Understanding Climate Change DQC’s
What knowledge does a student, or citizen, need in order to understand a scientific document about
climate change, such as the reports published by the Intergovernmental Panel on Climate Change? In
addition to understanding the scientific method, students must decipher the complex chemical,
biological and physical processes involved in the accumulation of atmospheric greenhouse gases and the
ability of those gases to absorb infrared radiation reflected from the Earth’s surface back towards the
atmosphere. At the heart of understanding this complexity is tracing matter, particularly carbon, and
tracing energy associated with carbon containing molecules. Biofuels and Keeling Curve are two
parallel Diagnostic Question Clusters (DQC’s) that are intended to diagnose problems in student
reasoning about the processes involved in global climate change. Following an initial multiple process
question, students are asked about individual processes contributing to the multiple process question.
The names of individual questions categorized by process are shown in the table below.
Processes
Biofuels
Keeling Curve
Multiple Process
BIOFUEL (1)
KLGSEASON (1)
BIOFUEL (2)
Photosynthesis
CARBRESB (3b),
AMAZON (7)
SOILCARB (3)
Transformation – Plant to Soil
CARBATM (4)
FALEAVEA (5a)
SOILCARB (3)
FALEAVEA (4a)
Respiration – Decomposition
FALEAVEA (5a),
FALEAVEB (5a)
FALEAVEA (4a),
FALEAVEB (4b)
Combustion
BIOCOMBUST (5)
QANGASCO (5)
Atmosphere – Greenhouse effect
GLOBWAMC (2)
Carbon Residency Time
CARBRESA (3a)
Biofuel Production
BIOFUEL2 (4)
General Instructions for Coding DQC Responses
Responses to DQC questions can be grouped into three general categories; Informal, Mixed or
Scientific. These three categories encompass a wide range of reasoning abilities, but all three categories
are common among college students. The table below describes the general types of responses that
would be associated with each level of reasoning. In addition, the levels of reasoning are assigned a
numerical value for coding purposes. Codes 2-4 are used for responses that attempt to answer the
question, while codes 1a-1e are reserved for missing responses or those that provide no information
about student reasoning. Mixed reasoning presents itself in several different ways, thus level 3 answers
are divided up into subcategories to reflect different types of responses.
Code
4
3
2
1a
1b
1c
1d
1e
Level
Scale
Successful use of
other scales to
explain macroscopic
phenomena
Processes described
in terms appropriate
for that scale
Partially successful
attempts to connect
scales, but with some
inappropriate use of
macroscopic ideas at
other scales
Matter
Reactants and products described
as chemical substances
Accounts of processes describe
Principled
transformation of reactants into
reasoning
products in ways that conserve
atoms at the atomic-molecular
scale and mass at larger scales.
Less than completely successful
attempts to conserve matter.
Reactants and products described
as material kinds, but atoms not
Mixed
traced through chemical processes
reasoning
and matter-energy
transformations may be used as a
“fudge factor.)
No attempt to make
Material inputs or needs and
connections across
products or results are mentioned,
scales for questions
but not in ways that clearly
posed at
distinguish matter, energy, and
macroscopic scale
conditions.
Informal
Inappropriate use of
No indication that the student is
reasoning
macroscopic scale
reasoning about transformation of
ideas at other scales
matter: no account of how
material inputs are transformed
into results.
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
Energy
Forms of energy are clearly
identified and distinguished
from forms of matter.
Energy transformation
described in ways consistent
with energy conservation.
Energy is recognized as a
distinct entity, but sometimes
in ways that do not clearly
distinguish energy from matter
(e.g., glucose, ATP) and/or
conditions (e.g., temperature).
Accounts fail to conserve
energy.
“Energy” used in an informal
sense as something that makes
events happen.
No clear distinction between
energy sources and other
needs or inputs.
These general ideas for coding above are applied to each individual question below to provide specific
details for how to code each question. Still, you will find that the specific coding rubric for each
question does not list every possible answer that you might see. In these cases, refer back to the general
rubric above, and try to be as objective as possible. You will undoubtedly find responses that don’t quite
fit a specific category, but seem to be in between. For these scenarios, we suggest that you assign a 2.5
or 3.5 code to the student.
