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21 Aug 2025, 21:39
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Scientists have speculated about how volcanoes influence climate since the early 1900s, yet only after satellite sensors became routine in the 1990s did they confirm that large eruptions can loft vast plumes of sulfur dioxide (SO₂) into the stratosphere. There the gas oxidizes into sulfate aerosols that brighten Earth’s albedo, reflecting a fraction of incoming sunlight and lowering surface temperatures for one to three years. Balloon observations after Krakatoa in 1883 and after El Chichón in 1982 hinted at this link, but the evidence was fragmentary and often disputed. Today researchers label this sunlight-blocking mechanism volcanic forcing.
The benchmark case is the 1991 eruption of Mount Pinatubo in the Philippines. Pinatubo hurled roughly 20 million tons of SO₂ well above the tropopause, and, carried by fast stratospheric winds, the resulting aerosol veil circled the globe within weeks. Its peak aerosol optical depth reached about 0.15, values once cited in early nuclear-winter simulations, and global mean temperature fell by nearly 0.5 degrees Celsius over the next two years. The episode persuaded many climatologists that any eruption of comparable size would deliver a predictable, though temporary, planetary chill.
That expectation faltered in 2010 when Iceland’s Eyjafjallajökull volcano, famous for grounding trans-Atlantic flights, released millions of tons of SO₂ yet produced virtually no measurable cooling. Detailed lidar and aircraft surveys showed that most of the plume topped out near nine kilometres, below the eleven-to-seventeen kilometre band where stratospheric circulation accelerates, so aerosols settled out within months and remained confined to the North Atlantic basin.
The 2014 Holuhraun fissure, also in Iceland, deepened the puzzle. Although Holuhraun emitted even more SO₂ than Eyjafjallajökull, reanalysis data recorded only a faint minus 0.07 degree Celsius signal. Together the two Icelandic events underscored that latitude and plume height can outweigh sheer emission volume; high-latitude eruptions often vent below the altitude needed for long-lived, planet-circling aerosol layers.
Accumulating data now support a refined pattern. Tropical eruptions such as Pinatubo or El Chichón inject SO₂ directly into swift equatorial circulation, spreading aerosols worldwide, whereas most high-latitude eruptions remain regionally bottled and short lived. Current climate models therefore couple plume-height dynamics with aerosol chemistry, water-vapour interactions, and circulation thresholds to predict which future eruptions will matter for global forecasts and which will be climatic footnotes. Clarifying those thresholds is increasingly crucial for risk assessments of geoengineering proposals that would deliberately mimic volcanic injections.
Which of the following most accurately describes how the passage is organized?
A. A hypothesis is presented, supporting data are reviewed, and a call for additional research is issued to strengthen the hypothesis.
B. A phenomenon is described, a prediction about its effects is offered, and evidence contradicting that prediction is analyzed.
C. Two competing explanations for a phenomenon are proposed, and one is rejected on the basis of empirical data.
D. A theory is outlined, and an example fully consistent with the theory’s predictions is examined in detail.
E. A well-known phenomenon is outlined, an event that appears inconsistent with it is examined, and the original explanation is refined to accommodate that event.
The benchmark case is the 1991 eruption of Mount Pinatubo in the Philippines. Pinatubo hurled roughly 20 million tons of SO₂ well above the tropopause, and, carried by fast stratospheric winds, the resulting aerosol veil circled the globe within weeks. Its peak aerosol optical depth reached about 0.15, values once cited in early nuclear-winter simulations, and global mean temperature fell by nearly 0.5 degrees Celsius over the next two years. The episode persuaded many climatologists that any eruption of comparable size would deliver a predictable, though temporary, planetary chill.
That expectation faltered in 2010 when Iceland’s Eyjafjallajökull volcano, famous for grounding trans-Atlantic flights, released millions of tons of SO₂ yet produced virtually no measurable cooling. Detailed lidar and aircraft surveys showed that most of the plume topped out near nine kilometres, below the eleven-to-seventeen kilometre band where stratospheric circulation accelerates, so aerosols settled out within months and remained confined to the North Atlantic basin.
The 2014 Holuhraun fissure, also in Iceland, deepened the puzzle. Although Holuhraun emitted even more SO₂ than Eyjafjallajökull, reanalysis data recorded only a faint minus 0.07 degree Celsius signal. Together the two Icelandic events underscored that latitude and plume height can outweigh sheer emission volume; high-latitude eruptions often vent below the altitude needed for long-lived, planet-circling aerosol layers.
Accumulating data now support a refined pattern. Tropical eruptions such as Pinatubo or El Chichón inject SO₂ directly into swift equatorial circulation, spreading aerosols worldwide, whereas most high-latitude eruptions remain regionally bottled and short lived. Current climate models therefore couple plume-height dynamics with aerosol chemistry, water-vapour interactions, and circulation thresholds to predict which future eruptions will matter for global forecasts and which will be climatic footnotes. Clarifying those thresholds is increasingly crucial for risk assessments of geoengineering proposals that would deliberately mimic volcanic injections.
