Climate and oceans: previous-year questions
53 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 24 of them came in the last five papers.
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Which of the following are the evidences of the phenomenon of continental drift?
- I. The belt of ancient rocks from Brazil coast matches with those from Western Africa.
- II. The gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side.
- III. The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere.
Select the correct answer using the code given below.
Answer (c) & explanation
All three are evidence for continental drift (c). Item I is right: the belt of ancient rocks on the coast of Brazil matches those of West Africa. Item II is right: Ghana's gold has no source rock in Ghana, but its source exists in the Brazil plateau, showing the two lands once lay side by side. Item III is right: India's Gondwana sediments have twins in six southern landmasses. So options (a), (b) and (d), which leave items out, fail.
Notice other proofs used by Alfred Wegener (1912): the "jig-saw fit" of coastlines, tillite from old glaciers, and fossils like Mesosaurus found on both sides of the Atlantic. His idea was later explained by sea-floor spreading and plate tectonics.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement I : The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions.
Statement II : Subtropical and temperate areas have less dry winds.
Which one of the following is correct in respect of the above statements?
Answer (c) & explanation
Statement I is correct, Statement II is wrong (c). Statement I is right: dust in the air is highest over the subtropical and temperate belts. Statement II is wrong, because it reverses the reason: these belts have more dry winds, not fewer, and those winds lift dust from deserts and dry land, such as the Sahara, Thar and Gobi. Near the equator, heavy rain washes dust out of the air, and in polar regions, ice and snow give little dust to lift. So options (a), (b) and (d) fail.
Notice why dust matters: it acts as hygroscopic nuclei around which water condenses into clouds and rain. It also scatters sunlight, giving red sunrises and sunsets. Saharan dust even feeds the Amazon with phosphorus.
Answer as per the official UPSC answer key.
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?
Answer (a) & explanation
Both are correct and Statement II explains Statement I (a). Statement II is right: in the northern winter (January), land loses heat fast, while the oceans stay warmer, because water heats and cools slowly. Statement I follows: a given temperature line, or isotherm, is pushed south (equatorward) over the cold land and north (poleward) over the warm ocean. Options (b), (c) and (d) miss this link.
Notice the reverse in July: land is hotter, so isotherms bend poleward over land. Warm currents like the Gulf Stream and North Atlantic Drift push isotherms further north, keeping Norway's ports ice-free. In the Southern Hemisphere, with more ocean, isotherms run fairly straight.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement I : In the context of effect of water on rocks, chalk is known as a very permeable rock whereas clay is known as quite an impermeable or least permeable rock.
Statement II : Chalk is porous and hence can absorb water.
Statement III : Clay is not at all porous.
Which one of the following is correct in respect of the above statements?
Answer (c) & explanation
Only Statement II is correct and it explains Statement I (c). Statement II is right: chalk is porous and its pores connect, so water soaks through it, making it permeable. Statement III is wrong: clay is actually very porous, often holding more water than chalk, but its pores are so tiny that water cannot pass through, which makes it impermeable. So only II explains I, and options (a), (b) and (d) fail.
Notice the key difference: porosity is how much space a rock has for water; permeability is how easily water flows through. Permeable rocks form aquifers that store groundwater, while clay layers act as aquicludes that trap water above or below them, as in artesian wells.
Porous and permeable are not the same. Clay holds water but will not let it through.
Answer as per the official UPSC answer key.
Consider the following statements :
- I. Without the atmosphere, temperature would be well below freezing point everywhere on the Earth’s surface.
- II. Heat absorbed and trapped by the atmosphere maintains our planet’s average temperature.
- III. Atmosphere’s gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.
Which of the statements given above are correct?
Answer (c) & explanation
All three statements are correct (c). Statement I is right: without its air, Earth would average about −18°C, instead of about 15°C now, so it would be below freezing everywhere. Statement II is right: the heat absorbed and trapped by the atmosphere keeps our average temperature. Statement III is right: gases such as water vapour, carbon dioxide and methane absorb the long-wave (infrared) radiation the surface gives off and send part of it back. This is the greenhouse effect. So options (a), (b) and (d) fail.
Notice the difference: the natural greenhouse effect makes life possible, but the enhanced greenhouse effect from burning fossil fuels causes global warming. Water vapour is the largest natural greenhouse gas.
Answer as per the official UPSC answer key.
With reference to the planet Earth, consider the following statements :
- I. Rain forests produce more oxygen than that produced by oceans.
- II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world’s oxygen.
