UPSC CSE Prelims
World Geography Previous Year Questions (PYQs)

Detailed Explanation:

Scientific studies confirm that the Earth's rotational axis is gradually shifting, a phenomenon known as polar drift. Melting polar ice redistributes mass from the poles toward the equator, changing the Earth's moment of inertia and affecting its rotation. Solar flares and CMEs do impact the upper atmosphere, but they do not significantly alter the Earth's rotational axis.

✅ Statement I is Correct: Satellite observations show that Earth's rotational axis is drifting and its rotation rate is changing slightly.

✅ Statement II is Correct: Solar flares and CMEs transfer large amounts of energy to the thermosphere and magnetosphere.

✅ Statement III is Correct: Melted polar ice redistributes water toward lower latitudes, especially near the equator.

❌ Statement II does NOT explain Statement I: Solar activity affects the atmosphere and satellites but not the Earth's rotational axis significantly.

✅ Statement III explains Statement I: Redistribution of mass from poles to equator changes Earth's moment of inertia, causing polar drift and slight rotational changes.

Concept Note:

Moment of Inertia is the resistance of a rotating object to changes in its rotation. When mass moves away from the rotational axis (toward the equator), the moment of inertia increases, leading to changes in rotational speed and axis orientation.

Detailed Explanation:

Answer: Option 4 — Statement-I is incorrect, but Statement-II is correct

This question tests understanding of atmospheric heating mechanisms and the greenhouse effect. Statement-I incorrectly suggests that incoming solar radiation heats the atmosphere more than terrestrial radiation, while Statement-II correctly describes the greenhouse gas absorption properties.

❌ Statement-I – Incorrect: The atmosphere is heated more by terrestrial (long wave) radiation than by incoming solar (short wave) radiation. Solar radiation mostly passes through the atmosphere without being absorbed, whereas the Earth's surface absorbs solar energy and re-radiates it as long wave radiation, which is then absorbed by greenhouse gases in the atmosphere, heating it.

✅ Statement-II – Correct: Carbon dioxide and other greenhouse gases are indeed good absorbers of long wave (infrared) radiation emitted by the Earth's surface, which is the fundamental principle of the greenhouse effect.

📝 Short Notes: Atmospheric Heating and Earth's Heat Budget

• Insolation: Incoming solar radiation reaches Earth in short waves (0.2 to 4 micrometers). Most of it passes through the atmosphere with minimal absorption.
• Terrestrial Radiation: Earth's surface absorbs solar energy and re-radiates it as long wave infrared radiation (4 to 80 micrometers).
• Atmospheric Heating: The atmosphere is largely transparent to incoming short wave solar radiation but opaque to outgoing long wave terrestrial radiation due to greenhouse gases.
• Greenhouse Effect: CO₂, water vapor, methane, and other greenhouse gases absorb long wave radiation, warming the lower atmosphere. This is why the atmosphere is heated more from below (by terrestrial radiation) than from above (by solar radiation).
• Heat Budget Components: Of the solar radiation reaching Earth, approximately 35% is reflected back, 14% is absorbed by the atmosphere, and 51% is absorbed by the Earth's surface. The surface then heats the atmosphere through radiation, conduction, and convection.
• Albedo Effect: About 30% of incoming solar radiation is reflected by clouds, atmospheric particles, and the Earth's surface without heating the atmosphere significantly.

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

The Coriolis force is an apparent deflection force caused by Earth's rotation, affecting moving objects including wind and ocean currents. Both statements about the Coriolis force are correct based on fundamental principles of atmospheric and oceanographic dynamics.

✅ Statement 1 – Correct: The Coriolis force is directly proportional to the velocity of the moving object (F = 2mΩv sinφ), so higher wind velocity results in greater Coriolis force and deflection.

✅ Statement 2 – Correct: The Coriolis force varies with the sine of latitude (sinφ), being maximum at the poles (sin 90° = 1) and zero at the equator (sin 0° = 0), where no deflection occurs.

