Which one among the following is not an important factor of climate of an area ?

1. Weather vs. Climate: The Fundamentals (basic)

Welcome to your first step in mastering world climates! To understand how the world is divided into different climatic zones, we must first distinguish between two terms we often use interchangeably: Weather and Climate. While they share the same DNA, they operate on completely different timescales.

Weather is the momentary state of the atmosphere at any given place and time. It is what you see when you look out your window right now—is it raining, sunny, or windy? Because the atmosphere is dynamic, weather can fluctuate wildly within a single day. You might start your morning with a clear sky and end it with a heavy downpour. As noted in Exploring Society: India and Beyond, Class VII, p.46, weather refers to what we experience every hour or day.

Climate, on the other hand, represents the average of these weather conditions over a much longer duration—typically a period of 30 years or more. If weather is the "mood" of the atmosphere, climate is its "personality." For instance, while a desert might have a rainy day (weather), its long-term state remains arid (climate). This distinction is vital for UPSC, as climate determines a region’s vegetation, agriculture, and lifestyle CONTEMPORARY INDIA-I, Class IX, p.26.

Interestingly, the building blocks for both are identical. These are known as the elements of weather and climate:

• Temperature: The degree of hotness or coldness.
• Atmospheric Pressure: The weight of the air above us.
• Wind: The movement of air from high to low pressure.
• Humidity and Precipitation: The moisture content and its fall as rain, snow, or hail Certificate Physical and Human Geography, GC Leong, p.115.

Feature	Weather	Climate
Duration	Short-term (minutes to days).	Long-term (30+ years average).
Area	Specific, small area.	Large geographical region.
Changeability	Changes very frequently.	Remains stable over decades.

Sources: Exploring Society: India and Beyond, Class VII, Understanding the Weather / Climates of India, p.42, 46; CONTEMPORARY INDIA-I, Class IX, Climate, p.26; INDIA PHYSICAL ENVIRONMENT, Class XI, Climate, p.28; Certificate Physical and Human Geography, GC Leong, Weather, p.115

2. Solar Radiation and the Role of Latitude (basic)

At the heart of global climate lies Insolation, which is short for Incoming Solar Radiation. The most fundamental reason why a jungle in Indonesia feels different from a tundra in Siberia is latitude. Because the Earth is a sphere, solar rays do not strike the surface uniformly. At the Equator, the sun's rays hit the Earth almost vertically (at a high angle), while toward the poles, they arrive at a sharp slant or a low angle of inclination. This variation is further influenced by the fact that the Earth's axis is tilted at an angle of 66½° with the plane of its orbit Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), Chapter 8: Solar Radiation, Heat Balance and Temperature, p.67.

The angle of the sun's rays dictates the intensity of heat in two major ways. First, Area of Spread: a vertical ray focuses all its energy on a small, concentrated area, whereas a slanted ray spreads the same amount of energy over a much larger surface, effectively diluting the heat. Second, Atmospheric Path: slanted rays must travel through a thicker layer of the atmosphere before reaching the surface. This results in more energy being lost to scattering, reflection, and absorption by clouds and water vapor Physical Geography by PMF IAS, Ocean temperature and salinity, p.511. Interestingly, while we think of the Equator as the hottest, the maximum insolation is actually received over subtropical deserts because they have the least cloud cover to block the sun, whereas the Equator often has cloudy skies that reflect some radiation back to space Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), Chapter 8: Solar Radiation, Heat Balance and Temperature, p.68.

Feature	Low Latitudes (Tropics)	High Latitudes (Poles)
Angle of Rays	Vertical / Direct	Slanted / Oblique
Energy Concentration	High (Small area)	Low (Large area)
Atmospheric Journey	Shorter distance	Longer distance (more loss)
Insolation Value	Approx. 320 Watt/m²	Approx. 70 Watt/m²

Sources: Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), Chapter 8: Solar Radiation, Heat Balance and Temperature, p.67; Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), Chapter 8: Solar Radiation, Heat Balance and Temperature, p.68; Physical Geography by PMF IAS, Ocean temperature and salinity, p.511

