Class 9 Social Science Book Part 1 (Geography) Chapter 3 Notes: Atmosphere and Climate

Class 9 Social Science (Geography) Book Part 1 Chapter 3 Notes (Atmosphere and Climate)

With our notes, we want to convey a message that understanding the atmosphere and climate is essential for every Class 9 Social Science Geography student.

Read the comprehensive Class 9 Geography Chapter 3 Atmosphere and Climate notes designed by expert CBSE teachers to help Class 9 Geography students explore the composition and structure of the atmosphere, layers of the atmosphere, differences between weather and climate, elements of weather, seasons in India, monsoon patterns, and the impact of climate change.

These detailed Geography chapter notes provide clear explanations, important definitions, and easy-to-understand concepts for quick revision.

Before you proceed further, below are the quick details:

• Class: 9
• Subject: Social Science (Geography)
• Chapter Number: 3
• Chapter Name: Atmosphere and Climate
• Book Part: 1

Table of Content

Introduction	Composition and Structure of the Atmosphere
Weather and Climate	Seasons in India
Climate Change	Punjab Floods 2025: A Case Study
Before We Move On

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Introduction

What do you see when you look up at the sky? You might see the floating clouds and the sunshine and feel a breeze as well. All of these are the result of a blanket of air surrounding the Earth, called the atmosphere. It is pulled down around the Earth by gravity and is a mixture of gases in various proportions, vital for the survival of all living beings on the Earth. The atmosphere shields us from harmful radiation coming from the Sun, including ultraviolet radiation. It regulates the Earth’s temperature by trapping some of the Sun’s energy and preventing it from escaping back into space. The atmosphere is a key component of the Earth’s weather and climate systems, influencing factors such as temperature, humidity, and air pressure.

Gravity: It is a fundamental physical force of attraction between objects that have mass or energy, such as the Sun and the Earth. The force of attraction that the Earth’s mass exerts on objects that are on or close to its surface is referred to as Earth’s gravity.

Composition and Structure of the Atmosphere

Composition of the Atmosphere

The Earth’s atmosphere is composed of a mixture of various gases. Nitrogen and oxygen are the two primary and most abundant gases that are essential to life on Earth. Carbon dioxide, argon, helium, neon, krypton, xenon, ozone, and hydrogen are some other gases present in the atmosphere, but they are found in smaller quantities. Besides these, the atmosphere also consists of water vapour and tiny dust particles. The amount of water vapour in the atmosphere varies, but it generally ranges from 0.1 per cent to 0.4 per cent. Water vapour plays a significant role in cloud formation and precipitation. The composition of the atmosphere also varies with altitude.

Structure of the Atmosphere

The atmosphere has a layered structure. These layers are defined on the basis of changes in temperature and density with increasing altitude. The density of air is highest near the Earth’s surface and decreases with altitude. The major layers extending from the Earth’s surface to outer space are illustrated below.

Layer	Description
Troposphere	The troposphere is the most important layer of the atmosphere, with an average height of about 12 kilometres. In this layer, temperature decreases with increasing altitude. The air we breathe exists here, along with most of the water vapour and clouds. Nearly all weather phenomena, such as rainfall, fog, and hail, occur in this layer. The troposphere is separated from the stratosphere by a transition zone known as the tropopause.
Stratosphere	Above the troposphere lies the stratosphere, extending up to 50 kilometres. This layer is ideal for flying aeroplanes because it is free of clouds and other weather disturbances. A notable feature of the stratosphere is that it contains a layer of ozone gas, which shields us by filtering the Sun’s harmful radiation, including ultraviolet radiation. The stratopause marks the boundary between the stratosphere and the mesosphere.
Mesosphere	Above the stratosphere lies the third layer of the atmosphere, the mesosphere. It extends up to a height of 80 kilometres. In this layer, temperature decreases with increasing altitude. Most meteorites entering from space burn up in the mesosphere.
Thermosphere	In the thermosphere, temperature rises very rapidly with increasing altitude, as the gas molecules in this layer absorb the X-rays and short-wave ultraviolet radiation of the Sun. The thermosphere extends from 80 to 700 kilometres. It also helps with radio transmission by reflecting radio waves transmitted from the Earth back towards it. The ionosphere is a part of the thermosphere. Additionally, the northern and southern lights, known as auroras, also occur in the thermosphere.
Exosphere	The uppermost layer of the atmosphere is known as the exosphere, characterised by very thin air. Light gases like helium and hydrogen float into space from this layer due to weak gravity. All these layers play a vital role in the Earth’s atmospheric processes and also affect its weather and climate.

Altitude: The height of a location above mean sea level is called altitude and is usually measured in metres or feet. The mean sea level is considered zero.

Weather and Climate

‘Is it going to rain today?’ ‘Will it be bright and sunny today?’ How often do you find yourself wondering about these questions when you want to go out and play?