Which of the following most accurately describes how the passage is organized?
A. A hypothesis is presented, supporting data are reviewed, and a call for additional research is issued to strengthen the hypothesis.
B. A phenomenon is described, a prediction about its effects is offered, and evidence contradicting that prediction is analyzed.
C. Two competing explanations for a phenomenon are proposed, and one is rejected on the basis of empirical data.
D. A theory is outlined, and an example fully consistent with the theory’s predictions is examined in detail.
E. A well-known phenomenon is outlined, an event that appears inconsistent with it is examined, and the original explanation is refined to accommodate that event.
21 Aug 2025, 21:39
Kudos
Bookmarks
Official Solution:
Scientists have speculated about how volcanoes influence climate since the early 1900s, yet only after satellite sensors became routine in the 1990s did they confirm that large eruptions can loft vast plumes of sulfur dioxide (SO₂) into the stratosphere. There the gas oxidizes into sulfate aerosols that brighten Earth’s albedo, reflecting a fraction of incoming sunlight and lowering surface temperatures for one to three years. Balloon observations after Krakatoa in 1883 and after El Chichón in 1982 hinted at this link, but the evidence was fragmentary and often disputed. Today researchers label this sunlight-blocking mechanism volcanic forcing.
The benchmark case is the 1991 eruption of Mount Pinatubo in the Philippines. Pinatubo hurled roughly 20 million tons of SO₂ well above the tropopause, and, carried by fast stratospheric winds, the resulting aerosol veil circled the globe within weeks. Its peak aerosol optical depth reached about 0.15, values once cited in early nuclear-winter simulations, and global mean temperature fell by nearly 0.5 degrees Celsius over the next two years. The episode persuaded many climatologists that any eruption of comparable size would deliver a predictable, though temporary, planetary chill.
That expectation faltered in 2010 when Iceland’s Eyjafjallajökull volcano, famous for grounding trans-Atlantic flights, released millions of tons of SO₂ yet produced virtually no measurable cooling. Detailed lidar and aircraft surveys showed that most of the plume topped out near nine kilometres, below the eleven-to-seventeen kilometre band where stratospheric circulation accelerates, so aerosols settled out within months and remained confined to the North Atlantic basin.
The 2014 Holuhraun fissure, also in Iceland, deepened the puzzle. Although Holuhraun emitted even more SO₂ than Eyjafjallajökull, reanalysis data recorded only a faint minus 0.07 degree Celsius signal. Together the two Icelandic events underscored that latitude and plume height can outweigh sheer emission volume; high-latitude eruptions often vent below the altitude needed for long-lived, planet-circling aerosol layers.
Accumulating data now support a refined pattern. Tropical eruptions such as Pinatubo or El Chichón inject SO₂ directly into swift equatorial circulation, spreading aerosols worldwide, whereas most high-latitude eruptions remain regionally bottled and short lived. Current climate models therefore couple plume-height dynamics with aerosol chemistry, water-vapour interactions, and circulation thresholds to predict which future eruptions will matter for global forecasts and which will be climatic footnotes. Clarifying those thresholds is increasingly crucial for risk assessments of geoengineering proposals that would deliberately mimic volcanic injections.
Which of the following most accurately describes how the passage is organized?
A. A hypothesis is presented, supporting data are reviewed, and a call for additional research is issued to strengthen the hypothesis.
B. A phenomenon is described, a prediction about its effects is offered, and evidence contradicting that prediction is analyzed.
C. Two competing explanations for a phenomenon are proposed, and one is rejected on the basis of empirical data.
D. A theory is outlined, and an example fully consistent with the theory’s predictions is examined in detail.
E. A well-known phenomenon is outlined, an event that appears inconsistent with it is examined, and the original explanation is refined to accommodate that event.
A) Incorrect. The passage does start with the idea that volcanic eruptions cool the planet, yet it quickly shows that this idea on its own does not cover all cases. The two Icelandic eruptions weaken the original rule instead of confirming it. When the author says “clarifying those thresholds is crucial,” he is not simply calling for more research to back the old view. He is saying the view must be updated because new evidence has changed the picture.
B) Incorrect. The text does present a prediction: large sulfur-rich eruptions should cool Earth. The Icelandic eruptions seem to break that rule. Still, the author does more than point out the mismatch. He explains in straightforward terms that plume height and latitude are key factors. The revised rule now covers both cooling events, such as Pinatubo, and non-cooling events, such as the Icelandic eruptions. Option B stops before this update and therefore skips a critical step in the passage.
C) Incorrect. The author never places two rival theories side by side. He begins with one explanation, observes data that do not fit, and then adjusts that same explanation by adding altitude and latitude limits. No second theory is introduced or rejected, so the pattern described in option C does not match.
D) Incorrect. Mount Pinatubo does illustrate the early theory perfectly, but the passage also includes counter-examples that force a revision. Because the text pairs the confirming case with evidence that demands an update, option D leaves out half of the story.
