UPSC Prelims 2023 Q64: Land-Sea Temperature Contrast — Explained
Consider the following statements:
Statement-I:
The temperature contrast between continents and oceans is greater during summer than in winter.
Statement-II:
The specific heat of water is more than that of land surface.
Which one of the following is correct in respect of the above statements?
- Both Statement-I and Statement-II are correct and Statement-II is the correct explanation for Statement-I
- Both Statement-I and Statement-II are correct and Statement-II is not the correct explanation for Statement-I
- Statement-I is correct but Statement-II is incorrect
- Statement-I is incorrect but Statement-II is correct
Answer: (d) Statement-I is incorrect but Statement-II is correct
Statement-wise explanation
- Statement-I: incorrect — The land–ocean temperature contrast is greater in winter, not in summer. In winter the big northern continents lose heat fast and get very cold. NCERT records a mean January temperature of about −20°C in Siberia along 60°E. Oceans at the same latitudes stay much milder, and the Gulf Stream and North Atlantic Drift keep the North Atlantic warm. NCERT notes that isotherms bend away from the lines of latitude more in January than in July, especially in the Northern Hemisphere, and that bending is the visible sign of a bigger land–sea contrast.
- Statement-II: correct — Water has a specific heat of about 4.18 J/g°C. That is roughly five times the value for dry soil and rock. So water needs far more energy to change its temperature, and it heats and cools slowly. Water also mixes and lets sunlight reach several metres down, which spreads heat through a thick layer. Land heats and cools only in a thin top layer. Statement-II is the real cause of the land–sea temperature contrast. It cannot explain Statement-I, though, because Statement-I is false.
How to eliminate
Statement-II is a basic physics fact you can accept with confidence: water has a high specific heat. That leaves only the options where Statement-II is correct, so the question comes down to Statement-I. Reason it out from that same fact. Land loses heat quickly, so continents become extremely cold in winter (Siberia, Canada), while oceans hold their summer heat and stay mild. The gap between the two is therefore largest in winter. In summer the land does get hotter than the sea, but not by as much as Siberia gets colder in January. Fact to remember: isotherms deviate most in January, in the Northern Hemisphere, and the world's largest annual temperature range (over 60°C) is in north-eastern Eurasia. Watch the trap here. The examiner pairs a true reason with a reversed claim, and a candidate who recognises the reason ticks 'both correct'. Test each statement on its own first.
Know more
Differential heating of land and water is one of the main controls on world temperature. Land heats and cools faster than water for several reasons:
| Property | Land | Water |
|---|---|---|
| Specific heat | Low (~0.8 J/g°C for dry soil) | High (~4.18 J/g°C) |
| Depth of heating | Thin surface layer (heat moves only by conduction) | Several metres (light penetrates, water mixes) |
| Movement | Fixed | Currents and mixing carry heat away |
| Evaporation | Limited | Large, and it uses up energy |
| Result | Large daily and annual temperature range | Small, even temperature range |
Continentality. The farther a place is from the sea, the larger its temperature range. NCERT gives an annual range of more than 60°C over north-eastern Eurasia, the largest anywhere. Over the oceans near the equator the range is only about 3°C.
Why winter shows the bigger contrast. The Northern Hemisphere has much more land. In January the continents fall far below freezing, while warm currents such as the Gulf Stream and North Atlantic Drift keep the nearby oceans mild. So isotherms bend south over the continents and north over the oceans. In July the land is warmer than the sea, but the gap is smaller. The Southern Hemisphere is mostly ocean, so its isotherms stay nearly parallel to the lines of latitude.
Effects to link up:
- Monsoons: the land heats faster than the sea in summer, which forms low pressure over land and pulls in moist winds from the sea.
- Land and sea breezes: the same process on a daily scale.
- Coastal places such as Mumbai have a much smaller annual range than inland places such as Delhi.
NCERT Concepts to Revise
- Differential heating of land and water: Both statements rest on how land and water differ in how fast they heat and cool across the seasons.
- Specific heat: Statement-II compares the specific heat of water and land, so you need to know exactly what this quantity measures.
- Terrestrial radiation: Continents lose heat in winter through long-wave terrestrial radiation, which helps you judge which season shows the larger contrast.