of CO2 change in
the northern hemisphere, original source of C in fossil fuels, and “the missing
carbon”.
What students do: In this gallery walk there are 4 stations – locations in the room
where you post one of the questions below on a large piece of sticky easel-pad
paper or something similar. Teams of students start at one station and when you
say so, walk to the next. At each station student teams read the statement and
questions and address them as best they can; each group is given a distinctive
colored marker. Groups can comment on prior group’s statements and questions.
At the end, a student summarizes the statements and questions on one sheet. All
of this leads to discussion.
What to pay particular attention to:
o Question 1: Focus is two major anthropogenic activities that cause rising
CO2 (fossil fuel use is the first and land use change second;
http://www.whrc.org/carbon/index.htm). The U.S. used to be the main emitter of
CO2 but China may have exceeded us by now. Some students do not
know these facts. In interviews students often don't identify CO2 as the
primary reason for human-induced climate change, and often respond with
vague answers that list the ozone layer or pollution as factors. Also,
students don't trace carbon during combustion, often assuming that the
matter is "burned up" or converted to energy instead of being released as
CO2. Finally, many students do not understand the greenhouse effect and
attribute climate change to decreased ozone layer thickness or heat from
fossil fuel combustion.
o Question 2: The focus here is formation of fossil fuels (see
http://en.wikipedia.org/wiki/Fossil_fuel for information). Many students do
not recognize that the C emitted now is “ancient” and that it is organic
carbon that originated from photosynthesis protected from decomposition
for millions of years. Also see Question 1.
o Question 3: This question gives a little background about the Keeling
Curve and asks students about the insert figure. Many students will not
know about the annual pattern of CO2 during summer/winter or make the
connection between photosynthesis/respiration by organisms and global
changes in CO2.
o Questions 4: This is the most challenging question. The figure is unusual
in its set up, both in regard to the accumulation/release axis and the
stacked data. Most students won’t know what the “missing C” is, but this
will give them a chance to puzzled over it.
Logistics:
o A Gallery Walk is a good way to find out fairly quickly what students know
about a specific topic. This would give you an idea how much you need to
go over in class and particular points of confusion or misunderstanding.
The questions are related but independent of each other (e.g. students
don’t need to have read no. 1 before no. 2). The SERC URL below gives
detailed instructions.
o You can print out the questions and attach them to the sheets. You may
need to add extra sheets of paper as student comments fill them up, so be
prepared for this.
o You can do this exercise with a small class. Groups can be a small as 2
but should not be larger than 5. Have student count off the 4; 1s go to the
first station and so on. In a medium sized class you can have multiple
stations of the same questions if you figure out the logistics of moving that
many students around.
o You have to figure out logistical issues ahead of time such as keeping
students on task and in general be comfortable with an “uncontrolled”
exercise like this (e.g. it will be noisy). It will be new to most students and
therefore you need to explain the “rules”. Many students like it because it
gives them a chance to walk around and work in groups in a different way.
o In classes too large to do a Gallery Walk, you can use any of the figures in
discussion, as homework, a minute paper, etc.
Resources:
o Gallery Walk (http://serc.carleton.edu/introgeo/gallerywalk/how.html;
http://serc.carleton.edu/introgeo/gallerywalk/) and
http://tiee.ecoed.net/teach/teach_glossary.html
o Woods Hole Research Center Global C Cycle
(http://www.whrc.org/carbon/index.htm)
o
Nature Report on Missing C
(http://www.nature.com/climate/2007/0708/full/climate.2007.35.html)
Units & Quantitative Skills: Figure interpretation; units for carbon dioxide, global
carbon (Pg); C flux – what this means
Topics specific to the exercise: Missing carbon; global C measurements; Keeling
Curve; land use change effects on C cycling.
HIDDEN CURRICULUM
• Principles: Conservation of Matter: Carbon is conserved and can be
traced throughout the global C cycle.
• Processes: Generation (photosynthesis as ultimate source of C in fuels);
Transformation; Oxidation (e.g. fossil fuel oxidation).
• Scale & Time: links between atomic/molecular, cellular-organismal, and
ecosystem level processes in the global C cycle; processes over a month vs. a
year; global measurements as integrators of regional processes
• Forms & Representations: Global carbon flow; organic molecules as
form of potential chemical energy.
Student Directions
Gallery Walk: Follow your teacher’s instructions to address the
following questions:
1. We know from measurements taken in Hawaii at Manua Loa that Carbon
Dioxide (CO2) 38 concentrations have increased greatly since the 1960s –
from about 315 ppm to about 390 ppm now. This is of great concern
because CO2 is a greenhouse gas and contributes to global warming.
Which two countries do you think are mainly responsible for this rapid
increase in CO2? What human activities do you think is responsible for
this increase? Explain the process here – exactly how this activity results
in CO2 going into the atmosphere. Be as specific as you can be and write
down any questions you have.
2. When fossil fuels are burned for various uses, CO2 is released into the
atmosphere. What are fossil fuels? Where did the C in the CO 2 come
from in the first place and by what biological process? Be as specific as
you can be and write down any questions you have.
3. This is the well know Keeling Curve named after Charles Keeling, a
scientist from the Scripps Institution of Oceanography who started taking
measurements of atmospheric CO2 in Hawaii in1958. Clearly atmospheric
CO2 has increased during the period shown here. Explain the inserted
graph in the lower right and its relationship to the main curve. Write down
any questions you may have.
Source: http://en.wikipedia.org/wiki/Keeling_Curve
4. This graph shows yearly estimates of global flux (rate of change) of
Carbon (units are Pg, Petagrams or 1,000,000,000,000,000 or 1X10 12
grams) from various sources. First, make sure you understand the graph
(the axes, each category). Then interpret it. In particular, what is the
“unidentified sink”? What is a carbon sink – what does this mean? Be as
specific as you can be and write down any questions you have.
Source: http://www.whrc.org/carbon/images/Flux_of_Carbon.gif