- III. Well-oxygenated surface water contains several folds higher oxygen than that in atmospheric air.
Which of the statements given above is/are correct?
Answer (b) & explanation
Only statement II is correct (b). Statement II is right: about half of Earth's oxygen comes from the ocean, mostly from phytoplankton and photosynthetic bacteria such as Prochlorococcus. Statement I is wrong: so rainforests do not produce more oxygen than oceans; the Amazon also uses up most of what it makes. Statement III is wrong: even well-mixed surface water holds far less oxygen than air, only a few millilitres per litre against about 210 in air.
Notice the link to dead zones: warm water holds even less oxygen, and nutrient runoff from fertilisers causes algal blooms that strip it out, as in the Gulf of Mexico and the Arabian Sea. Ocean warming threatens these tiny oxygen makers.
Answer as per the official UPSC answer key.
Consider the following statements :
- I. Anadyr in Siberia and Nome in Alaska are a few kilometers from each other, but when people are waking up and getting set for breakfast in these cities, it would be different days.
- II. When it is Monday in Anadyr, it is Tuesday in Nome.
Which of the statements given above is/are correct?
Answer (a) & explanation
Only statement I is correct (a). Statement I is right: the International Date Line runs through the Bering Strait between Anadyr in Siberia and Nome in Alaska, so at breakfast time the two places are on different days. Statement II is wrong: Anadyr, on the western (Asian) side, is a day ahead. So when it is Monday in Anadyr, it is still Sunday in Nome, not Tuesday. So options (b), (c) and (d) fail.
Notice the rule: crossing the Date Line westward, you add a day; crossing eastward, you subtract one. The line roughly follows the 180° meridian but zigzags to keep island groups like Kiribati on one date. The Diomede islands in the strait are just 4 km apart, but a day apart.
Answer as per the official UPSC answer key.
With reference to “water vapour”, which of the following statements is/are correct ?
- 1. It is a gas, the amount of which decreases with altitude.
- 2. Its percentage is maximum at the poles.
Select the answer using the code given below :
Answer (a) & explanation
Only statement 1 is correct (a). Statement 1 is right: water vapour is a variable gas, and most of it lies in the lowest few kilometres of the air. It decreases with altitude, because colder air holds less moisture. Statement 2 is wrong: water vapour makes up as much as about 4% of the air in the warm, wet tropics, but less than 1% in cold, dry polar air. So it is lowest at the poles, not highest.
Notice why it matters: water vapour is the most important natural greenhouse gas, and it gives us clouds and rain. It also releases latent heat when it condenses, which powers thunderstorms and cyclones. A warmer world holds more water vapour, about 7% more per degree Celsius, which makes extreme rain heavier.
Answer as per the official UPSC answer key.
Consider the following description :
- 1. Annual and daily range of temperatures is low.
- 2. Precipitation occurs throughout the year.
- 3. Precipitation varies between 50 cm – 250 cm.
What is this type of climate ?
Answer (d) & explanation
This is the Marine West Coast climate (d). The Marine West Coast, or British type, climate lies on the western sides of continents between about 45° and 60° latitude. Onshore westerlies and warm currents moderate it, so both annual and daily temperature ranges are low. Cyclones bring rain in every month, and the total is moderate, about 50–250 cm. Option (a) is wrong: equatorial climates get much more rain, usually over 200 cm, from daily convection. Options (b) and (c), the China type and humid subtropical, have hot summers and a wider temperature range.
Notice where it is found: north-west Europe, British Columbia, southern Chile and New Zealand. Its typical forests are deciduous trees like oak and beech, and it suits dairy farming.
The equatorial climate also has a low temperature range and year-round rain. The 50–250 cm figure is what rules it out.
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Answer as per the official UPSC answer key.
With reference to “Coriolis force”, which of the following statements is/are correct ?
- 1. It increases with increase in wind velocity.
- 2. It is maximum at the poles and is absent at the equator.
Select the answer using the code given below :
Answer (c) & explanation
Both statements are correct (c). The Coriolis force comes from the Earth's rotation; its formula is 2Ωv sin φ, where v is wind speed and φ is latitude. Statement 1 is right: it increases with wind speed. Statement 2 is right: it depends on the sine of latitude, so it is zero at the equator and greatest at the poles. It deflects winds to the right in the northern hemisphere and to the left in the southern hemisphere.
Notice the result: cyclones cannot form within about 5° of the equator, because there is too little Coriolis force to make the air spin. This deflection also creates the trade winds, the westerlies and the circular flow of ocean currents, called gyres.