📝 Short Notes: Coriolis Force

• Definition: An apparent deflection force acting on moving objects due to Earth's rotation, named after French scientist Gaspard-Gustave de Coriolis.
• Mathematical Expression: F = 2mΩv sinφ, where m = mass, Ω = Earth's angular velocity, v = object velocity, φ = latitude.
• Direction of Deflection: Objects are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• Latitudinal Variation: Zero at the equator, increases with latitude, and maximum at the poles; this explains why tropical cyclones do not form within 5° of the equator.
• Dependency on Velocity: Greater the speed of the moving object (wind, ocean current, missile), greater the Coriolis deflection.
• Impact on Wind Patterns: Responsible for the rotation of cyclones, anticyclones, trade winds deflection, and the geostrophic wind balance.
• Ocean Currents: Causes major ocean currents to flow in circular patterns (gyres) - clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere.
• Practical Applications: Critical for long-range artillery, missile trajectories, aviation routes, and understanding global circulation patterns.

Detailed Explanation:

Answer: Option 4 — 2 and 4

On June 21, the Summer Solstice in the Northern Hemisphere, the sun's rays are directly overhead at the Tropic of Cancer, and all latitudes north of the Equator experience daylight longer than 12 hours. The Arctic Circle experiences 24 hours of continuous daylight (Midnight Sun), while the Equator always has exactly 12 hours of daylight throughout the year.

✅ Statement 1 (Equator) – Incorrect: The Equator experiences exactly 12 hours of daylight on all days of the year, not more than 12 hours.
✅ Statement 2 (Tropic of Cancer) – Correct: On June 21, the Tropic of Cancer receives direct sunlight and experiences more than 12 hours of daylight.
❌ Statement 3 (Tropic of Capricorn) – Incorrect: The Tropic of Capricorn lies in the Southern Hemisphere, which is tilted away from the Sun on June 21, resulting in less than 12 hours of daylight.
✅ Statement 4 (Arctic Circle) – Correct: The Arctic Circle experiences 24 hours of continuous daylight on June 21, known as the Midnight Sun phenomenon.

📝 Short Notes: Summer Solstice and Day Length

• Summer Solstice (June 21): The Northern Hemisphere is tilted at its maximum (23.5°) toward the Sun, resulting in the longest day of the year in the Northern Hemisphere.
• Direct Rays at Tropic of Cancer: On this day, the sun's rays fall vertically at the Tropic of Cancer (23.5° N), which receives maximum solar energy.
• Day Length Pattern: All latitudes north of the Equator experience more than 12 hours of daylight on June 21, with day length increasing toward the North Pole.
• Equator: The Equator experiences exactly 12 hours of daylight and 12 hours of night on all days of the year due to its position midway between the poles.
• Midnight Sun: At the Arctic Circle (66.5° N) and all latitudes beyond it toward the North Pole, the sun does not set on June 21, resulting in 24 hours of continuous daylight.
• Southern Hemisphere: On June 21 (Winter Solstice in Southern Hemisphere), all latitudes south of the Equator experience less than 12 hours of daylight, with the Antarctic Circle experiencing 24 hours of darkness.
• Tropic of Capricorn: Located at 23.5° S, it experiences its shortest day on June 21 with significantly less than 12 hours of daylight.

Detailed Explanation:

Answer: Option 4 — Marine West coast climate

The Marine West Coast climate (Cfb in Köppen classification) is characterized by low annual and daily temperature ranges due to oceanic moderation, year-round precipitation brought by prevailing westerly winds, and precipitation totals typically ranging from 50-250 cm. This climate is found on western coasts of continents between 40°-60° latitude, such as the Pacific Northwest of North America and Western Europe.

