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
Multiple Process
Photosynthesis
Biofuels
BIOFUEL (1)
Keeling Curve
KLGSEASON (1)
BIOFUEL (2)
SOILCARB (3)
Transformation – Plant to Soil
Respiration – Decomposition
CARBRESB (3b),
AMAZON (7)
CARBATM (4)
FALEAVEA (5a)
FALEAVEA (5a),
FALEAVEB (5a)
SOILCARB (3)
FALEAVEA (4a)
FALEAVEA (4a),
FALEAVEB (4b)
Combustion BIOCOMBUST (5)
Atmosphere – Greenhouse effect GLOBWAMC (2)
Carbon Residency Time
Biofuel Production
CARBRESA (3a)
BIOFUEL2 (4)
QANGASCO (5)

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
Level
Principled reasoning
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 transformation of reactants into products in ways that conserve atoms at the atomic-molecular scale and mass at larger scales.
Less than completely successful attempts to conserve matter.
3
2
Mixed reasoning
Informal reasoning
No attempt to make connections across scales for questions posed at macroscopic scale
Inappropriate use of macroscopic scale ideas at other scales
Reactants and products described as material kinds, but atoms not traced through chemical processes and matter-energy transformations may be used as a
“fudge factor.)
Material inputs or needs and products or results are mentioned, but not in ways that clearly distinguish matter, energy, and conditions.
No indication that the student is reasoning about transformation of matter: no account of how material inputs are transformed into results.
1a Missing data (e.g. responses or codes lost after exam was taken and coded)
1b Student did not reach question
1c Student skipped question
1d
I don’t know or equivalent
1e 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
4 - Scientific
3 - Mixed
2 - Informal
Example Student Responses
-There is less plant activity in the winter and spring, allowing less CO2 to be taken up, and vice versa.
- Plants die in the winter, therefore there is a buildup of CO2.
- In Hawaii, the sun is closer in the winter and spring and plants thrive and produce CO2.
-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.
Description
-Students make a connection between graph oscillations and biological processes with clear mechanisms (photosynthesis fixing CO
2
or respiration releasing CO
2
)
-Students make a connection between graph oscillations and plant growth, but the mechanisms aren’t clear.
-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
4 - Scientific
Example Student Responses
- CO2 levels increase from 1960-2000 because of the increased usage of fossil fuels.
3 - Mixed
2 - Informal
-Human made pollutants from cars, factories, etc. weaken the atmosphere and trap more CO2
-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.
-More plants, trees, awareness
-Global warming
Description
-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)
-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.
-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
4 - Scientific
3 - Mixed
2 - Informal
Example Student Responses
Biofuels remove Co2 while growing along with the CO2 they release when burning staying mostly carbon neutral. Fossil fuels have no CO2 balance.
A)-Biofuels are more organic substances that when combusted do not let off CO2 admissions.
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.
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.
-Fossil fuels burn up the ozone layer, increasing climate change, biofuels are more environment friendly option.
Description
-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.
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.
B) Students understand oxidation of biofuels releases
CO2, but they do not reference the fact that plants remove CO2 from the atmosphere while growing.
-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 CO
2
.
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
4 - Scientific
Example Student Responses
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.
3 - Mixed A) Because the plants would be taking in the carbon dioxide ultimately increasing the level in the soil.
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.
B) The crops wouldn't take in all the carbon dioxide anymore, so the soil could take it in.
2 - Informal A) More vegetation would grow.
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).
Description
Student response accounts for differences in photosynthesis and respiration in the two ecosystems that leads to soil carbon changes
Students make an attempt to trace matter through photosynthesis, respiration or crop harvest, but either
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) 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)
Students make no attempt to trace matter through biological processes, including but not limited to
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
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.
3 - Mixed A) They decompose and/or get eaten by bugs.
A) They decompose and put off carbon dioxide during their decomposition.
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.
Description
Students describe decomposition leading to leaf matter moving to the soil / soil organisms as well as the atmosphere.
A) Students mention decomposition in soil, but only trace the leaves to either the soil or the atmosphere, but not both.
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 CO
2
.
Coding Rubric
Code Example Student Responses
4 - Scientific Yes, They are dead and bacterias will release carbon dioxide from decomposing them through cellular respiration.
3 - Mixed A) Yes, “As they decompose the release elements into the air”
B) Yes, “because they are not absorbing the
CO
2
causing the level to rise”
C) No, “because all of the carbon in leaves enters soil and then atmosphere”
Description
Student chooses Yes, and describes how decomposers release CO2 to the atmosphere with clear mechanism via cellular respiration
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) 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.
Student chooses No and reiterates that there’s no way the process influences carbon dioxide levels
2 - Informal
No: “Currently they have no effect, however their ancestors from long ago are contributing to the rise in CO
2
levels as they are burned as fossil fuels”

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: C
8
H
18
.)
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
4 - Scientific
Yes, “Other reactants (O2) combine with the gas when burned”
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.
2 - Informal No
Description
Student chooses Yes and describes that there are more reactants in the oxidation process.
A) Student chooses Yes but does not cite that there are other reactants
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.
Student chooses No and gives no explanation or says I don’t know.