Answer as per the official UPSC answer key.
On June 21 every year, which of the following latitude(s) experience(s) a sunlight of more than 12 hours ?
- 1. Equator
- 2. Tropic of Cancer
- 3. Tropic of Capricorn
- 4. Arctic Circle
Select the correct answer using the code given below :
Answer (d) & explanation
The Tropic of Cancer and the Arctic Circle get more than 12 hours (d). On 21 June, the June solstice, the northern hemisphere is tilted towards the Sun, so days are longer than 12 hours everywhere north of the equator. Item 2 is right: the Tropic of Cancer gets about 13½ hours, and the Sun is overhead there at noon. Item 4 is right: the Arctic Circle gets 24 hours of daylight. Item 1 is wrong: the equator always has about 12 hours. Item 3 is wrong: the Tropic of Capricorn has its shortest day, about 10½ hours.
Notice the midnight Sun in places like northern Norway and Alaska. India's longest day falls on 21 June, and the Tropic of Cancer passes through eight Indian States.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement-I : The atmosphere is heated more by incoming solar radiation than by terrestrial radiation.
Statement-II : Carbon dioxide and other greenhouse gases in the atmosphere are good absorbers of long wave radiation.
Which one of the following is correct in respect of the above statements ?
Answer (d) & explanation
Statement I is wrong but Statement II is correct (d). Statement II is right: carbon dioxide, water vapour and other greenhouse gases are good absorbers of long-wave radiation. Statement I is wrong: incoming short-wave sunlight mostly passes through the air without heating it much. The Earth's surface absorbs it, warms up, and gives off long-wave terrestrial radiation, which the greenhouse gases absorb. So the atmosphere is heated mainly from below, by terrestrial radiation, not directly by the Sun.
Notice why temperature falls with height in the troposphere, about 6.5°C per km, the normal lapse rate: the air is warmest near its heat source, the ground. This is also the basis of the greenhouse effect, which keeps the Earth about 33°C warmer than it would otherwise be.
The air is warmest near the ground and cools with height. That pattern itself shows heating from below.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement-I : Thickness of the troposphere at the equator is much greater as compared to poles.
Statement-II : At the equator, heat is transported to great heights by strong convectional currents.
Which one of the following is correct in respect of the above statements ?
Answer (a) & explanation
Both statements are correct and II explains I (a). Statement I is right: the troposphere is about 18 km thick at the equator and only about 8 km at the poles. Statement II is right and is the reason: over the hot equator, strong convection currents carry heat and air to great heights, pushing the top of the layer, the tropopause, much higher. At the cold poles, the air sinks and stays low. The troposphere is also slightly thicker in summer than in winter for the same reason.
Notice that almost all weather, clouds and rain happen in the troposphere, which holds about 75–80% of the atmosphere's mass. Above it, the stratosphere holds the ozone layer and is calm, so jet aircraft cruise near its base.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Pyroclastic debris
- 2. Ash and dust
- 3. Nitrogen compounds
- 4. Sulphur compounds
How many of the above are products of volcanic eruptions ?
Answer (d) & explanation
All four are products of volcanic eruptions (d). Item 1 is right: an eruption throws out pyroclastic debris: bombs, lapilli and cinders. Item 2 is right: it sends up clouds of fine ash and dust, which can ground flights, as Iceland's Eyjafjallajökull did in 2010. Items 3 and 4 are right: the gases are mainly water vapour and carbon dioxide, with sulphur compounds such as sulphur dioxide and hydrogen sulphide, and nitrogen compounds.
Notice the climate effect: sulphur dioxide forms tiny sulphate aerosols in the stratosphere that reflect sunlight and cool the Earth. Mount Pinatubo (1991) cooled the globe by about 0.5°C for a year or two. India's only active volcano is on Barren Island in the Andamans.
Answer as per the official UPSC answer key.
Which of the following is/are correct inference/inferences from isothermal maps in the month of January ?
- 1. The isotherms deviate to the north over the ocean and to the south over the continent.
- 2. The presence of cold ocean currents, Gulf Stream and North Atlantic Drift make the North Atlantic Ocean colder and the isotherms bend towards the north.
Select the answer using the code given below :
Answer (a) & explanation
Only statement 1 is correct (a). Statement 1 is right: in January, the northern winter, the oceans stay warmer than the land. So isotherms, lines joining places of equal temperature, bend north (poleward) over the oceans and south (equatorward) over the cold continents. Statement 2 is wrong: the Gulf Stream and North Atlantic Drift are warm currents, not cold ones. They make the North Atlantic warmer, which is why the isotherms bend far north there.