📝 Short Notes: Marine West Coast Climate

• Location: Found on western coasts of continents between 40°-60° latitude (e.g., Pacific Northwest USA, British Columbia, Western Europe, Southern Chile, Southeast Australia, New Zealand)
• Temperature Characteristics: Mild winters (above 0°C) and cool summers (below 22°C); narrow annual temperature range due to maritime influence; typically no month averages below -3°C
• Precipitation Pattern: Year-round rainfall with slight winter maximum; brought by mid-latitude cyclones and orographic lifting; ranges from 50-250 cm annually depending on topography
• Atmospheric Controls: Dominated by prevailing westerlies that carry moist oceanic air; frequent passage of frontal systems and cyclonic storms; maritime air masses moderate temperature extremes
• Vegetation: Dense evergreen and deciduous forests; includes temperate rainforests in areas with higher precipitation; characteristic species include Douglas fir, redwood, spruce, and beech
• Distinguishing Features: Cloudy, foggy conditions common; low sunshine hours; high relative humidity; minimal temperature extremes compared to continental interiors at similar latitudes
• Contrast with Other Climates: Unlike Mediterranean climate (dry summers), Marine West Coast has year-round precipitation; unlike Humid Subtropical (hot summers), it has cool summers; unlike Equatorial (high temperatures year-round), it has distinct seasonal temperature variation though mild

Detailed Explanation:

Answer: Option 1 — 1 only

Statement 1 is correct because water vapour concentration decreases with altitude as colder air at higher elevations has a reduced capacity to hold moisture. Statement 2 is incorrect because water vapour percentage is maximum near the equator (due to higher temperatures and evaporation) and minimum at the poles, not the other way around.

✅ Statement 1 – Correct: Water vapour is a gas that decreases with altitude because temperature drops at higher elevations, reducing the air's moisture-holding capacity.
❌ Statement 2 – Incorrect: Water vapour percentage is maximum at the equator (warm, high evaporation) and minimum at the poles (cold, low evaporation).

📝 Short Notes: Atmospheric Water Vapour

• Nature: Water vapour is an invisible gas and the most variable component of the atmosphere, ranging from 0% to 4% by volume.
• Vertical Distribution: Concentration decreases rapidly with altitude; about 50% of atmospheric water vapour is found below 2 km, and 90% below 6 km altitude.
• Horizontal Distribution: Maximum concentration occurs in the equatorial region (hot, high evaporation) and decreases towards the poles (cold, low evaporation).
• Temperature Dependency: Warm air can hold more moisture than cold air; at 30°C, air can hold about 4 times more water vapour than at 0°C.
• Role in Weather: Water vapour is crucial for cloud formation, precipitation, and latent heat transfer, which drives weather systems and storms.
• Greenhouse Gas: Water vapour is the most abundant greenhouse gas, contributing significantly to the natural greenhouse effect and Earth's temperature regulation.
• Sources: Primarily from evaporation of ocean water (oceans cover 71% of Earth's surface), followed by lakes, rivers, soil moisture, and transpiration from plants.

Detailed Explanation:

Answer: Option 2 — Only two

This question tests the correct matching of mountain ranges with their regions and types. Out of the four given rows, only two contain completely accurate information regarding the region, name, and type of mountain range.

❌ Row 1 – Incorrect: The Vosges are located in Europe (eastern France), not Central Asia, and they are block mountains, not fold mountains.

❌ Row 2 – Incorrect: The Alps are correctly placed in Europe, but they are fold mountains formed by the collision of the African and Eurasian plates, not block mountains.

✅ Row 3 – Correct: The Appalachian Mountains are located in North America and are old fold mountains formed during the Paleozoic era.

✅ Row 4 – Correct: The Andes are located in South America and are young fold mountains formed by the subduction of the Nazca Plate beneath the South American Plate.

📝 Short Notes: Mountain Types and Formation

• Young Fold Mountains: Himalayas, Alps, Andes, Rockies — formed during the Tertiary period (66-2.6 million years ago); characterized by high peaks, sharp ridges, and active tectonic activity.
• Old Fold Mountains: Appalachians, Urals, Aravallis — formed during Paleozoic or earlier eras; extensively eroded with rounded peaks and lower elevations.
• Vosges and Black Forest: Classic examples of block mountains in Europe, formed by the same faulting process that created the Rhine Rift Valley between them.
• Plate Tectonics and Mountains: Most major mountain ranges are associated with convergent plate boundaries (fold mountains) or divergent boundaries with rifting (block mountains).

Detailed Explanation:

Answer: Option 3 — Côte d'Ivoire and Ghana

Côte d'Ivoire (Ivory Coast) and Ghana are the two largest cocoa producers in the world, together accounting for more than 60% of global cocoa production. West Africa dominates cocoa production, with these two countries leading the industry due to favorable climatic conditions and extensive cultivation.