Keeling Curve Diagnostic Question Cluster
Diagnostic Guide
Please answer the questions below as carefully and completely as you can.
1. The graph given below shows changes in concentration of carbon dioxide in the atmosphere over a
47-year span at Mauna Loa observatory at Hawaii.
1a. Why do you think this graph shows atmospheric carbon dioxide levels decreasing in the summer and
fall and carbon dioxide levels increasing in the winter and spring?
Correct, Scientific Answer: The graph shows these intra-annual oscillations because of the balance between photosynthesis
and respiration by organisms on Earth. During the summer in the Northern Hemisphere, plants are growing,
photosynthesizing, and taking carbon dioxide out of the atmosphere. In the winter, plants are not growing, and
photosynthesize, but plants, animals, microbes and other organisms are still respiring, thus releasing carbon dioxide to the
atmosphere.
Processes = Photosynthesis, Digestion/Biosynthesis, Respiration, Principles = Matter, Scale, Scale = Ecosystem ->
Atomic/Molecular
Purpose of Question: Here, we’re asking students to make a connection between the cellular processes of photosynthesis
and respiration to a large scale phenomenon: atmospheric composition. Students struggle to provide responses that aren’t
centered on human dimensions, but instead incorporate the differences between photosynthesis and respiration at different
times of the year. Many answers focus on the amount of fossil fuel use for driving and/or heating homes. Although this is
driving the upward trend overall, it reveals that the students aren’t reasoning about carbon transformations across “natural”
and anthropogenic processes similarly.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
-There is less plant activity in the winter and
spring, allowing less CO2 to be taken up, and
vice versa.
-Students make a connection between graph
oscillations and biological processes with clear
mechanisms (photosynthesis fixing CO2 or
respiration releasing CO2)
3 - Mixed
- Plants die in the winter, therefore there is a
buildup of CO2.
-Students make a connection between graph
oscillations and plant growth, but the mechanisms
aren’t clear.
- In Hawaii, the sun is closer in the winter and
spring and plants thrive and produce CO2.
2 - Informal
-It’s really hot there in the summer so the plants
stomas close creating less CO2.
- We use more energy in the winter because it is
getting colder. Spring is still cold and we are
using more energy to heat our homes and it gets
converted into CO2.
-Students make no accurate connections between
biological processes and graph oscillations.
1b. Why do you think the levels of carbon dioxide have increased from 1960 to present?
Correct, Scientific Answer: Human
activities such as the combustion of fossil fuels and land use change (e.g.
decomposition of organic materials and less photosynthesis) have resulted in large amounts of carbon
dioxide released to the atmosphere via oxidation of organic carbon containing molecules. These
activities continue year after year, causing the increase in atmospheric carbon dioxide levels over time.
Processes = Photosynthesis, Respiration, Combustion, Principles = Matter, Scale, Scale = Ecosystem > Atomic/Molecular
Purpose of Question: This question asks students to identify the source of carbon dioxide that is driving
a continual increase in the atmospheric concentration, which comes back to balancing sources and sinks
for carbon dioxide, and how humans have manipulated these processes. Many students acknowledge the
excess carbon dioxide being emitted from human activities. Still, some attribute the sharp rise to
volcanic activity or natural cycles.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
- CO2 levels increase from 1960-2000 because of
the increased usage of fossil fuels.
-Students make connection between rising CO2
levels and human activities responsible for excess
CO2 production, identifying the specific processes
that produce CO2 (combustion/usage of fossil fuels,
possibly land use changes)
3 - Mixed
-Human made pollutants from cars, factories,
etc. weaken the atmosphere and trap more CO2
-Students make connection between human activities
and rising CO2 levels, either accurately identifying
sources without specifying processes or accurately
identifying processes while suggesting that
something other than CO2 is a key product.
-More cars are polluting the air and the plants
can’t keep up.
- More people are contributing to the CO2 levels.
Also cars and other machines have become more
available.