3. Altitude and the Normal Lapse Rate (intermediate)

When we discuss climate, we often focus on latitude, but Altitude (or elevation) is a powerful local modifier. Have you ever wondered why snow-capped peaks like Mount Kilimanjaro exist right on the Equator? This happens because the atmosphere is not heated from the top down by the sun, but rather from the bottom up by the Earth's surface through long-wave terrestrial radiation. As you move further away from this heat source (the ground), the temperature naturally drops. Fundamentals of Physical Geography, NCERT Class XI, Chapter 8, p. 70

This vertical decrease in temperature is known as the Lapse Rate. Under standard conditions, the temperature in the troposphere drops at a predictable pace called the Normal Lapse Rate, which is approximately 6.5°C for every 1,000 meters (or 1°C for every 165 meters) of ascent. This is why hill stations like Shimla or Ooty remain cool even when the surrounding plains are sweltering. Certificate Physical and Human Geography, GC Leong, Chapter 14, p. 131

To understand why this happens, we must look at air density and pressure. Gravity pulls most of the atmosphere's molecules close to the surface, making the air densest at sea level. As you climb higher, the atmospheric pressure decreases rapidly—on average by about 34 millibars for every 300 meters. Physical Geography by PMF IAS, Pressure Systems and Wind System, p. 305 Because thinner air at high altitudes has fewer molecules to absorb and retain heat, it cannot stay as warm as the dense air below. However, it's important to distinguish between the static environment and moving air:

Term	Description	Average Rate
Normal Lapse Rate (ELR)	The actual temperature change of the surrounding atmosphere at a fixed location.	~6.5°C / km
Dry Adiabatic Lapse Rate (DALR)	The rate at which a rising parcel of unsaturated air cools. Physical Geography by PMF IAS, Vertical Distribution of Temperature, p. 298	~9.8°C / km
Wet Adiabatic Lapse Rate (WALR)	The rate for a rising parcel of saturated air (slowed by latent heat release). Physical Geography by PMF IAS, Vertical Distribution of Temperature, p. 299	~4°C to 6°C / km

Sources: Fundamentals of Physical Geography, NCERT Class XI, Chapter 8: Solar Radiation, Heat Balance and Temperature, p.70; Certificate Physical and Human Geography, GC Leong, Chapter 14: Climate, p.131; Physical Geography by PMF IAS, Pressure Systems and Wind System, p.305; Physical Geography by PMF IAS, Vertical Distribution of Temperature, p.298-299

4. Atmospheric Pressure Belts and Planetary Winds (intermediate)

To understand global climate, we must first understand the planetary wind system, which acts as the Earth's primary heat distribution mechanism. Air moves from areas of high pressure to low pressure, but because the Earth rotates, these winds don't travel in a straight line. Instead, they are deflected by the Coriolis Force—to the right in the Northern Hemisphere and to the left in the Southern Hemisphere Certificate Physical and Human Geography, Chapter 14, p.139. This force is a function of latitude; it is absent at the equator and reaches its maximum strength at the poles FUNDAMENTALS OF PHYSICAL GEOGRAPHY NCERT 2025, Chapter 8, p.79. This is why you won't see large-scale cyclonic rotations crossing the equator! At the heart of this system lies the Equatorial Low-Pressure Belt (often called the Doldrums), located roughly between 10°N and 10°S. In this zone, intense solar heating causes air to expand and rise vertically through convection. Because the movement is primarily vertical, surface winds are often weak or absent, leading to the legendary 'calm' conditions reported by early sailors Physical Geography by PMF IAS, Pressure Systems and Wind System, p.311. As this moist air rises, it cools and condenses, forming massive cumulonimbus clouds that result in heavy daily convectional rainfall—a defining feature of tropical wet climates Physical Geography by PMF IAS, Pressure Systems and Wind System, p.312. Connecting these pressure belts are the Planetary Winds. The Trade Winds blow from the Sub-Tropical High-Pressure belts toward the Equatorial Low. Due to the Coriolis effect, they become the North-East Trades in the Northern Hemisphere and the South-East Trades in the Southern Hemisphere. The region where these two wind systems meet is known as the Intertropical Convergence Zone (ITCZ) Physical Geography by PMF IAS, Pressure Systems and Wind System, p.311. In the upper atmosphere, away from surface friction, the balance between the Pressure Gradient Force and the Coriolis Force creates Geostrophic Winds, which blow parallel to the isobars rather than across them Physical Geography by PMF IAS, Jet streams, p.384.