Notice the result: the warm drift keeps ports of Norway and north-west Europe ice-free in winter, while places at the same latitude in Canada freeze. In July, the pattern reverses: isotherms bend poleward over the hot land and equatorward over the cooler sea.
Statement 2 has the right result (isotherms bend north) for the wrong reason (it calls the currents cold).
Answer as per the official UPSC answer key.
Consider the following statements :
Statement-I : Rainfall is one of the reasons for weathering of rocks.
Statement-II : Rain water contains carbon dioxide in solution.
Statement-III : Rain water contains atmospheric oxygen.
Which one of the following is correct in respect of the above statements ?
Answer (a) & explanation
Both II and III are correct and both explain I (a). Statement I is right: rain is a major cause of chemical weathering. Statement II is right and explains it: rainwater dissolves carbon dioxide from the air and becomes weak carbonic acid, which dissolves limestone; this is carbonation, which forms caves and karst landscapes. Statement III is right and also explains it: dissolved oxygen reacts with iron-bearing minerals, turning them rusty red and weak; this is oxidation. Each explains Statement I on its own.
Notice the other kinds: hydration (minerals absorb water and swell) and solution. Mechanical weathering, such as frost wedging and the exfoliation of rocks in deserts, breaks rocks without changing them chemically. Hot, wet climates have the fastest chemical weathering.
Answer as per the official UPSC answer key.
With reference to the Earth’s atmosphere, which one of the following statements is correct?
Answer (c) & explanation
Infrared is largely absorbed by water vapour in the lower atmosphere (c). Option (c) is right: water vapour, which is concentrated near the surface, and carbon dioxide absorb most of the infrared heat, which is why they are greenhouse gases. Option (a) is wrong: the equator gets only about 2.5 times the yearly insolation of the poles, not 10 times. Option (b) is wrong: infrared is roughly half of incoming sunlight, not two-thirds; visible light is a large share too. Option (d) is wrong: infrared lies outside the visible band, beyond red.
Notice why the air is heated from below: sunlight passes through, warms the ground, and the ground gives off infrared that the lower air absorbs. That is why temperature falls with height in the troposphere.
Answer as per the official UPSC answer key.
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?
Answer (d) & explanation
Statement I is wrong but Statement II is correct (d). Statement II is right: water has a much higher specific heat than rock and soil, so the oceans warm and cool slowly, while land heats and cools fast. Statement I is marked wrong: UPSC's key treats the land–sea temperature contrast as greater in winter, when continental interiors such as Siberia become extremely cold while the oceans stay mild. So the difference in winter is larger than in summer.
Notice the effects: continental climates have a big range between summer and winter, while maritime climates stay mild. The land–sea contrast also drives land and sea breezes daily and the monsoon seasonally. The Siberian High in winter is the result of this deep cold.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. In a seismograph, P waves are recorded earlier than S waves.
- 2. In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.
Which of the statements given above is/are correct?
Answer (c) & explanation
Both statements are correct (c). Statement 1 is right: P (primary) waves are the fastest seismic waves, so a seismograph records them first, before S (secondary) waves. Statement 2 is right: P waves are longitudinal: particles vibrate back and forth along the direction of travel, like sound. S waves are transverse: particles move up and down, at right angles to the direction of travel.
Notice what they reveal about the Earth. P waves pass through solids, liquids and gases, but S waves cannot pass through liquids. Since S waves do not cross the outer core, creating a shadow zone, we know the outer core is liquid. Surface waves come last and cause the most damage. The gap between P and S arrival tells the distance to the epicentre.
Answer as per the official UPSC answer key.
In the northern hemisphere, the longest day of the year normally occurs in the :
Answer (b) & explanation
The longest day is in the second half of June (b). The summer solstice falls on 20–21 June, when the sun is overhead at the Tropic of Cancer (23.5° N). That gives the northern hemisphere its longest day and shortest night. North of the Arctic Circle, the sun does not set at all. So option (b), the second half of June, is right. Options (a), (c) and (d) miss the solstice date.
Notice the other key dates: the winter solstice (shortest day) on 21–22 December, when the sun is over the Tropic of Capricorn, and the equinoxes on about 21 March and 23 September, when day and night are nearly equal. The seasons happen because Earth's axis is tilted by about 23.5°.
Answer as per the official UPSC answer key.