E) Correct. First, the passage explains volcanic forcing and uses Pinatubo as the classic example. Next, it examines two Icelandic eruptions that do not cause the expected cooling. Finally, the author refines the original idea, adding plume height and latitude so the rule now accommodates both cooling and non-cooling events. The sequence is rule, apparent exception, and improved rule, which aligns with option E.
Answer: E
Scientists have speculated about how volcanoes influence climate since the early 1900s, yet only after satellite sensors became routine in the 1990s did they confirm that large eruptions can loft vast plumes of sulfur dioxide (SO₂) into the stratosphere. There the gas oxidizes into sulfate aerosols that brighten Earth’s albedo, reflecting a fraction of incoming sunlight and lowering surface temperatures for one to three years. Balloon observations after Krakatoa in 1883 and after El Chichón in 1982 hinted at this link, but the evidence was fragmentary and often disputed. Today researchers label this sunlight-blocking mechanism volcanic forcing.
The benchmark case is the 1991 eruption of Mount Pinatubo in the Philippines. Pinatubo hurled roughly 20 million tons of SO₂ well above the tropopause, and, carried by fast stratospheric winds, the resulting aerosol veil circled the globe within weeks. Its peak aerosol optical depth reached about 0.15, values once cited in early nuclear-winter simulations, and global mean temperature fell by nearly 0.5 degrees Celsius over the next two years. The episode persuaded many climatologists that any eruption of comparable size would deliver a predictable, though temporary, planetary chill.
That expectation faltered in 2010 when Iceland’s Eyjafjallajökull volcano, famous for grounding trans-Atlantic flights, released millions of tons of SO₂ yet produced virtually no measurable cooling. Detailed lidar and aircraft surveys showed that most of the plume topped out near nine kilometres, below the eleven-to-seventeen kilometre band where stratospheric circulation accelerates, so aerosols settled out within months and remained confined to the North Atlantic basin.
The 2014 Holuhraun fissure, also in Iceland, deepened the puzzle. Although Holuhraun emitted even more SO₂ than Eyjafjallajökull, reanalysis data recorded only a faint minus 0.07 degree Celsius signal. Together the two Icelandic events underscored that latitude and plume height can outweigh sheer emission volume; high-latitude eruptions often vent below the altitude needed for long-lived, planet-circling aerosol layers.
Accumulating data now support a refined pattern. Tropical eruptions such as Pinatubo or El Chichón inject SO₂ directly into swift equatorial circulation, spreading aerosols worldwide, whereas most high-latitude eruptions remain regionally bottled and short lived. Current climate models therefore couple plume-height dynamics with aerosol chemistry, water-vapour interactions, and circulation thresholds to predict which future eruptions will matter for global forecasts and which will be climatic footnotes. Clarifying those thresholds is increasingly crucial for risk assessments of geoengineering proposals that would deliberately mimic volcanic injections.
Which of the following most accurately describes how the passage is organized?
A. A hypothesis is presented, supporting data are reviewed, and a call for additional research is issued to strengthen the hypothesis.
B. A phenomenon is described, a prediction about its effects is offered, and evidence contradicting that prediction is analyzed.
C. Two competing explanations for a phenomenon are proposed, and one is rejected on the basis of empirical data.
D. A theory is outlined, and an example fully consistent with the theory’s predictions is examined in detail.
E. A well-known phenomenon is outlined, an event that appears inconsistent with it is examined, and the original explanation is refined to accommodate that event.
A) Incorrect. The passage does start with the idea that volcanic eruptions cool the planet, yet it quickly shows that this idea on its own does not cover all cases. The two Icelandic eruptions weaken the original rule instead of confirming it. When the author says “clarifying those thresholds is crucial,” he is not simply calling for more research to back the old view. He is saying the view must be updated because new evidence has changed the picture.
B) Incorrect. The text does present a prediction: large sulfur-rich eruptions should cool Earth. The Icelandic eruptions seem to break that rule. Still, the author does more than point out the mismatch. He explains in straightforward terms that plume height and latitude are key factors. The revised rule now covers both cooling events, such as Pinatubo, and non-cooling events, such as the Icelandic eruptions. Option B stops before this update and therefore skips a critical step in the passage.
C) Incorrect. The author never places two rival theories side by side. He begins with one explanation, observes data that do not fit, and then adjusts that same explanation by adding altitude and latitude limits. No second theory is introduced or rejected, so the pattern described in option C does not match.
D) Incorrect. Mount Pinatubo does illustrate the early theory perfectly, but the passage also includes counter-examples that force a revision. Because the text pairs the confirming case with evidence that demands an update, option D leaves out half of the story.
E) Correct. First, the passage explains volcanic forcing and uses Pinatubo as the classic example. Next, it examines two Icelandic eruptions that do not cause the expected cooling. Finally, the author refines the original idea, adding plume height and latitude so the rule now accommodates both cooling and non-cooling events. The sequence is rule, apparent exception, and improved rule, which aligns with option E.
Answer: E
09 Oct 2025, 07:36
Kudos
Bookmarks
I did not quite understand the solution. Not sure why b is not the answer
