Atmospheric carbon dioxide (CO2) has been increasing since 1700, but the amount of CO2 produced in that time by burning...
GMAT Reading Comprehension : (RC) Questions
Atmospheric carbon dioxide (CO2) has been increasing since 1700, but the amount of CO2 produced in that time by burning fossil fuels should have resulted in a much greater increase than has been observed. Plant ecologist Allen Auclair claims that the woodlands of the Northern Hemisphere have been acting as a carbon sink, absorbing carbon from the atmosphere and turning it into wood. Auclair uses measurements of factors affecting the area and density of a forest—such as logging, fires, and pests — and estimates of tree growth rates to argue that increases in the growth rates of individual trees in these forests since 1920 have created a large volume of wood that accounts for the missing carbon.
To determine whether the woodlands as a whole are releasing or absorbing carbon, the volume of wood added to the woodlands must be compared with the wood lost. Auclair's analysis of the past hundred years shows the woodlands changing from a carbon source to a carbon sink. Before 1890, northern woodlands were a source of CO2 mainly because of forest fires and logging. Such deforestation releases CO2 because debris from the forest floor rots more quickly when the trees are cleared. After 1920, the steep increase in tree growth rates surpassed the losses stemming from fire and logging, turning the northern forests from a carbon source into a carbon sink and storing CO2 from fossil fuel over the next fifty years.
The passage is primarily concerned
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| Atmospheric carbon dioxide (CO2) has been increasing since 1700, but the amount of CO2 produced in that time by burning fossil fuels should have resulted in a much greater increase than has been observed. | What it says: CO2 is going up, but not as much as scientists expected based on fossil fuel burning. What it does: Sets up a scientific puzzle/mystery that needs explaining Source/Type: Scientific fact presenting a discrepancy Connection to Previous Sentences: This is our opening - establishes the central mystery the passage will solve Visualization: Expected CO2 increase: 150 units Actual observed increase: 100 units Missing CO2: 50 units - Where did it go? What We Know So Far: There's missing CO2 that should be in the atmosphere What We Don't Know Yet: Where the missing CO2 went Reading Strategy Insight: This opening sentence establishes THE central question the entire passage will answer - keep this puzzle in mind as you read |
| Plant ecologist Allen Auclair claims that the woodlands of the Northern Hemisphere have been acting as a carbon sink, absorbing carbon from the atmosphere and turning it into wood. | What it says: Scientist Auclair thinks northern forests are absorbing the missing CO2 and storing it as wood What it does: Introduces the proposed solution to the mystery Source/Type: Researcher's claim/hypothesis Connection to Previous Sentences: This directly answers the question from sentence 1: the missing CO2 went into trees! This builds on our opening mystery by providing Auclair's proposed solution. Visualization: Missing CO2 (50 units) → Absorbed by northern forests → Stored as wood growth What We Know So Far: • Missing CO2 problem exists • Auclair's solution: forests absorbed it What We Don't Know Yet: How Auclair proves this theory Reading Strategy Insight: Feel confident here - we now have both the problem AND proposed solution. The rest will be supporting evidence. |
| Auclair uses measurements of factors affecting the area and density of a forest—such as logging, fires, and pests — and estimates of tree growth rates to argue that increases in the growth rates of individual trees in these forests since 1920 have created a large volume of wood that accounts for the missing carbon. | What it says: Auclair measured things that hurt forests (logging, fires, pests) and things that help forests (growth rates) to prove trees grew faster since 1920, creating enough wood to store the missing CO2 What it does: Explains Auclair's methodology and key finding Source/Type: Description of research method and conclusion Connection to Previous Sentences: This elaborates on HOW Auclair reached his conclusion from sentence 2. This is still supporting the same basic idea - not new complexity! Visualization: Auclair's measurement approach: • Forest losses: logging + fires + pests = 20 units • Forest gains: increased growth since 1920 = 70 units • Net wood volume gained = 50 units (matches missing CO2!) Reading Strategy Insight: This sentence gives us the crucial timeframe (since 1920) and shows Auclair's evidence supports his theory. We're still solving the same puzzle from sentence 1! |