📝 Short Notes: Global Cocoa Production

• West Africa's Dominance: West Africa produces approximately 70% of the world's cocoa, with Côte d'Ivoire and Ghana being the top two producers globally.
• Côte d'Ivoire: The world's largest cocoa producer, accounting for about 40-45% of global production, with approximately one million cocoa farmers supplying major companies like Nestlé, Mars, and Hershey.
• Ghana: The second-largest producer, contributing about 20% of global cocoa production, known for high-quality cocoa beans.
• Other Producers: Indonesia, Ecuador, Cameroon, and Nigeria are other significant cocoa-producing countries, but their combined output is much less than West Africa.
• Climatic Requirements: Cocoa thrives in tropical climates with high temperatures (21-32°C), high humidity, and well-distributed rainfall, typically within 10-20 degrees of the equator.
• Environmental Impact: Large-scale cocoa cultivation has led to significant deforestation in West Africa, particularly in Côte d'Ivoire, where forests have been cleared for cocoa plantations.
• Economic Significance: Cocoa is a major export commodity for West African countries, providing livelihoods for millions of smallholder farmers but also facing challenges like price volatility and labor issues.

Detailed Explanation:

Answer: Option 1 — Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

The troposphere is indeed thicker at the equator (approximately 16-18 km) compared to the poles (approximately 8-10 km) due to differential heating and thermal expansion. The intense solar radiation at the equator generates strong convectional currents that transport heat vertically to great heights, causing the air to expand and thereby increasing the thickness of the troposphere. Statement-II provides a direct causal explanation for the phenomenon described in Statement-I.

✅ Statement-I – Correct: The troposphere's thickness at the equator (16-18 km) is significantly greater than at the poles (8-10 km) due to greater heating and air expansion.
✅ Statement-II – Correct: Strong convectional currents at the equator, driven by intense solar heating, transport heat vertically to great heights, directly causing the increased tropospheric thickness.

📝 Short Notes: Troposphere and Atmospheric Structure

• Troposphere Characteristics: The lowest layer of the atmosphere where all weather phenomena occur, containing approximately 75% of the atmosphere's mass and almost all water vapor.
• Thickness Variation: Troposphere thickness varies from 8-10 km at the poles to 16-18 km at the equator, averaging about 13 km globally.
• Equatorial Heating: The equator receives more direct and intense solar radiation throughout the year, causing maximum surface heating and air temperature.
• Convectional Currents: Hot air at the equator rises rapidly due to lower density, creating strong vertical currents that transport heat to higher altitudes (part of the Hadley Cell circulation).
• Thermal Expansion: Warmer air occupies greater volume, causing the atmospheric column to expand vertically at the equator, increasing tropospheric height.
• Temperature Lapse Rate: Temperature decreases with altitude in the troposphere at an average rate of 6.5°C per kilometer until reaching the tropopause.
• Tropopause Variation: The tropopause (boundary between troposphere and stratosphere) is higher and colder at the equator (-80°C) than at the poles (-45°C).

Detailed Explanation:

Answer: Option 1 — Both Statement-II and Statement-III are correct and both of them explain Statement-I

Rainfall is a significant agent of weathering, particularly chemical weathering. Rainwater absorbs carbon dioxide from the atmosphere forming weak carbonic acid, and also dissolves atmospheric oxygen. Both these dissolved gases actively participate in breaking down rock minerals through chemical reactions.

✅ Statement I – Correct: Rainfall causes both physical and chemical weathering of rocks through impact and chemical reactions.
✅ Statement II – Correct: Rainwater dissolves atmospheric CO₂, forming carbonic acid (H₂CO₃) which chemically weathers rocks.
✅ Statement III – Correct: Rainwater contains dissolved atmospheric oxygen which causes oxidation of minerals, a form of chemical weathering.

