Class 9 Social Science Chapter 3: Atmosphere and Climate

The blanket of air surrounding the Earth, held down by gravity and made of gases in varying proportions. It is not merely something we breathe: it filters dangerous radiation, holds warmth in, and is the medium in which all weather and climate occur.

The height of a place above mean sea level, usually measured in metres or feet, with mean sea level counted as zero. Altitude matters throughout this topic because the layers of the atmosphere are distinguished by how temperature and density change with it.

How tightly packed the air is. It is greatest near the Earth's surface, where the weight of everything above compresses it, and it falls steadily as you climb. This is why the upper layers are described as thin.

A layer of ozone gas within the stratosphere that filters the Sun's harmful radiation, including ultraviolet. It is one of two shielding functions the atmosphere performs, the other being the trapping of heat that keeps the planet warm enough to live on.

The atmosphere is a blanket of air surrounding the Earth, pulled down around it by gravity and made of a mixture of gases in various proportions. It shields us from harmful radiation from the Sun, including ultraviolet, and it regulates the Earth's temperature, holding back part of the Sun's energy and preventing it from escaping back into space.

Nitrogen makes up about 78 per cent and oxygen about 21 per cent. Argon stands at about 0.93 per cent, carbon dioxide at about 0.04 per cent and other gases at about 0.03 per cent. Water vapour is treated separately because its amount varies, generally between 0.1 and 0.4 per cent. It also plays a significant role in cloud formation and precipitation.

Temperature decreases with increasing altitude only in the troposphere and the mesosphere. In the thermosphere it rises very rapidly, because the gas molecules there take in the Sun's X-rays and short-wave ultraviolet radiation.

The stratosphere is free of clouds and other weather disturbances, which makes it ideal for flying. It is also the layer containing the ozone gas that shields us by filtering the Sun's harmful radiation, including ultraviolet.

It extends from 80 to 700 kilometres, and temperature in it rises very rapidly with altitude because its gas molecules absorb the Sun's X-rays and short-wave ultraviolet radiation. It helps radio transmission by reflecting radio waves back towards the Earth, the ionosphere being part of it, and the auroras occur within it.

The air above us does exert a significant force. We do not feel it because air presses on us from all sides rather than only from above, and because the pressure inside our bodies is equal to the atmospheric pressure outside, so the two cancel each other out.

The atmosphere is a blanket of air surrounding the Earth, pulled down around it by gravity, and it consists of a mixture of gases in various proportions.

Nitrogen and oxygen are the two primary and most abundant gases, at roughly 78 and 21 per cent. Beyond them lie carbon dioxide, argon, helium, neon, krypton, xenon, ozone and hydrogen in far smaller quantities, with argon at about 0.93 per cent and carbon dioxide at about 0.04.

The atmosphere also carries water vapour and tiny dust particles. Water vapour varies, generally between 0.1 and 0.4 per cent, and although the quantity is small it matters a great deal for cloud formation and precipitation. What the atmosphere is made of itself varies with altitude.

Its importance to life runs in three directions. It shields us from harmful radiation coming from the Sun, including ultraviolet, largely through the ozone held in the stratosphere. It regulates the Earth's temperature, holding back part of the Sun's energy and preventing it from escaping back into space, so that the planet stays warm enough to live on.

And it is central to the Earth's weather and climate systems and affects temperature, humidity and air pressure. Without it there would be no rain, no breathable air and no protection from what the Sun sends towards us.

The atmosphere has a layered structure, and the layers are marked out by how temperature and density change as altitude rises. Air density is highest near the Earth's surface and decreases as you climb.

The troposphere is the lowest layer, averaging about 12 kilometres. Temperature decreases with altitude in it, and it holds the air we breathe along with most of the water vapour and clouds. Nearly all weather phenomena, such as rainfall, fog and hail, occur here, and the tropopause separates it from the layer above.

The stratosphere extends up to 50 kilometres. Being free of clouds and weather disturbances it is ideal for flying aeroplanes, and it contains the layer of ozone gas that filters the Sun's harmful radiation. Its upper boundary is the stratopause.

The mesosphere extends up to 80 kilometres, and temperature decreases with altitude here as well. Most meteorites entering from space burn up in it. These two layers are the only ones in which temperature falls as altitude rises.

The thermosphere extends from 80 to 700 kilometres, and temperature rises very rapidly because its gas molecules absorb the Sun's X-rays and short-wave ultraviolet radiation. It reflects radio waves back to Earth, the ionosphere being part of it, and the auroras occur in it. Above all lies the exosphere, with very thin air, from which light gases such as helium and hydrogen float into space because gravity is weak.

An aurora is the bright, many-coloured lights that appear in the sky near the poles. The word comes from Latin, meaning dawn or morning light, and it is named after Aurora, the Roman goddess of dawn.

Auroras occur in the thermosphere, the layer extending from 80 to 700 kilometres in which temperature rises very rapidly with altitude.

The mechanism begins at the Sun. The solar wind, which is made of charged particles emitted by the Sun, reaches the Earth's atmosphere and is directed towards the magnetic poles. As those particles strike the different gases of the atmosphere, each gas gives off its own colour, and the display is called the Aurora Borealis in the north and the Aurora Australis in the Southern.

The upper layers matter for more practical reasons too. The thermosphere helps radio transmission by bouncing radio waves sent up from the Earth back down to it, and the ionosphere responsible for this is part of that layer, so signals can travel beyond a straight line from the transmitter.

The mesosphere is where most meteorites entering from space burn up, so it acts as a shield, and the exosphere marks the point at which the atmosphere thins so far that light gases escape into space. Every one of these layers matters to the Earth's atmospheric processes and affect weather and climate.