Sources: Certificate Physical and Human Geography, Chapter 14: Climate, p.139; FUNDAMENTALS OF PHYSICAL GEOGRAPHY NCERT 2025, Chapter 8: Atmospheric Circulation and Weather Systems, p.79; Physical Geography by PMF IAS, Pressure Systems and Wind System, p.311-312; Physical Geography by PMF IAS, Jet streams, p.384

5. Ocean Currents and Their Climatic Influence (intermediate)

To understand why a coastal city in Norway is milder in winter than a city in Canada at the same latitude, we must look at ocean currents. Think of ocean currents as massive, underwater conveyor belts that redistribute the sun’s energy across the globe. While latitude sets the baseline temperature, ocean currents act as a "climatic modifier," either boosting the heat or chilling the coast significantly. As noted in Certificate Physical and Human Geography, GC Leong, Chapter 14, p.134, these currents transport their internal temperature into adjacent landmasses, often overriding what we would expect based on latitude alone.

Warm currents originate in the tropics and flow toward the poles. Because warm air can hold more moisture, these currents usually bring heavy rainfall to coastal regions, especially when paired with onshore winds. For instance, the North Atlantic Drift (an extension of the Gulf Stream) keeps the ports of Western Europe ice-free even in the depths of winter, creating a "British Type" climate that is far warmer than it should be geographically Physical Geography, PMF IAS, Ocean Movements Ocean Currents and Tides, p.497. Conversely, cold currents flow from the poles toward the equator. They chill the air above them, leading to stable atmospheric conditions that suppress rain, often contributing to the formation of coastal deserts, though they also bring nutrient-rich waters to the surface through a process called upwelling Physical Geography, PMF IAS, Ocean Movements Ocean Currents and Tides, p.498.

The interaction between these currents and prevailing winds is the final piece of the puzzle. A current's temperature only affects the land if the wind blows onshore (from sea to land). If the wind blows offshore, the moderating effect is lost. This is why the eastern coasts of continents in temperate latitudes often experience different climatic extremes compared to western coasts, even if the currents offshore are similar Certificate Physical and Human Geography, GC Leong, Chapter 14, p.134.

Current Type	Origin	Impact on Temperature	Impact on Precipitation
Warm Current	Tropical/Equatorial	Raises temperature; keeps ports ice-free	Increases humidity and rainfall
Cold Current	Polar/High Latitude	Lowers summer temperatures; creates chill	Reduces rainfall; causes fog and aridity

Sources: Certificate Physical and Human Geography, GC Leong, Chapter 14: Climate, p.134; Physical Geography, PMF IAS, Ocean Movements Ocean Currents and Tides, p.497; Physical Geography, PMF IAS, Ocean Movements Ocean Currents and Tides, p.498

6. Continentality: Distance from the Sea (intermediate)

To understand Continentality, we must first look at a fundamental physical property: Differential Heating. Land surfaces heat up and cool down much faster than water bodies. This is because water has a higher specific heat capacity and involves vertical mixing, meaning it takes much more energy to raise the temperature of the ocean than the earth. As a result, the sea acts as a giant thermal reservoir that exerts a moderating influence on the climate of adjacent land masses Contemporary India-I, NCERT Class IX, Chapter 4, p.27.

As you move further inland, away from the coast, this moderating influence of the sea diminishes. Coastal regions experience equable or maritime climates, characterized by mild winters, cool summers, and a low annual range of temperature. In contrast, the interiors of large continents experience extreme weather conditions—scorching summers and freezing winters. This phenomenon is known as Continentality Contemporary India-I, NCERT Class IX, Chapter 4, p.27. For example, while a coastal city like Mumbai remains relatively warm year-round, an inland city like Delhi faces biting cold in January and intense heat in June.

The impact of distance from the sea is further modified by ocean currents and onshore winds. If a coast is adjacent to a warm current, such as the North Atlantic Drift, it will have a significantly milder climate than its latitude would suggest—this is why the UK remains ice-free in winter while parts of Canada at the same latitude are frozen Physical Geography, PMF IAS, Horizontal Distribution of Temperature, p.287. Some climates, like the Laurentian type (Cool Temperate Eastern Margin), serve as an intermediate stage, exhibiting both maritime and continental features depending on the prevailing wind direction Physical Geography, PMF IAS, Climatic Regions, p.460.

