ACT Science: Conflicting Viewpoints (Drill 5)

Question 1. Which of the following does Scientist 1 cite as the primary evidence that orbital cycles drive glacial periods?

• A) Climate records show cyclical variability at periods that match the three Milankovitch frequencies precisely ✓
• B) CO₂ concentrations were approximately 100 ppm lower during glacial maxima than during interglacials in the data presented
• C) Each doubling of CO₂ concentration produces a warming of approximately 3°C
• D) Ice-albedo feedback amplifies the initial cooling caused by CO₂ reduction

Explanation: Scientist 1 states: "Spectral analysis of climate records preserved in deep-sea sediments and ice cores reveals cyclical climate variability at periods of approximately 100,000, 41,000, and 23,000 years -- matching precisely the three Milankovitch frequencies." This pattern match between orbital periods and observed climate cycles is the central evidence for Milankovitch forcing. Option B states a fact both scientists acknowledge but is not Scientist 1's primary argument for orbital driving. Option C is Scientist 2's statement about CO₂ radiative forcing. Option D describes a feedback that Scientist 2 invokes in support of CO₂ forcing.

Question 2. Which of the following statements would both Scientist 1 and Scientist 2 most likely accept as accurate?

• A) Milankovitch orbital cycles alone are sufficient to explain the full 4 to 7°C temperature difference between glacial and interglacial periods
• B) CO₂ is the initial trigger of glacial cycles and orbital changes play no role
• C) CO₂ concentrations in the atmosphere were lower during glacial periods than during interglacial periods ✓
• D) Ice-albedo feedback is the primary driver of glacial cycles and operates independently of both CO₂ and orbital changes

Explanation: The intro paragraph establishes as agreed background: "CO₂ concentrations ranged from approximately 180 ppm during glacial maxima to approximately 280 ppm during interglacials." Both scientists build their arguments around this observed CO₂ variation -- Scientist 1 treats it as a consequence of orbital-driven temperature change, while Scientist 2 treats it as the primary cause. Both accept the empirical fact that CO₂ was lower during glacials. Option A is contradicted by Scientist 2, who explicitly states Milankovitch forcing "is too small without the powerful amplification provided by CO₂." Option B is contradicted by Scientist 1 and overstates Scientist 2's position (S2 says orbital cycles "provide a background rhythm"). Option D is not proposed by either scientist -- both treat ice-albedo as a feedback, not a primary driver.

Question 3. Which of the following findings, if confirmed, would most weaken Scientist 1's hypothesis?

• A) Ice core records from multiple sites all show CO₂ and temperature rising and falling together across glacial cycles
• B) Among the three Milankovitch cycles, the eccentricity cycle (~100,000 years) produces the smallest change in total solar energy received by Earth, yet corresponds to the dominant and strongest glacial rhythm in recent Earth history ✓
• C) Ice-albedo feedback amplifies the initial cooling or warming caused by orbital forcing
• D) The obliquity cycle of ~41,000 years dominated glacial pacing before approximately 1 million years ago

Explanation: Scientist 1's hypothesis requires that orbital forcing drives glacial cycles. The eccentricity cycle (~100,000 years) produces a very small change in total solar insolation -- far smaller than the obliquity or precession cycles -- yet the 100,000-year cycle is the dominant feature of the glacial record over the past 800,000 years. This mismatch -- the weakest orbital forcing producing the strongest climate response -- is a genuine challenge to pure Milankovitch forcing and suggests that another amplifier (such as CO₂) must be primarily responsible for the magnitude and timing of glacial cycles. Option A shows CO₂-temperature correlation, which Scientist 1 already acknowledges and interprets as CO₂ being a feedback, not a weakness. Option C describes ice-albedo feedback, which Scientist 1 could incorporate into an orbital forcing model. Option D actually supports Milankovitch theory by showing a different orbital cycle (obliquity) dominated at a different time, consistent with changing orbital configurations.

Question 4. Scientist 2 argues that CO₂ is the primary driver of glacial cycles. This argument assumes which of the following?

• A) Earth's orbital geometry does not change over the timescales relevant to glacial cycles
• B) CO₂ concentrations were identical during all glacial periods regardless of orbital configuration
• C) A greenhouse gas can function as the primary driver of a climate cycle even if its atmospheric concentration initially changes in response to temperature rather than causing the temperature change ✓
• D) Ice-albedo feedback operates only when CO₂ concentrations are below 200 ppm

Explanation: High-precision ice core analyses show that temperature begins rising approximately 800 years before CO₂ concentrations increase at each glacial termination. This means CO₂ initially responds to warming (likely released from the ocean as it warms) rather than triggering it. For Scientist 2's CO₂-as-primary-driver hypothesis to hold despite this timing, Scientist 2 must assume that even if CO₂ initially responds to temperature, it can still amplify and sustain the cycle powerfully enough to be considered the dominant causal factor -- in other words, that being an initial feedback does not disqualify CO₂ from being the primary driver. Option A is false and contradicted by both scientists, who acknowledge Milankovitch cycles exist. Option B is not claimed and would be false. Option D introduces a specific threshold not stated or implied by either scientist.

Question 5. High-precision analysis of an Antarctic ice core reveals that at each of the last eight glacial terminations, Antarctic temperature began rising approximately 800 years before atmospheric CO₂ concentrations increased. This finding most strongly supports the hypothesis of:

• A) Scientist 1 only, because the temperature increase precedes the CO₂ increase, suggesting CO₂ is responding to an earlier warming trigger rather than causing it ✓
• B) Scientist 2 only, because the close timing of temperature and CO₂ confirms that CO₂ is driving temperature
• C) Both scientists equally, because both predict a tight correlation between CO₂ and temperature
• D) Neither scientist, because neither hypothesis makes a prediction about the relative timing of temperature and CO₂ changes

Explanation: If temperature rises approximately 800 years before CO₂ at every glacial termination, then CO₂ cannot be the initial trigger of warming -- something else must warm the planet first, and CO₂ then rises in response (likely as oceans warm and release dissolved CO₂). This is precisely what Scientist 1 predicts: orbital changes drive initial warming, and CO₂ "acts as an amplifying feedback rather than the initial trigger." This temporal ordering supports Scientist 1's causal framework. Scientist 2's hypothesis that CO₂ drives temperature is directly challenged -- if CO₂ comes after temperature, it could not have caused the temperature rise that preceded it. Option B misrepresents the finding: a lag of CO₂ behind temperature is the opposite of what a CO₂-driven hypothesis predicts. Option C is wrong because the finding specifically addresses the causal order, where the two scientists differ.