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 levels have gone up since 1700, but surprisingly less than we'd expect given fossil fuel burning. What it does: Introduces a puzzle/mystery - sets up the central problem Source/Type: Factual observation Connection to Previous Sentences: First sentence - establishes the foundation Visualization: Expected CO2 increase from fossil fuels: 150 units Actual observed increase: 80 units Missing CO2: 70 units - Where did it go? What We Know So Far: There's missing CO2 What We Don't Know Yet: Where the missing CO2 went Reading Strategy Insight: This is classic RC setup - identify the mystery that the passage will solve |
| 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 believes northern forests are absorbing the missing CO2 and converting it to wood. What it does: Provides the proposed solution to the mystery Source/Type: Researcher's claim/hypothesis Connection to Previous Sentences: - Sentence 1 told us: CO2 is missing - NOW Sentence 2: Auclair's theory explains where it went - This directly answers the puzzle from sentence 1! Visualization: Missing 70 units of CO2 → Northern forests → Converted to wood What We Know So Far: Missing CO2 + Auclair's theory it went into forest wood What We Don't Know Yet: How Auclair proves this theory Reading Strategy Insight: Feel confident here - we now have both problem and proposed solution. Expect the rest to support this theory. |
| 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 measures forest factors and tree growth to show that faster tree growth since 1920 created enough wood to explain 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: - Sentence 2 told us: Auclair's theory (forests absorb CO2) - NOW Sentence 3: HOW he proves it (measuring growth rates) - This builds on sentence 2 by providing evidence Visualization: 1920: Normal tree growth rate = 2 units/year 1970: Faster tree growth rate = 5 units/year Extra wood created = 3 units/year × 50 years = 150 units This 150 units accounts for the missing 70 units of CO2 What We Know So Far: Problem + Theory + Evidence method + Key timeframe (since 1920) What We Don't Know Yet: Specific details of how forests changed over time Reading Strategy Insight: This is still supporting the same basic idea - no new complexity, just more detail on the same theory |
| 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 absorb or release carbon, you compare wood gained vs. wood lost. What it does: Explains the basic logic of the analysis Source/Type: Methodological explanation Connection to Previous Sentences: - Previous sentences described Auclair's complex measurements - NOW: This simplifies the concept - it's just addition vs. subtraction! - This is NOT new information, it's clarification Visualization: Wood Added (from growth): 200 units Wood Lost (from fires, logging): 150 units Net Result: +50 units = Carbon sink If reversed: Net Result: -50 units = Carbon source Reading Strategy Insight: Feel relieved here - this is simplification, not new complexity. The author is helping you understand the basic math. |
| 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 carbon to absorbing it. What it does: States the main conclusion/finding Source/Type: Research conclusion Connection to Previous Sentences: - Sentence 4 explained: the basic method (compare gains vs. losses) - NOW Sentence 5: The actual result when Auclair did this comparison - This directly applies the method to get a conclusion Visualization: 1800s: Forests = Carbon Source (releasing CO2) 1900s: Forests = Carbon Sink (absorbing CO2) Timeline: Source → transition → Sink What We Know So Far: Complete theory with conclusion - forests changed from source to sink What We Don't Know Yet: Specific details about the timeline of this change Reading Strategy Insight: This is the payoff - we now have the complete answer to the original mystery. |
| 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. | What it says: Pre-1890, forests released CO2 due to fires and logging, which made forest debris rot faster. What it does: Provides specific details about the "carbon source" period Source/Type: Research findings with scientific explanation Connection to Previous Sentences: - Sentence 5 told us: forests changed from source to sink - NOW Sentences 6-7: Details about the "source" period - This elaborates on something we already know, doesn't contradict it Visualization: Before 1890: Logging + Fires → Trees cleared → Forest floor debris exposed → Faster rotting → CO2 released Net effect: Forests release more CO2 than they absorb Reading Strategy Insight: This is supportive detail, not new argument. We're getting the "why" behind what we already learned. |
| 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: Post-1920, faster tree growth exceeded fire/logging losses, making forests absorb CO2 for 50 years. What it does: Provides specific details about the "carbon sink" period and completes the timeline Source/Type: Research findings Connection to Previous Sentences: - Previous sentences: Details about "source" period (pre-1890) - NOW: Details about "sink" period (post-1920) - This completes the before/after comparison and restates the main conclusion Visualization: After 1920: Tree growth: +500 units/year Fire + logging losses: -300 units/year Net: +200 units/year absorbed = Carbon sink Over 50 years: 200 × 50 = 10,000 units of CO2 stored What We Know So Far: Complete story with timeline and explanation Reading Strategy Insight: This final sentence ties everything together and confirms our understanding. The passage has come full circle from mystery to complete explanation. |
2. Passage Summary:
Author's Purpose:
To explain how a scientific mystery about missing atmospheric carbon dioxide was solved by showing that northern forests changed from releasing carbon to absorbing it.