📝 Short Notes: Chemical Weathering by Rainwater

• Carbonation: CO₂ in rainwater forms carbonic acid (H₂CO₃), which reacts with carbonate rocks (limestone, marble) and feldspars, dissolving them over time.
• Oxidation: Dissolved oxygen in rainwater reacts with iron-bearing minerals (like olivine, pyroxene) causing rust-like decomposition, weakening rock structure.
• Hydrolysis: Water molecules react with silicate minerals (feldspars, micas) to form clay minerals, contributing to rock breakdown.
• Solution: Rainwater can directly dissolve soluble minerals like halite and gypsum without additional chemical reactions.
• pH Factor: Natural rainwater has a pH of approximately 5.6 due to dissolved CO₂; acid rain (pH < 5.0) accelerates weathering rates significantly.
• Rate Factors: Weathering rate depends on rainfall intensity, temperature, rock composition, and vegetation cover which can either enhance or reduce weathering.
• Physical Impact: Besides chemical action, heavy rainfall causes mechanical weathering through raindrop impact and frost wedging in cold climates.

Detailed Explanation:

Answer: Option 2 — Only two

Among the four countries listed, only Germany and Norway have a border with the North Sea. Finland borders the Baltic Sea and the Gulf of Bothnia, while Russia's European coastline touches the Baltic Sea, Black Sea, and Arctic Ocean, but not the North Sea.

✅ Germany – Correct: Germany has a northern coastline along the North Sea, with major ports like Hamburg and Bremerhaven.
✅ Norway – Correct: Norway has an extensive coastline along the North Sea on its southwestern side.
❌ Finland – Incorrect: Finland is located on the Baltic Sea and does not have access to the North Sea.
❌ Russia – Incorrect: Russia does not border the North Sea; its nearest sea in the region is the Baltic Sea.

📝 Short Notes: North Sea Geography

• Location: The North Sea is a marginal sea of the Atlantic Ocean located between Great Britain, Scandinavia, Germany, the Netherlands, Belgium, and France.
• Bordering Countries: Seven countries border the North Sea – United Kingdom, Norway, Denmark, Germany, the Netherlands, Belgium, and France.
• Important Ports: Major ports include Rotterdam (Netherlands), Hamburg (Germany), Antwerp (Belgium), and Aberdeen (UK).
• Economic Significance: The North Sea is rich in petroleum and natural gas reserves, making it one of the world's most important oil-producing regions.
• Fisheries: Historically one of the world's most productive fishing grounds, though overfishing has depleted stocks in recent decades.
• Strategic Importance: The North Sea has been strategically important for trade routes and naval operations throughout European history.
• Connection to Baltic Sea: The North Sea connects to the Baltic Sea through the Skagerrak and Kattegat straits between Denmark, Norway, and Sweden.

Detailed Explanation:

Answer: Option 4 — All four

All four items listed—pyroclastic debris, ash and dust, nitrogen compounds, and sulphur compounds—are products of volcanic eruptions. Volcanic eruptions release both solid materials (pyroclastic debris, ash) and various gases (nitrogen and sulphur compounds) that can have significant environmental impacts.

✅ Statement 1 – Correct: Pyroclastic debris includes fragmental materials like ash, pumice, cinders, and volcanic bombs ejected during eruptions.
✅ Statement 2 – Correct: Ash and dust are fine-grained particles of volcanic rock and glass produced during explosive volcanic activity.
✅ Statement 3 – Correct: Nitrogen compounds such as ammonia (NH₃) and nitrogen oxides (NOₓ) are released from volcanic gases.
✅ Statement 4 – Correct: Sulphur compounds, particularly sulphur dioxide (SO₂) and hydrogen sulphide (H₂S), are major volcanic gases.

📝 Short Notes: Products of Volcanic Eruptions

• Environmental Impact: Volcanic ash can disrupt air travel, damage crops, and contaminate water supplies; sulphur dioxide contributes to acid rain and can affect global climate by forming aerosols in the stratosphere.
• Tephra: General term for all pyroclastic material ejected during an eruption, regardless of size or composition.
• Volcanic Winter: Large eruptions releasing significant ash and SO₂ can block sunlight, temporarily cooling the Earth's surface.
• Health Hazards: Fine volcanic ash can cause respiratory problems; gases like SO₂ and H₂S are toxic in high concentrations.

