Maarg Manthan · Topic 5.5

Factors Controlling the Distribution of Temperature

Geography › Climatology · Topic 5.5

The temperature at a place depends mainly on latitude, which decides the angle of the Sun's rays and the length of day, and on altitude, distance from the sea, ocean currents, prevailing winds, cloud cover, the nature of the surface and the slope of the land. Together they explain why places on the same latitude can have very different temperatures, and why a high mountain near the equator can be cold.

8 min read · UPSC Prelims · Geography · Climatology

At a Glance

Latitude Angle of rays and day length
Altitude Falls about 6.5 degrees per km
Distance from sea Maritime versus continental climate
Ocean currents Warm and cold currents change coasts
Local factors Winds, cloud, surface, slope
Exam link UPSC Prelims, Geography: Climatology

Where Does It Fit?

This topic follows the heat balance and explains why temperature differs from place to place. It adds the horizontal pattern shown by isotherms, and prepares the topic on temperature inversion, in which the vertical pattern is reversed. Previous topic: Heat Balance of the Atmosphere: Conduction, Convection, Advection, Terrestrial Radiation, Albedo. Next topic: Inversion of Temperature.

Why Does Temperature Vary from Place to Place?

In short: latitude sets the basic heat, and altitude, sea, currents, winds and surface adjust it.

The air is heated mainly from below, by contact with the warmed surface, and so the temperature of a place depends on the amount of insolation received and on how the surface and atmosphere handle it, as in Heat Balance of the Atmosphere: Conduction, Convection, Advection, Terrestrial Radiation, Albedo. The main factors affecting temperature are described below. The air temperature is measured at a standard height of about 1.2 to 2 m above ground, in the shade, and the daily mean is the average of the highest and lowest values. The daily range is the difference between the day’s maximum and minimum, and the annual range is the difference between the warmest and coolest months.

How Does Latitude Matter?

Latitude is the most important factor. The amount of insolation received depends on the angle of the Sun’s rays and the length of the day. Near the equator the Sun’s rays fall nearly vertically and cover a small area, giving high temperatures, while near the poles they are slanting, spread over a larger area, and pass through more atmosphere, so less heat is received per unit area. Hence temperature generally decreases from the equator to the poles, as shown by the heat zones in Latitude and Longitude – Important Parallels and Meridians. Seasonal variation also increases with latitude, as in Equinoxes and Solstices (Summer Solstice, Winter Solstice, Vernal and Autumnal Equinox).

How Do Altitude, Sea and Ocean Currents Matter?

Altitude: the atmosphere is heated mainly from the ground, so temperature falls with height at the normal lapse rate of about 6.5 degrees Celsius per km. Thus hill stations such as Shimla, Ooty and Darjeeling are cooler than the plains nearby, and Quito, on the equator at about 2,850 m, has a cool spring-like climate. Snow lies on Kilimanjaro, near the equator.
Distance from the sea (continentality): water heats and cools slowly because of its high specific heat, and land heats and cools quickly. Places near the sea have a maritime climate with a small annual range, mild winters and cooler summers, as at Mumbai. Places far from the sea have a continental climate with extreme heat and cold, as at Delhi, Nagpur and Verkhoyansk in Siberia, which has an annual range of over 60 degrees.
Ocean currents: warm currents raise coastal temperatures, and cold currents lower them. The warm North Atlantic Drift keeps the ports of western Europe, such as northern Norway, ice-free in winter, and the cold Labrador and Humboldt currents cool the coasts of Newfoundland and Peru. The effects are in Major Ocean Currents of the World and Their Effects.
Prevailing winds: winds from the sea bring moderate temperatures, and winds from the land bring extremes. The western coasts in the westerlies have a mild climate, and the interiors have a harsh one.

What Are the Other Factors?

Factor	Effect
Cloud cover and humidity	Clouds reduce daytime heating by reflecting insolation and reduce night cooling by trapping heat, so cloudy places have a smaller daily range
Nature of the surface (albedo)	Snow and light sand reflect more; dark soils, forests and cities absorb more
Aspect of slope	In the northern hemisphere, south-facing slopes get more sun and are warmer than north-facing slopes; this is evident in the Himalaya, where settlements and orchards lie on sunny slopes
Relief and mountain barriers	Mountains block cold or warm winds; the Himalaya shield India from cold Central Asian winds
Vegetation and soil moisture	Forests moderate temperature through shade and transpiration; dry bare soil heats quickly
Urbanisation	Cities are warmer than surroundings, forming urban heat islands, because of concrete, asphalt and waste heat

As an analytical point, the factors do not act alone but interact, so a good answer on any place combines them: the temperature of a hill station depends on its latitude and altitude, and also on its distance from the sea and its slope, and the Himalayas, for instance, alter regional temperature patterns in ways beyond altitude alone.

How Can These Factors Be Seen on a Map?

Lines joining places of equal temperature are called isotherms, and on a map they trend east-west over the oceans but bend over the continents because of the differences in heating of land and sea. The patterns they show are described here, and the temperature falls with height are covered in Inversion of Temperature.

How Is Temperature Shown on Maps?

In short: isotherms are lines that join places of equal temperature, reduced to sea level so that altitude does not mislead.