| To determine whether the woodlands as a whole are releasing or absorbing carbon, the volume of wood added to the woodlands must be compared with the wood lost. | What it says: To know if forests help or hurt CO2 levels, you need to compare wood gained vs. wood lost What it does: Explains the logical framework for the analysis Source/Type: Methodological explanation Connection to Previous Sentences: This restates and simplifies the approach mentioned in sentence 3. The author is helping us understand the basic logic: gains vs. losses = net effect Visualization: Simple equation: Wood Added - Wood Lost = Net Carbon Effect If positive = carbon sink (absorbs CO2) If negative = carbon source (releases CO2) Reading Strategy Insight: Feel relieved here - this is simplification, not new complexity! The author is breaking down the methodology into basic math we can all understand. |
| Auclair's analysis of the past hundred years shows the woodlands changing from a carbon source to a carbon sink. | What it says: Over 100 years, northern forests switched from releasing CO2 to absorbing CO2 What it does: Presents Auclair's main finding - a dramatic change over time Source/Type: Research conclusion Connection to Previous Sentences: This applies the framework from sentence 4 to give us Auclair's key discovery. This directly supports his claim from sentence 2 by showing the forests DID become carbon absorbers. Visualization: Timeline of forest CO2 impact: 1800s: Forests = carbon source (releasing CO2) 1900s onward: Forests = carbon sink (absorbing CO2) What We Know So Far: • Missing CO2 mystery • Auclair's theory: forests absorbed it • His method: compare gains vs losses • His finding: forests switched from CO2 source to CO2 sink Reading Strategy Insight: This is the pivotal finding that supports Auclair's solution to our opening mystery. We're building toward the complete answer. |
| Before 1890, northern woodlands were a source of CO2 mainly because of forest fires and logging. | What it says: Until 1890, fires and logging made forests release CO2 What it does: Provides specific evidence for the first part of the timeline Source/Type: Historical evidence supporting the claim Connection to Previous Sentences: This gives us the specific details for the "carbon source" period mentioned in sentence 5. This is elaboration, not new information! Visualization: Before 1890: Forest fires + logging → damaged forests → CO2 released to atmosphere Net effect: Forests contributing TO the CO2 problem Reading Strategy Insight: The author is filling in historical details to help us understand the complete picture. This explains WHY forests used to be CO2 sources. |
| Such deforestation releases CO2 because debris from the forest floor rots more quickly when the trees are cleared. | What it says: When you cut down trees, the leftover plant material on the ground rots faster and releases CO2 What it does: Explains the scientific mechanism behind the previous statement Source/Type: Scientific explanation Connection to Previous Sentences: This explains HOW the logging/fires from sentence 6 actually released CO2. It's giving us the scientific "why" behind the historical fact. Visualization: Normal forest: Tree cover protects forest floor → slow decomposition After logging/fires: No tree cover → faster rotting → more CO2 released Reading Strategy Insight: This is helpful detail that explains the mechanism. The author is making sure we understand the science, not adding complexity. |
| After 1920, the steep increase in tree growth rates surpassed the losses stemming from fire and logging, turning the northern forests from a carbon source into a carbon sink and storing CO2 from fossil fuel over the next fifty years. | What it says: Starting in 1920, trees grew so much faster that forest gains beat forest losses, making forests absorb CO2 (including fossil fuel CO2) for the next 50 years What it does: Completes the timeline and directly connects back to our opening mystery Source/Type: Research conclusion with specific timeframe Connection to Previous Sentences: This is the payoff! This sentence connects directly back to our opening mystery from sentence 1. It explains the second part of the timeline from sentence 5 and shows how Auclair's theory solves our missing CO2 puzzle. Visualization: After 1920: Tree growth gains (100 units) > Fire/logging losses (30 units) Net result: 70 units of CO2 absorbed from atmosphere This includes storing the "missing" fossil fuel CO2 from sentence 1! What We Now Know - Complete Picture: • Opening mystery: Missing CO2 from fossil fuels • Auclair's solution: Northern forests absorbed it • Historical shift: Forests changed from CO2 source to CO2 sink around 1920 • Mechanism: Tree growth exceeded losses from fires/logging • Timeline: 1920-1970 (50 years) of CO2 absorption Reading Strategy Insight: This is the satisfying conclusion that ties everything together! We started with missing CO2 and now know exactly where it went and when. The passage has come full circle. |
2. Passage Summary:
Author's Purpose:
To explain how a scientist solved the mystery of missing carbon dioxide by showing that northern forests changed from releasing CO2 to absorbing it.
Summary of Passage Structure:
In this passage, the author walks us through how a scientific puzzle was solved step by step:
- First, the author presents a scientific mystery - CO2 levels aren't as high as expected based on fossil fuel burning, so some CO2 is missing.
- Next, the author introduces scientist Allen Auclair's solution - northern forests have been absorbing the missing CO2 and storing it as wood.