The term weather refers to the hour-to-hour and day-to-day conditions of the atmosphere. Hot or humid weather may make one irritable, while pleasant or breezy weather may make one cheerful or even make one plan for an outing. Weather can vary significantly from day to day. The average weather conditions of a place over a longer period of time refer to the climate of the place. Climate refers to the sum total of weather conditions and variations over a large area for an extended period of time, usually thirty years or more.

Elements of Weather and Climate  

Various elements influence weather and climate. The major elements of the atmosphere that impact human life on Earth are temperature, precipitation, humidity, wind, and atmospheric pressure. These elements can change under varying conditions.

Insolation: It is the incoming solar energy from the Sun that is intercepted by the Earth.

Element	Description
Temperature	The temperature of the atmosphere varies not only between day and night but also across seasons, just as summers tend to be hotter than winters. An important factor affecting temperature distribution is insolation. The amount of insolation decreases from the equator towards the poles. Hence, the temperature decreases from the equator towards the poles.
Humidity	When water evaporates from land and different water bodies, it becomes water vapour. When the levels of water vapour in the air are high, this leads to high humidity. Therefore, humidity refers to the presence of water vapour in the air, creating moisture. As the air gets warmer, its capacity to hold water vapour increases, leading to higher humidity levels. On such days, clothes take longer to dry, and sweat evaporates more slowly, leaving us feeling very uncomfortable.
Precipitation	Precipitation occurs when a part of the atmosphere becomes saturated with water vapour, which condenses and ‘precipitates’, or falls on Earth due to gravity. This includes drizzle, rain, snow, sleet, and hail. The main factors that affect precipitation include prevailing winds, mountains, and seasons. When precipitation falls on Earth in liquid form, it is called rain. Rain is the most common form of precipitation and lowers the temperature of a place. A long absence of rainfall results in a dry climate. Most of the groundwater is collected from rainwater.
Atmospheric Pressure	The pressure exerted by the weight of air on the Earth’s surface is called air pressure. As we go higher in the atmosphere, pressure falls rapidly. It is highest at sea level and decreases with altitude. Horizontally, the distribution of air pressure is influenced by the air’s temperature at a given place. In areas with high temperatures, air heats up and rises. This creates a low-pressure area. Low pressure is associated with cloudy skies and wet weather. In areas with lower temperatures, the air is cold. It is, therefore, heavy and sinks, creating a high-pressure area. High pressure is associated with clear and sunny skies. Air always moves from high-pressure areas to low-pressure areas. You can refer to Chapter 8 of the Grade 8 Science textbook Curiosity to learn more about this.
Wind	The movement of air from a high-pressure area to a low-pressure area is called wind. It can be gentle or strong. You can observe the flow of wind as it blows dry leaves down the pavement, gently blows away dust particles, or uproots trees during a storm.

DON'T MISS OUT

Winds are named after the direction they blow from, for example, the wind blowing from the west is called westerly.

Local winds such as the land breeze and the sea breeze, also affect the weather and climate of a place. They are essential in creating moderate climatic conditions in the coastal region.

You may have observed that weather conditions often fluctuate, sometimes even within a single day. However, based on generalised monthly atmospheric conditions, or a common pattern over a few weeks or months—such as the days being cool or hot, windy or calm, cloudy or bright, and wet or dry—the year is divided into seasons.

Seasons in India

The climate of India can be broadly classified as tropical monsoon. The Indian Meteorological Department (IMD) has recognised four distinct seasons in India:

Season	Description
Winter	The winter season generally lasts from December to early April. The coldest months of the year are December and January, when the average temperature in the north-west is around 10–15°C. Temperatures increase towards the equator, reaching around 20–25°C in mainland India’s south-east.
Summer or Pre-monsoon	The summer or pre-monsoon season spans from April to June, or up to July in north-western India. In western and southern regions, the hottest month is April; in northern regions, it is May. The average temperature across most of inland India ranges from 32–40°C.
Monsoon or Rainy Season (Advancing Monsoon)	The monsoon season generally spans from June to September. This season is dominated by the humid south-west summer monsoon, which slowly sweeps across the country in late May or early June. Monsoon rain begins to recede from north India at the beginning of October, and South India typically receives more rainfall during this time.
Post-monsoon (Retreating Monsoon)	The post-monsoon season lasts from October to December. In north-western India, October and November are usually cloudless.

The Himalayan states, being more temperate, experience two additional seasons, autumn and spring.

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Traditionally, India experiences six seasons, each about two months long—spring, summer, monsoon, early autumn, late autumn, and winter. These seasons are based on the astronomical division of the 12 months into six parts. The traditional Indian calendar also reflects these seasons through its arrangement of months.

Table 3.2. Traditional Indian seasons. These seasons and their
duration may vary across different parts of the country.