Detailed Explanation:

Answer: Option 1 — 1 only

In January (Northern Hemisphere winter), continents cool down faster than oceans due to differential heating. This causes isotherms to deviate northward over the warmer oceans and southward over the colder continents. Statement 2 is incorrect because the Gulf Stream and North Atlantic Drift are warm ocean currents, not cold, and they actually make the North Atlantic warmer, causing isotherms to bend northward.

✅ Statement 1 (Isotherm Deviation) – Correct: In January, isotherms deviate northward over oceans (which remain warmer) and southward over continents (which are colder) in the Northern Hemisphere due to differential heating and cooling rates of land and water.

❌ Statement 2 (Gulf Stream and North Atlantic Drift) – Incorrect: The Gulf Stream and North Atlantic Drift are warm ocean currents, not cold; they carry warm tropical water northward, making the North Atlantic relatively warmer and causing isotherms to bend northward, not making it colder.

📝 Short Notes: Isotherms and Ocean Currents

• Isotherms: Lines on a map connecting points of equal temperature, used to understand temperature distribution patterns across different regions and seasons.
• January Isotherm Pattern (Northern Hemisphere): During winter, continents are colder than oceans because land loses heat faster than water. Isotherms bend equatorward (southward) over continents and poleward (northward) over oceans.
• July Isotherm Pattern (Northern Hemisphere): During summer, continents are warmer than oceans. Isotherms bend poleward (northward) over continents and equatorward (southward) over oceans.
• Gulf Stream: A powerful warm ocean current originating in the Gulf of Mexico, flowing along the eastern coast of North America and across the Atlantic towards Europe, significantly warming Western Europe's climate.
• North Atlantic Drift: The extension of the Gulf Stream that continues eastward across the North Atlantic, bringing warm water and mild temperatures to Northwestern Europe, including the British Isles and Scandinavia.
• Effect of Ocean Currents on Isotherms: Warm currents like the Gulf Stream cause isotherms to bend poleward (northward in Northern Hemisphere), while cold currents like the Labrador Current cause isotherms to bend equatorward (southward in Northern Hemisphere).
• Differential Heating: Water has a higher specific heat capacity than land, meaning oceans heat up and cool down more slowly than continents, creating seasonal temperature contrasts that influence isotherm patterns.

Detailed Explanation:

Answer: Option 1 — 1, 2 and 4

Italy, Japan, and South Korea are frequently mentioned in global media for their extremely low fertility rates, rapidly ageing populations, and projected population declines. These countries face significant demographic challenges including shrinking workforces, increased healthcare costs, and pension sustainability issues.

Nigeria has a very young and rapidly growing population, while South Africa's population growth has slowed but is not yet declining. Neither country is characterized by low birth rates or ageing population concerns that dominate discussions about Italy, Japan, and South Korea.

📝 Short Notes: Global Demographic Trends and Population Ageing

• Demographic Dividend vs Demographic Burden: Countries with young populations (Nigeria) potentially benefit from demographic dividend, while ageing societies face economic burdens from increased dependency ratios.
• Economic Implications: Low birth rates lead to shrinking workforces, reduced consumption, decreased tax revenues, and challenges in sustaining pension and healthcare systems.
• Policy Responses: Japan, Italy, and South Korea have implemented various measures including childcare support, parental leave policies, immigration reforms, and automation to address demographic challenges.

Detailed Explanation:

Answer: Option 1 — Canada and the United States of America

The border between Canada and the United States is the longest international border in the world, stretching approximately 8,891 kilometers (5,525 miles), including the border shared with Alaska. It is a peaceful, mostly undefended boundary that includes both land and water segments, exemplifying one of the most stable and cooperative international relationships in modern history.

📝 Short Notes: Longest International Borders in the World

• Canada-US Border Characteristics: The border runs through diverse terrain including forests, mountains, lakes, and rivers; it includes the Great Lakes and crosses through remote wilderness areas.
• Peace and Cooperation: The Canada-US border is often cited as the world's longest undefended border, symbolizing peaceful coexistence and strong bilateral relations.
• Historical Context: Established through various treaties including the Treaty of Paris (1783) and the Oregon Treaty (1846).