2 - Informal
-More plants, trees, awareness
-Global warming
-Students make no accurate connection between
rising CO2 levels and human activities contributing
to the rising levels.
2. Explain why the use of biofuels instead of fossil fuels is a proposed strategy to slow the rate of global
climate change. Use as much detail in your answer as you can.
Correct, Scientific Answer: Biofuels are made from plants that were recently grown. Both biofuels and fossil fuels are
converted to carbon dioxide when combusted, but the carbon that is contained in biofuels was recently converted to organic
carbon through photosynthesis, and would have been returned to the atmosphere via decomposition of the plant material
anyway. Thus, burning biofuels contributes no net increase in atmospheric carbon dioxide levels, which are the primary
cause of climate change. The carbon contained in fossil fuels has been located in solid and liquid form in the Earth for
millions of years, and would not be expected to be converted to carbon dioxide by natural processes. Therefore, burning
fossil fuels does result in a net increase in atmospheric carbon dioxide levels.
Processes = Photosynthesis, Respiration/Combustion, Principles = Matter, Scale, Scale = Ecosystem -> Atomic/Molecular
Purpose of Question: In order to explain why biofuels are considered to reduce the effects of climate change, students need
to understand that the carbon dioxide released during biofuel combustion was recently taken out of the atmosphere via
photosynthesis, whereas fossil fuels have been located in the ground for millions of years and would not be released to the
atmosphere without human intervention. Students A) think that biofuels result in less carbon dioxide emissions than fossil
fuels when burned, failing to trace carbon during combustion, B) say that biofuels don’t give off greenhouse gases at all,
(similar reasoning to A, but essentially seeing fossil fuels as unnatural and biofuels as “natural”), C) Fail to recognize the age
of organic carbon in biofuels and fossil fuels, D) confuse the greenhouse effect with ozone layer depletion.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
Biofuels remove Co2 while growing along with
the CO2 they release when burning staying
mostly carbon neutral. Fossil fuels have no CO2
balance.
-Student explains that carbon dioxide released from
biofuels during combustion is part of a short term
carbon cycle (plants remove CO2 from atmosphere
while growing, and most of this carbon would be
oxidized by decomposers soon after plant death.
3 - Mixed
A)-Biofuels are more organic substances that
when combusted do not let off CO2 admissions.
A) Student references greenhouse gases, CO2 or other
specific matter containing compounds in relation to
the combustion of biofuels, but cites incorrect facts,
such as the idea that biofuels do not emit, or emit less
CO2 or greenhouse gases when burned.
A) They do not emit greenhouse gases like fossils
fuels. They will not create a heat trapping smog.
That doesn’t allow heat to escape.
2 - Informal
B) Biofuels are actually just as bad as fossil
fuels. Both emit carbon dioxide into the air.
Biofuels take up a lot of land and aren't very
efficient. Biofuels cause bacteria to grow in the
soil that puts more carbon dioxide into the air.
Biofuel is not alternative strategy to fossil fuels.
B) Students understand oxidation of biofuels releases
CO2, but they do not reference the fact that plants
remove CO2 from the atmosphere while growing.
-Fossil fuels burn up the ozone layer, increasing
climate change, biofuels are more environment
friendly option.
-Student does not reference specific matter containing
entities in relationship to the combustion of biofuels.
Often, students repeat common “environmental”
slogans they’ve heard, sometimes including the ozone
layer.
3. Scientists would suggest that carbon in the soil would increase if farmers stopped growing crops and
let the abandoned land turn to grassland or forest. Why would this increase in soil carbon occur?
Carbon dioxide is transformed to organic carbon via photosynthesis in plants. This organic carbon
moves to the soil via dead plant and animal material. Crop harvest results in the removal of organic
matter from the ecosystem, which reduces the amount of carbon entering the soil. In addition,
cultivation processes enhance decomposition of soil organic matter, which releases carbon to the
atmosphere as CO2.
Processes = Photosynthesis, Transformation, Principles = Tracing Matter, Scale = Ecosystem
Purpose of Question: This question asks students to realize that carbon is removed in crop material.