Seasons (Ṛtu)	Months (According to the Indian Calendar)	Months (According to the Gregorian Calendar)
Vasanta	Chaitra–Vaiśākha	March–April
Grīshma	Jyeṣhṭha–Āṣhāḍha	May–June
Varṣhā	Śhrāvaṇa–Bhādrapada	July–August
Śharad	Āśhvina–Kārtika	September–October
Hemanta	Mārgaśhīrṣha–Pauṣha	November–December
Śhiśhira	Māgha–Phālguna	January–February

Think About It

Hindustani Classical music associates certain rāgas with specific seasons. Find out which rāgas are connected to each season with the help of your elders and teachers.

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Kautilya’s Arthaśhāstra contains records of scientific measurements of rainfall and their practical application in managing the country’s revenue and relief efforts.

Monsoon

The climate of India is strongly influenced by monsoon winds. The sailors who came to India during ancient times were among the first to notice the phenomenon of monsoon. They benefited from the reversal of the wind system as they travelled by sailing ships at the mercy of the winds. The Arabs, who had also come to India as traders, named this seasonal reversal of the wind system ‘monsoon’, derived from the Arabic word mausim, which literally means season.

Don’t Miss Out

Since crop production often depended on seasonal monsoon rains, Indians worked out methods to predict rainfall. Kṛishiparāśhara and the Brihatsaṃhitā describe such methods in every season. Kṛishiparāśhara’s main technique was based on the positions of the Moon and the Sun in the sky. Varāhamihira, in his Brihatsaṃhitā, considered lunar mansions (nakshatras) while predicting seasonal rainfall. Even today, a large number of farming practices in India are based on these ancient methods.

Monsoon winds are seasonal winds. They can be categorised into the south-west and north-east monsoons. The south-west monsoon, also known as the summer monsoon, is characterised by winds blowing from sea to land across the Indian Ocean, the Arabian Sea, and the Bay of Bengal between June and September. It is mainly caused by the unequal heating of land and sea. During summer, the landmass of India heats up faster than the surrounding oceans. This creates a low-pressure area over the Indian subcontinent, while the Indian Ocean remains relatively cooler and has high pressure. Winds move from high-pressure areas to low-pressure areas, so moist winds blow from the ocean towards the land, bringing rainfall. It accounts for most of the rainfall in the country throughout the year.

The winter monsoon, also known as the north-east monsoon, occurs in India from October to February. During this season, the Indian landmass cools faster than the surrounding oceans, creating a high-pressure area over the land and low pressure over the seas.

Monsoon: It refers to the seasonal reversal of wind direction during a year.

Lunar Mansions (nakshatras): Nakshatras are a way of dividing the sky into 27 equal parts along the path travelled by the Moon. Each part is linked to a star or group of stars, but it is really just a fixed section of the sky. The Moon takes about 27 days to go around the Earth relative to the stars, so it moves through one nakshatra each day. That is why they are called “lunar mansions”—it is like the Moon stays in a different “house” in the sky every night.

As a result, cold and dry winds blow from land to sea. These winds generally do not bring rainfall to most parts of India. However, when the north-east monsoon winds pass over the Bay of Bengal, they pick up moisture and cause rainfall on the eastern coast of India, especially in Tamil Nadu, Andhra Pradesh, and parts of Karnataka. Thus, the winter monsoon is important for rainfall in the south-eastern regions of India.

The monsoon plays a vital role in the lives of people in India. Most of India’s agriculture depends on monsoon rainfall, as farmers rely on rain for sowing and growing crops. A good monsoon ensures sufficient food production and water supply in rivers, reservoirs, and wells. The monsoon also affects daily life, transport, festivals, and employment, especially in rural areas. However, excessive rainfall can cause floods, while weak monsoons can lead to droughts. Thus, the monsoon greatly influences the economy, lifestyle, and livelihoods of people in India.

Don’t Miss Out

Kālidāsa, in Meghadūtam, written around the 5^th century CE, mentions the date of the onset of the monsoon over central India and also traces the path of monsoon clouds.

Don’t Miss Out

Under the National Monsoon Mission (NMM), the Ministry of Earth Sciences, Government of India, has developed state-of-the-art weather and climate prediction models. The overall objective of the NMM is to enhance monsoon predictions for India across all time frames.

‘Mission Mausam’ is designed to position India as a global leader in weather and climate sciences. The mission aims to make the nation ‘Weather Ready’ and ‘Climate Smart’, meeting global standards. It aims to improve weather and climate services by ensuring timely and precise observations, modelling, and forecasting information for multiple sectors, including agriculture, disaster management, and rural development.