The horizontal distribution of temperature is shown by isotherms, lines joining places having the same temperature at a given time, corrected to sea level so that the effect of altitude is removed and the effect of other factors is seen. Where isotherms are close together, the temperature changes quickly, and where they are far apart, it changes slowly. If the Earth were uniform, isotherms would run parallel to the latitudes. In reality they bend because of differences in the heating of land and water, and the effect of ocean currents. Isotherms are drawn for the whole year or for the extreme months of January and July.

What Are the January and July Patterns?

The January isotherms and the July isotherms show the seasonal shift of heat between the hemispheres.

Feature	January	July
Season	Winter in the north, summer in the south	Summer in the north, winter in the south
Thermal equator	Shifts south of the geographic equator	Shifts north, to about 10 to 20 degrees north
Isotherms over the northern continents	Bend equatorward over land, which is very cold; bend poleward over oceans, which are warmer	Bend poleward over land, which is hot; bend equatorward over oceans, which are cooler
Southern hemisphere	Isotherms are straighter, since there is mostly ocean	Straight and widely spaced
Hot spots	Australia, southern Africa, Argentina	Sahara, Arabia, northern India, southwestern USA
Cold spots	Siberia, northern Canada	Antarctica

The North Atlantic Drift makes the isotherms bend sharply poleward over the northeast Atlantic in winter, so that northern Europe is far warmer than other places at the same latitude, such as Labrador. The southern hemisphere has more water and so has smaller seasonal swings.

What Is the Thermal Equator and the Annual Range of Temperature?

The thermal or heat equator is the line joining the places of highest mean temperature in each meridian. It does not coincide with the geographic equator, since land heats more than sea, and the northern hemisphere has more land. It lies at about 5 degrees north on average, and shifts to about 10 to 20 degrees north over the continents in July.

The annual range of temperature, the difference between the warmest and coolest month, is small near the equator, often only a few degrees, and increases poleward, but it is largest in the interiors of the large landmasses in the middle and high latitudes. Verkhoyansk in Siberia has an annual range of over 60 degrees. The range is much smaller over the oceans and on the western margins of continents.

Why Is This Topic Important?

Concepts Continentality and currents
India Altitude and hill stations
Application Explains regional climates

What Came Next?

The next topic explains temperature inversion, in which the air near the ground is colder than the air above. Next topic: Inversion of Temperature.

Key People and Terms

Continentality Inland effect on temperature
Annual range Difference between warmest and coolest months
Isotherm Line of equal temperature
Lapse rate Fall of temperature with height
Urban heat island City warmer than surroundings
Aspect Direction a slope faces

Exam Corner

Points to Remember

Latitude is the most important factor.
Temperature falls 6.5 degrees per km.
Land heats and cools faster than water.
Warm currents raise coastal temperatures.
Isotherms join places of equal temperature.

Do Not Confuse With

Maritime and continental climate Small versus large range
Warm and cold currents Raise versus lower coastal temperature
Daily range and annual range One day versus one year

Memory Hook

Latitude leads, altitude lowers, sea softens, currents shift, slope and cloud adjust.

Mains Angle

Questions ask for factors with examples. These points add depth.

Primary Latitude and altitude
Sea Continentality and currents
Local Slope, surface, cities

A Question You May Face

An original practice question, not a past paper question.

“Explain the factors that influence the distribution of temperature at the surface of the Earth.”

How to Answer

Latitude Sun’s rays.
Altitude Lapse rate.
Sea and currents Moderation.
Local Slope and surface.

GS Relevance

Prelims: factors, continentality, ocean current effects. GS Paper 1: climatology.

Frequently Asked Questions

What are the main factors affecting temperature distribution?

The main factors are latitude, altitude, distance from the sea, ocean currents and prevailing winds, along with cloud cover, the nature of the surface, the aspect of the slope, mountain barriers, vegetation and urbanisation. Latitude is considered the most important.

How does altitude affect temperature?

Temperature falls with height at the normal lapse rate of about 6.5 degrees Celsius per km, because the atmosphere is heated mostly from the ground and the air thins with height. This is why hill stations such as Shimla and Ooty are cooler than the plains.

What is continentality?

Continentality is the effect of distance from the sea on climate. Land heats and cools faster than water, so places far from the sea have hot summers and cold winters with a large annual range, while coastal places have moderate temperatures and a small range.

How do ocean currents affect temperature?

Warm ocean currents raise the temperature of the coasts that they pass, and cold currents lower it. The warm North Atlantic Drift keeps the ports of northwest Europe ice-free in winter, while the cold Humboldt Current cools the coast of Peru and Chile.

Why do south-facing slopes in the northern hemisphere get warmer?

South-facing slopes in the northern hemisphere receive the Sun's rays at a more direct angle and for longer than north-facing slopes, so they get more insolation and are warmer and drier. In the Himalaya, this is why villages, crops and orchards are often on sunny slopes.

PYQ Practice — Statement Analysis

1 Latitude is the most important factor affecting temperature.

True

It decides the angle of the Sun's rays.

2 Coastal areas have a larger annual temperature range than inland areas.

False

Coastal areas have a smaller range.

3 Temperature normally falls with altitude in the troposphere.