Summary of Passage Structure:
In this passage, the author walks us through a clear problem-and-solution structure:
- First, the author presents a puzzle - atmospheric CO2 levels haven't increased as much as expected given all the fossil fuel burning since 1700.
- Next, the author introduces a scientist's theory that solves this mystery - Allen Auclair claims that northern forests have been absorbing the missing carbon and turning it into wood.
- Then, the author explains how Auclair proved his theory by measuring forest factors and tree growth rates, showing that the basic method is simply comparing wood gained versus wood lost.
- Finally, the author provides the specific timeline and details of Auclair's findings, showing how forests switched from being carbon sources before 1890 to carbon sinks after 1920.
Main Point:
Northern hemisphere forests have been acting like giant sponges for carbon dioxide - they used to release more carbon than they absorbed (mainly due to logging and fires), but since 1920, faster tree growth has made them absorb more carbon than they release, which explains where much of the "missing" CO2 from fossil fuel burning has gone.
3. Question Analysis:
This is a primary purpose question asking what the passage as a whole is "primarily concerned" with. I need to identify the main function or goal of the entire passage, not just individual details or sections.
Connecting to Our Passage Analysis:
From our passage analysis, the structure is crystal clear:
- Mystery introduced: CO2 levels haven't increased as much as expected from fossil fuel burning
- Solution proposed: Auclair's theory that northern forests are absorbing the missing carbon
- Evidence provided: Details of Auclair's methodology and findings
- Timeline explained: How forests changed from carbon sources to carbon sinks
The passage analysis shows this follows a classic "problem-and-solution" structure where the author presents a puzzling phenomenon (missing CO2) and then walks through a scientist's explanation for solving that puzzle.
Prethinking:
Based on the passage structure, the primary concern is explaining where the "missing" atmospheric CO2 went. The passage starts with a puzzle - CO2 should be higher given fossil fuel burning - and then systematically explains Auclair's solution. This is fundamentally about providing an explanation for something that seemed contradictory or puzzling. The correct answer should capture this explanatory purpose focused on solving a mystery.
Why It's Wrong:
- The passage doesn't refute any claim - it actually supports and explains Auclair's theory
- No opposing viewpoint is presented or argued against
- The focus is on explaining a phenomenon, not arguing against an existing explanation
Common Student Mistakes:
- Does the passage argue against the idea that fossil fuels cause CO2 increases?
→ No, it accepts that fossil fuels increase CO2 but explains why the increase isn't as large as expected - Is Auclair's work presented as controversial or disputed?
→ No, the passage presents his findings as explanatory, not as disagreement with other theories
Why It's Wrong:
- While carbon absorption by forests is natural, this isn't described as a "common" process
- The focus isn't on explaining how forests normally work, but on solving a specific CO2 puzzle
- The emphasis is on the surprising change from carbon source to sink, not routine forest processes
Common Student Mistakes:
- Isn't carbon absorption by trees a natural process?
→ Yes, but the passage focuses on the specific puzzle of missing atmospheric CO2, not general forest ecology - Does the passage explain how forests typically function?
→ No, it explains how northern forests specifically solved the CO2 mystery through an unusual historical change
Why It's Right:
- The passage begins with a clear puzzle: CO2 levels are lower than expected given fossil fuel burning
- It then systematically provides Auclair's explanation for this puzzling discrepancy
- The entire structure moves from "mystery" to "solution" with supporting evidence
- The phenomenon (lower than expected CO2) was genuinely puzzling to scientists
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 doesn't critique or evaluate Auclair's methodology
- No discussion of whether his methods are sound, flawed, or could be improved
- The methodology is presented as factual information, not subjected to evaluation
Common Student Mistakes:
- Doesn't the passage describe Auclair's research methods?
→ Yes, but describing methods isn't the same as evaluating their quality or validity - Are there any criticisms of how Auclair conducted his study?
→ No, the passage presents his approach and findings without any critical assessment
Why It's Wrong:
- Only one explanation is presented (Auclair's forest theory)
- No alternative explanations for the missing CO2 are discussed or contrasted
- The passage focuses on supporting one theory, not comparing multiple theories
Common Student Mistakes:
- Aren't there two time periods described (before 1890 vs. after 1920)?
→ Yes, but these are parts of the same explanation showing how forests changed over time - Does the passage mention different factors affecting forests?
→ Yes, but logging, fires, and growth are all components of Auclair's single unified explanation