Climate Change

One of the most urgent challenges that the Earth is facing today is climate change. It refers to long-term changes in weather patterns, such as temperature, rainfall, and wind, caused mainly by human activities, including the burning of fossil fuels, deforestation, and industrial pollution, which release gases like carbon dioxide into the atmosphere. These actions increase greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour in the atmosphere, trapping heat and raising global temperatures. As a result, we are witnessing more frequent floods, droughts, melting glaciers, rising sea levels, and loss of biodiversity. Climate change not only threatens ecosystems but also impacts human health, agriculture, and livelihoods. You may recall that you have read about ‘climate change’ in your Grade 8 Science textbook. What actions can be taken to reduce such changes? It also has a great impact on almost all sections of the population, including women and children. Tackling this issue requires collective efforts—reducing carbon footprints, using renewable energy, protecting forests, and adopting sustainable lifestyles. Every small step counts, and every human being plays a vital role in shaping a healthier and greener future.

Punjab Floods 2025: A Case Study

Section	Details
Overview	In 2025, Punjab experienced severe floods due to heavy monsoon rains and the consequent swelling of the rivers Satluj, Beas, and Ravi. The floods damaged large parts of the state, including villages, agricultural fields, houses, and important infrastructure such as roads and bridges. While the water started to recede in some places and relief operations were carried out, the overall impact was devastating. The state suffered heavy economic losses, social disruption, and environmental damage, underscoring the urgent need for improved flood management and preparedness.
Causes	The floods in Punjab resulted from both natural and human-made factors. Natural Causes: In 2025, Punjab faced very heavy monsoon rains, which were intensified by western disturbances that brought even more moisture and rain. It rained not only in Punjab but also in Himachal Pradesh and Jammu and Kashmir. The major rivers of Punjab—the Satluj, the Beas, the Ravi, and the Ghaggar—were already flowing high before the heavy rains began. When additional rain fell, water from the hills and local rainfall caused the rivers to overflow, leading to severe flooding in many parts of Punjab. Human-made Causes: The floods were further aggravated by weak and old river embankments, or dhusi bandhs, which could not stop the rising water during heavy monsoon rains. People had also built houses and farms too close to the rivers, reducing the natural space where floodwater could spread safely. Over time, silt and mud had collected in rivers and dams, reducing their capacity to hold and carry water. In some areas, flood warnings came late or were not clearly communicated, leaving people unprepared. All these factors together increased the damage caused by the floods.
Effects of the Floods	Many people lost their lives in the floods. Thousands of people had to leave their homes and move to relief camps for safety. Large areas of farmland were covered with water, and crops such as paddy were severely damaged. Poultry and dairy farms were damaged or destroyed. Many animals, including cows, buffaloes, and chickens, became sick or died. Roads, bridges, border fences, and some public buildings were also damaged. Murky standing water caused health problems, including the spread of waterborne diseases and sanitation concerns.
Classroom Discussion	To what extent did natural factors cause these floods compared with human activities? Do you think better planning could have reduced the damage? How? What are the guidelines for flood management according to the National Disaster Management Authority (NDMA)? What role can students and young people play in helping with disaster preparedness?

Before We Move On

• The Earth’s atmosphere is made up of different gases, mainly nitrogen and oxygen, along with small amounts of other gases, water vapour, and dust. Together, they support life and help form clouds and cause rainfall.
• The atmosphere is made up of different layers, namely the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. These layers are divided based on changes in temperature and air density as we go higher above the Earth’s surface. Weather refers to daily atmospheric conditions, while climate is the average weather of a place over a long period of time.
• India has a tropical monsoon climate, and the Indian Meteorological Department (IMD) divides the year into four main seasons: winter, summer, monsoon, and post-monsoon.
• Climate change is the long-term change in weather caused mainly by human activities such as burning fuels and cutting down trees, which leads to global warming and extreme weather conditions.
• We can reduce our carbon footprint by saving energy, using renewable energy sources, planting trees, and living in more eco-friendly ways.

The End

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A List of Book Part 1 Notes:

Chapter 1  |  Chapter 2  |  Chapter 3  |  Chapter 4 (Coming Soon)  |  Chapter 5 (Coming Soon)  |  Chapter 6 (Coming Soon)  |  Chapter 7 (Coming Soon)  |  Chapter 8  |  Chapter 9 (Coming Soon)  |  Chapter 10 (Coming Soon)  |  Chapter 11 (Coming Soon)  |  Chapter 12 (Coming Soon)

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A List of Book Part 2 Notes:

Chapter 1  |  Chapter 2 (Coming Soon)  |  Chapter 3 (Coming Soon)  |  Chapter 4 (Coming Soon)  |  Chapter 5  |  Chapter 6 (Coming Soon)  |  Chapter 7 (Coming Soon)  |  Chapter 8 (Coming Soon)  |  Chapter 9 (Coming Soon)  |  Chapter 10 (Coming Soon)  |  Chapter 11 (Coming Soon)  |  Chapter 12 (Coming Soon)