- Then, the author explains Auclair's research method and key discovery that forests switched from being CO2 sources to CO2 sinks over time.
- Finally, the author provides the complete timeline showing how forests released CO2 before 1890 due to fires and logging, but after 1920 began absorbing CO2 because tree growth outpaced forest losses.
Main Point:
Northern forests have been absorbing the missing carbon dioxide from fossil fuels because around 1920, tree growth rates increased so much that forests switched from releasing CO2 to storing it, which accounts for why atmospheric CO2 levels are lower than scientists expected.
3. Question Analysis:
This question asks us to identify the primary concern or main purpose of the passage. We need to understand what the author is fundamentally trying to accomplish - whether they're explaining something, arguing against something, evaluating something, or presenting information in some other way.
Connecting to Our Passage Analysis:
Our passage analysis reveals a clear structure that starts with a scientific puzzle and walks through its solution:
- Opening mystery established: "Atmospheric carbon dioxide (CO2) has been increasing since 1700, but the amount of CO2 produced in that time by burning fossil fuels should have resulted in a much greater increase than has been observed."
- Proposed solution introduced: Auclair's theory that northern forests have been absorbing the missing CO2
- Evidence and methodology presented: How Auclair measured forest gains vs. losses to support his theory
- Complete explanation provided: The historical timeline showing how forests switched from CO2 sources to CO2 sinks
The passage analysis shows this is fundamentally about solving a scientific puzzle - explaining where missing CO2 went.
Prethinking:
The passage starts with a puzzling discrepancy (CO2 levels lower than expected) and then systematically explains how Auclair solved this puzzle by showing that northern forests absorbed the missing carbon. The author's primary purpose is to walk us through this explanation of a previously mysterious phenomenon. This suggests we need an answer choice about explaining or providing a solution to something puzzling or unexpected.
Why It's Wrong:
- The passage doesn't argue against or disprove any existing claim about CO2 causes
- Instead, it presents Auclair's research as providing a solution, not refuting other theories
- The tone is explanatory and supportive of Auclair's findings, not argumentative
Common Student Mistakes:
- Did the author argue against the idea that fossil fuels cause CO2 increases?
→ No, the passage accepts that fossil fuels increase CO2 but explains why the increase is smaller than expected - Is presenting a solution the same as refuting other claims?
→ No, explaining where missing CO2 went is different from arguing against existing theories
Why It's Wrong:
- The passage focuses on a specific research finding, not a "common natural process"
- The forest carbon absorption described is presented as a particular phenomenon studied by Auclair, not a general natural process
- The emphasis is on solving the missing CO2 mystery, not analyzing routine forest behavior
Common Student Mistakes:
- Isn't forest carbon absorption a natural process?
→ Yes, but the passage treats it as the solution to a specific puzzle, not as analysis of a common process - Does "analysis" mean the same as "explanation"?
→ Not quite - analysis suggests examining a known process, while this passage explains an unexpected discovery
Why It's Right:
- The passage opens with a clear puzzle: CO2 levels are lower than expected based on fossil fuel burning
- The entire structure moves from mystery (missing CO2) to solution (forest absorption)
- Auclair's research provides the explanation for this puzzling discrepancy
- The timeline and evidence all serve to explain why this unexpected phenomenon occurred
Key Evidence: "Atmospheric carbon dioxide (CO2) has been increasing since 1700, but the amount of CO2 produced in that time by burning fossil fuels should have resulted in a much greater increase than has been observed."
Why It's Wrong:
- The passage presents Auclair's methodology but doesn't critique or evaluate whether his methods are sound
- The author describes his approach neutrally without judgment about its effectiveness
- The focus is on what Auclair discovered, not on assessing how he discovered it
Common Student Mistakes:
- Since the passage mentions Auclair's measurements and methods, isn't it evaluating his methodology?
→ No, describing methodology is different from evaluating it - the passage explains what he did, not whether it was good science - Does presenting research findings count as evaluation?
→ No, the passage reports his conclusions without critical assessment
Why It's Wrong:
- The passage presents only one explanation (Auclair's forest absorption theory), not two competing explanations
- There's no contrast between different theories or approaches to explaining the missing CO2
- The structure is problem-solution, not explanation vs. explanation
Common Student Mistakes:
- Doesn't the passage contrast forests as CO2 sources versus CO2 sinks?
→ That's a historical timeline within Auclair's single explanation, not two separate explanations of the phenomenon - Are the before-1890 and after-1920 periods two different explanations?
→ No, they're parts of one comprehensive explanation showing how forests changed over time