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Geography · Temperature: Distribution & Controlling Factors

UPSC Prelims 2025, Question 27

The concept being tested: Differential land-ocean heating - isotherms bend equatorward over landmasses, poleward over oceans (Northern Hemisphere winter).

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?

Options

  1. ABoth Statement I and Statement II are correct and Statement II explains Statement ICorrect answer
  2. BBoth Statement I and Statement II are correct but Statement II does not explain Statement I
  3. CStatement I is correct but Statement II is not correct
  4. DStatement I is not correct but Statement II is correct

The answer: Both Statement I and Statement II are correct and Statement II explains Statement I

In January, the Northern Hemisphere is in winter. Land has a lower specific heat capacity than water, so it loses heat quickly and cools much faster than the oceans, which retain warmth because of their greater thermal capacity, vertical mixing, and warm currents such as the North Atlantic Drift. As a result, at any given latitude the ocean surface stays warmer than the adjoining landmass. Isotherms join points of equal temperature, so they must dip toward the equator wherever they cross land, staying on the colder surface, and swing poleward wherever they cross the ocean, staying on the warmer surface. This equatorward bend over land and poleward bend over oceans is a direct consequence of the ocean being warmer than the land in January. Statement II is therefore not just true alongside Statement I, it is the actual cause of the pattern described in Statement I.

What UPSC was testing

UPSC is testing the differential heating property of land and water through the standard January world isotherm map, and the two-statement format is designed to check whether the aspirant can see Statement II as the explanatory cause of Statement I rather than treating them as merely two separate true facts.

How often this comes up

This concept has appeared 7 times in UPSC Prelims General Studies Paper I between 2015 and 2025 — in 2019, 2022, 2023, 2024 and 2025.

The option-by-option autopsy for this question — why each of the other three is wrong, and which neighbouring concept each one was built from — is in the app.