📘 IAS Prelims 2025 — GS-I Q.27 | Classroom Explanation

📌 Question

Q.27) Consider the following statements:

Statement I: In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing the landmasses, and poleward while crossing the oceans.

Statement II: In January, the air over the oceans is warmer than that over the landmasses in the Northern Hemisphere.

Which one of the following is correct in respect of the above statements?

(a) Both Statement I and Statement II are correct and Statement II explains Statement I
(b) Both Statement I and Statement II are correct but Statement II does not explain Statement I
(c) Statement I is correct but Statement II is not correct
(d) Statement I is not correct but Statement II is correct

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✅ Correct Answer: (a)

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🧑‍🏫 Classroom Explanation

This question tests understanding of seasonal temperature distribution and land–sea contrast, a classic topic in climatology frequently used by UPSC to test cause–effect reasoning.

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🔍 Key Concept: Isotherms and Land–Sea Contrast

• Isotherms are lines joining places of equal temperature
• Generally, they run parallel to latitudes
• However, deviations occur due to:

• Land–sea contrast
• Ocean currents
• Seasonal changes

These deviations are more pronounced in January than in July, especially in the Northern Hemisphere.

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🔍 Statement-wise Analysis

✅ Statement I: Correct

• In January (winter in Northern Hemisphere):

• Land cools rapidly
• Oceans retain heat longer

• As a result:

• Isotherms bend equatorward (southward) over cold landmasses
• Isotherms bend poleward (northward) over relatively warmer oceans

➡️ Hence, Statement I is correct.

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✅ Statement II: Correct

• Water has higher specific heat than land
• Oceans lose heat slowly compared to land
• Therefore, in January:

• Air over oceans is warmer than air over land at the same latitude

➡️ Hence, Statement II is correct.

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🔗 Cause–Effect Link (UPSC Logic)

• Warmer oceans → higher temperatures over oceans
• Colder land → lower temperatures over continents
• This temperature contrast directly causes:

• Poleward bending of isotherms over oceans
• Equatorward bending over land

➡️ Statement II correctly explains Statement I

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🧮 Logical Elimination (UPSC Style)

• Statement I → True
• Statement II → True
• Statement II explains Statement I → Yes

➡️ Correct option: (a)

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🎯 Final Answer

✅ Correct Answer: (a)

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📦 Info Box — Extra Points (Prelims Value Add)

• January deviations are strongest in:

• Northern Hemisphere (larger landmass)
  • July shows the reverse pattern:
• Land warmer than oceans
• Isotherms bend poleward over land and equatorward over oceans

• Gulf Stream and North Atlantic Drift:

• Keep Western Europe warmer than corresponding latitudes in North America
• Classic example of ocean-current impact on isotherms

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🔗 Bridge Points (Future Questions)

• Specific heat of land vs water
• Seasonal inversion of pressure and temperature
• Ocean currents and climate moderation

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📍 GS Mapping

GS Paper I
Subject: Geography
Theme: Climatology — Temperature Distribution
Nature: Conceptual + Cause–Effect Reasoning

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