Therefore, when crops are no longer grown, more dead plant material is present to enter the soil organic
matter pool. In addition, cultivation of annual crop plants enhances the decomposition of soil organic
matter. Discontinuation of cultivation will result in more perennial plants and less soil disturbance. Most
students recognize that harvested crop biomass contains a large amount of carbon that is not entering the
soil at the end of the year, but rarely recognize that cultivation practices result in the depletion of soil
organic carbon.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
Farmers remove crops as produce, from plants
that would have otherwise died, decayed and
returned atmospheric carbon to the soil. Wild
forest/grasses would do this effectively through
photosynthesis.
Student response accounts for differences in
photosynthesis and respiration in the two ecosystems
that leads to soil carbon changes
3 - Mixed
A) Because the plants would be taking in the
carbon dioxide ultimately increasing the level in
the soil.
Students make an attempt to trace matter through
photosynthesis, respiration or crop harvest, but either
A) Instead of plants being harvested and eaten by
animals - they would continually grow and the
waste would be absorbed into soil + not eaten.
B) If the plants in the soil decompose, they will
leave their carbon in the soil.
2 - Informal
A) Only refer to one matter transforming process
instead of integrating processes (e.g. Reference
only to higher photosynthesis rate in
forest/grassland, Reference only to higher
respiration rate in cropland, Reference only
carbon removed in crop material) OR
B) The crops wouldn't take in all the carbon
dioxide anymore, so the soil could take it in.
B) Include incorrect details about carbon
transforming processes (e.g. Plants use soil
carbon for growth, Soil takes in CO2 directly,
Respiration in soil leads to more soil carbon
(misconception), decomposition positively
correlated with soil carbon buildup)
A) More vegetation would grow.
Students make no attempt to trace matter through
biological processes, including but not limited to
B) Crops use the carbon.
C) The fertilizer or harsh chemicals they put in
the soil would dissolve and then become more
fertile if left alone for a while.
Carbon becomes more prevalent over periods of
time (with rest or no growth).
A) Plant growth causes soil carbon to form
B) Crops “use” or “use up” soil carbon to grow
C) Human influence causes difference (e.g.
Fertilizers or pesticides cause difference (without
mentioning mechanism by which this could
happen)
4a. In the fall, the leaves on trees in a deciduous forest fall to the ground. Explain what happens to the
leaves once they fall to the ground.
The leaves are decomposed by soil organisms. The matter in the leaves is lost as carbon dioxide and
water as the decomposers break down the organic substances in the leaves.
Processes = Respiration, Transformation, Principles = Tracing Matter, Scale = Organismal
Purpose of Question: Part A of the question assesses whether students understand that decomposers use
discarded plant tissue as a source of carbon and energy. Part B assesses whether students see a link
between decomposition and atmospheric carbon dioxide. A matter-tracing answer to Part A would
follow the carbon, hydrogen, oxygen, and other elements into CO2, H2O, and soil minerals.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
Bacteria decomposes them. Some carbon
dioxide is released into the air and the other
nutrients are used by the bacteria or left in
the soil.
Students describe decomposition leading to leaf
matter moving to the soil / soil organisms as well
as the atmosphere.
3 - Mixed
A) They decompose and/or get eaten by
bugs.
A) They decompose and put off carbon
dioxide during their decomposition.
A) Students mention decomposition in soil, but
only trace the leaves to either the soil or the
atmosphere, but not both.
A) They are broken down into organic
matter in the soil.
B) The leaves decompose and give energy to
the soil to help with the growth of new life.
C) They are decomposed by bacteria.
2 - Informal
B) They are no longer absorbing nutrients or
can't handle it because of the old age.
B) They begin to die.
C) The carbon cycle absorbs the leaves into
the soil.
B) Students convert matter to energy by
describing that the leaves are used for energy in
the soil.
C) Students mention decomposition without
referring to any product of the decomposition
process.
B) Students make no mention to processes
occurring after the leaves fall or matter resulting
from the leaves
C) Students describe the leaves moving to the
soil without reference to any biological processes
(e.g. the soil absorbs the leaves).