Sources: Contemporary India-I, Geography, Class IX, NCERT (Revised ed 2025), Chapter 4: Climate, p.27; Physical Geography by PMF IAS (1st ed.), Horizontal Distribution of Temperature, p.287; Physical Geography by PMF IAS (1st ed.), Climatic Regions, p.460

7. The Function of Longitude: Time and Position (exam-level)

While latitude helps us understand temperature zones, longitude serves a very different primary purpose: it is our global system for measuring time and position. Longitude is defined as the angular distance of a place east or west of the Prime Meridian (0°), measured in degrees from the center of the Earth Physical Geography by PMF IAS, Latitudes and Longitudes, p.242. Unlike latitudes, which are parallel circles of varying lengths, all meridians of longitude are semi-circles of equal length that meet at the North and South Poles Physical Geography by PMF IAS, Latitudes and Longitudes, p.250. By intersecting a specific latitude with a specific longitude, we can pinpoint any location on the planet—for instance, New Delhi sits near 28° N and 77° E Physical Geography by PMF IAS, Latitudes and Longitudes, p.240.

The most fascinating function of longitude is its relationship with time. Because the Earth completes one full rotation of 360° in approximately 24 hours, we can calculate that it rotates 15° every hour, or 1° every 4 minutes. This is why places to the east of the Prime Meridian see the sun earlier and are "ahead" in time, while places to the west are "behind." To maintain global order, the International Date Line was established near the 180° meridian; crossing it results in a change of date by exactly one day Exploring Society: India and Beyond, Locating Places on the Earth, p.24. This longitudinal framework allows for the creation of standardized time zones, preventing the chaos of every town setting its clock solely by the local noon sun.

In the context of world climate classification, it is vital to distinguish between these imaginary lines. While latitude, altitude, and distance from the sea are fundamental controls of climate—affecting temperature and precipitation—longitude itself does not determine a region's climate Certificate Physical and Human Geography, Climate, p.131. A city at 30° E and another at 120° E might have identical climates if their latitudes and altitudes are the same. Longitude tells us when the sun rises, but latitude tells us how hot that sun will be.

Feature	Latitude (Parallels)	Longitude (Meridians)
Direction	North or South of Equator	East or West of Prime Meridian
Primary Function	Temperature & Heat Zones	Time Zones & Position
Length	Decreases toward poles	All are equal in length

Sources: Physical Geography by PMF IAS, Latitudes and Longitudes, p.240; Physical Geography by PMF IAS, Latitudes and Longitudes, p.242; Physical Geography by PMF IAS, Latitudes and Longitudes, p.250; Exploring Society: India and Beyond, Locating Places on the Earth, p.24; Certificate Physical and Human Geography, Climate, p.131

8. Solving the Original PYQ (exam-level)

You've just mastered the fundamental "Climatic Controls" that determine why the Sahara is a desert while the Amazon is a rainforest. This question tests your ability to distinguish between geographic coordinates that directly influence physical variables and those that primarily determine temporal ones. As established in CONTEMPORARY INDIA-I, Geography, Class IX NCERT, there are six major controls of climate: latitude, altitude, pressure and wind systems, distance from the sea, relief features, and ocean currents. This PYQ requires you to identify the outlier that does not belong to this functional group.

To arrive at the correct answer, think about the cause-and-effect relationship each factor has with temperature and moisture. Latitude dictates the angle of solar radiation; Altitude causes temperature to drop via the normal lapse rate (as detailed in FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI NCERT); and Distance from the sea determines the moderating influence of water versus the extreme temperatures of land. However, Longitude is a measure of position relative to the Prime Meridian used for calculating time and longitudinal distance. Because climate zones are distributed horizontally (from the equator to the poles) rather than vertically (from east to west), (B) Longitude has no inherent impact on an area's temperature or rainfall patterns.

A common UPSC trap is to present terms that appear equally "scientific" or "geographical" to confuse the candidate. Students often get distracted by the fact that longitude affects when the sun rises, forgetting that it does not affect how much heat the sun delivers. By remembering the "Big Three" of climate control—Heat Budget (Latitude), Elevation (Altitude), and Continentality (Distance from the sea), as highlighted in Certificate Physical and Human Geography, GC Leong—you can easily isolate the odd one out. Always look for the factor that lacks a direct mechanism for altering atmospheric physics.