4b. Do the changes in the dead leaves affect atmospheric carbon dioxide levels? Circle Yes or No.
Why or why not?
Plants absorb carbon dioxide from the atmosphere during photosynthesis, thus removing carbon dioxide
from the atmosphere. Decomposers that break down the leaves release carbon dioxide to the
atmosphere, thus increasing carbon dioxide levels back to where they were before the plant produced
the leaves.
Processes = Respiration, Transformation, Principles = Tracing Matter, Scale = Organismal
Purpose of Question: Part A of the question assesses whether students understand that decomposers use
discarded plant tissue as a source of carbon and energy. Part B assesses whether students see a link
between decomposition and atmospheric carbon dioxide. A matter-tracing answer to Part A would
follow the carbon, hydrogen, oxygen, and other elements into CO2, H2O, and soil minerals. Part B
would then be redundant. Note, though, how different the students’ answers to Parts a and b tend to be.
Part a responses mention the leaves going into the soil or energy, but not CO2. Part B responses that
mention decomposition releasing CO2 still often fail to mention the origins of the carbon. Most students
think that leaves will decompose. Some students have difficulty seeing a link between decomposition of
the dead leaves in the soil and atmospheric gasses, specifically CO2.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
Yes, They are dead and bacterias will
release carbon dioxide from decomposing
them through cellular respiration.
Student chooses Yes, and describes how
decomposers release CO2 to the atmosphere with
clear mechanism via cellular respiration
3 - Mixed
A) Yes, “As they decompose the release
elements into the air”
A) Student chooses Yes, but does not refer to
specific biological process by which carbon
dioxide is released from leaves, but implies a
hidden mechanism (e.g. decomposers release
CO2 to atmosphere).
B) Yes, “because they are not absorbing the
CO2 causing the level to rise”
C) No, “because all of the carbon in leaves
enters soil and then atmosphere”
B) Student chooses Yes and refers to less
photosynthesis because the leaves have died.
C) Student chooses No and describes multiple
steps in which it influences carbon dioxide levels.
2 - Informal
No: “Currently they have no effect, however
their ancestors from long ago are
contributing to the rise in CO2 levels as they
are burned as fossil fuels”
Student chooses No and reiterates that there’s no
way the process influences carbon dioxide levels
5a. Do you think the following statement can be correct? Circle Yes or No.
One gallon of gasoline, which weighs about 6.3 pounds, could produce 20 pounds of carbon dioxide
when burned.
5b. Explain your reasoning. How could the carbon dioxide weigh more than the gasoline, or why is this
impossible? (Note: Gasoline is a mixture of hydrocarbons such as octane: C8H18.)
During combustion, gasoline is not the only reactant in the equation. Oxygen in the atmosphere is
another reactant. The oxygen is combined with carbon atoms in the octane to produce carbon dioxide,
which is released to the atmosphere. The hydrogen atoms in the octane are incorporated into water
molecules, but the hydrogen atoms have little mass compared to carbon and oxygen.
Processes = Combustion, Principles = Tracing Matter, Scale = Atomic-Molecular
Purpose of Question: This question assesses whether students have an atomic-molecular understanding
of fossil fuel combustion. In order to correctly answer the question, students must know the reactants
and products of the equation and that atoms have different weights, so molecules have different weights.
Unprincipled thinking could result in a “No” answer, accompanied by an explanation that fails to
incorporate all reactants in the combustion process, or fails to trace matter through the process.
Coding Rubric
Code
Example Student Responses
Description
4 - Scientific
Yes, “Other reactants (O2) combine with the
gas when burned”
Student chooses Yes and describes that there are
more reactants in the oxidation process.
3 - Mixed
A) Yes, “It could weigh more because gas
expands, so it will occupy a larger area” B)
No, “A pound of feathers and a pound of
bricks is still a pound”
C) Yes, I have no idea.
A) Student chooses Yes but does not cite that
there are other reactants
No
Student chooses No and gives no explanation or
says I don’t know.
2 - Informal
B) Student chooses No and refers to, or implies,
the idea of conservation of mass.
C) Student chooses Yes and gives no explanation
or says I don’t know.