Two descriptions of the same atmosphere at different timescales. Weather covers the hour-to-hour and day-to-day condition and changes quickly. Climate is the average taken over a large area and an extended period, usually thirty years or more, so it changes only slowly.

Energy arriving from the Sun that the Earth catches on its way past. It is the chief control on how temperature is distributed, and because the amount received decreases from the equator towards the poles, so does temperature.

The pressure exerted by the weight of air on the Earth's surface. It falls rapidly with altitude, being highest at sea level. Horizontally it is governed by temperature, which is what links pressure to the weather people actually experience.

Air moving from an area of high pressure to one of low pressure. Winds are named after the direction they blow from, so a wind arriving out of the west is called a westerly rather than an easterly.

Weather means the state of the atmosphere from hour to hour and day to day, and it can vary significantly from one day to the next. Climate gathers all of that together across a wide stretch of country and a long run of years, thirty of them at the least.

The five are temperature, precipitation, humidity, wind and atmospheric pressure. Insolation, the incoming solar energy intercepted by the Earth, is the important factor affecting temperature distribution, and because it decreases from the equator towards the poles, temperature does the same.

In areas with high temperatures the air heats up and rises, which creates a low-pressure area, and low pressure goes with cloudy skies and wet weather. Where temperatures are lower the air is cold and therefore heavy, so it sinks and creates a high-pressure area, which is associated with clear and sunny skies.

Wind is air moving from an area of high pressure to one of low pressure, and it can be gentle or strong. Winds are named after the direction they blow from, so a wind blowing from the west is called a westerly.

A sea breeze blows from sea to land by day, above all in the afternoon, once the land has grown warmer than the sea and a low-pressure region forms over the land. A land breeze blows from land to sea during the night, because land cools faster than the sea. Its speed is low because the difference in temperature and pressure between the two is small.

Winter, from December to early April. Summer or pre-monsoon, from April to June. Monsoon or advancing monsoon, from June to September. Post-monsoon or retreating monsoon, from October to December.

Temperature varies between day and night and across seasons. The important factor affecting its distribution is insolation, the incoming solar energy from the Sun intercepted by the Earth, and because insolation decreases from the equator towards the poles, temperature decreases in the same direction.

Humidity is the presence of water vapour in the air, creating moisture. It arises when water evaporates from land and water bodies, and because warmer air can hold more water vapour, humidity levels rise as temperature does. On a humid day clothes take longer to dry and sweat evaporates more slowly.

Precipitation happens when some part of the atmosphere is saturated with water vapour, which condenses and falls to the Earth under gravity. It includes drizzle, rain, snow, sleet and hail, and the main factors affecting it are prevailing winds, mountains and seasons.

Atmospheric pressure is the pressure exerted by the weight of air on the Earth's surface. It is highest at sea level and falls rapidly with altitude, while horizontally it is governed by temperature: warm air rises to create low pressure, cold air sinks to create high pressure.

Wind is air moving from an area of high pressure to one of low pressure, and it can be gentle or strong. Winds are named after the direction they blow from, so a wind out of the west is called a westerly. Together these five elements account for the weather of any place on any day.

Both are local winds, and both follow from the rule that air moves from a high-pressure area to a low-pressure area.

During the day, especially in the afternoon, the land becomes relatively warmer than the sea. The air over the land heats and rises, forming a low-pressure region above it, while pressure over the cooler sea remains higher. Air therefore begins blowing from the sea towards the land, and this is the sea breeze.

At night the situation reverses. Land cools faster than the sea, so the sea is now the warmer surface and the land the cooler one, and the wind blows from land to sea instead. This is the land breeze.

The land breeze is the gentler of the two, because the difference in temperature and air pressure between the sea and the land at night is small, and wind speed depends on how large that difference is.

Their importance is that they are essential in creating moderate climatic conditions in coastal regions. The daily exchange of air between land and sea evens out the extremes, which is why a coastal town experiences a gentler swing between its hottest and coldest conditions than an inland town at the same latitude.

The climate of India can be broadly classified as tropical monsoon, and the Indian Meteorological Department recognises four distinct seasons.

Winter generally lasts from December to early April, with December and January the coldest months. The average temperature in the north-west is then around 10 to 15 degrees Celsius, rising towards the equator to around 20 to 25 degrees in the south-east of mainland India.

Summer, or the pre-monsoon season, spans April to June, or up to July in north-western India. April is the hottest month in western and southern regions and May in the north, with average temperatures across most of inland India running from 32 to 40 degrees.

The monsoon or advancing monsoon generally spans June to September, dominated by the humid south-west summer monsoon that sweeps across the country in late May or early June. The post-monsoon or retreating monsoon lasts from October to December, and north-western India usually has clear skies in October and November, and the Himalayan states, with their more temperate climate, also experience autumn and spring.

Traditionally, India experiences six seasons rather than four — Vasanta, Grīṣhma, Varṣhā, Śharad, Hemanta and Śhiśhira — each about two months long. These are based on the astronomical division of the twelve months into six parts, and the traditional Indian calendar reflects them in its arrangement of months, although their duration may vary across different parts of the country.

The seasonal reversal in the direction of the wind during a year. The same system blows one way for part of the year and the opposite way for the rest, which is what distinguishes it from a wind that merely varies in strength.

Land warms and cools faster than water does. This single difference is the engine of the whole monsoon: in summer it makes the land hotter than the sea, and in winter it makes the land colder, and the pressure pattern reverses along with it.

A way of cutting the Moon's track across the sky into twenty-seven equal sections, each with a star or cluster attached. Since the Moon takes about twenty-seven days to circle the Earth relative to the stars, it moves through roughly one nakṣhatra a day.

The condition of an economy whose output, incomes and food supply all turn on how one season behaves. India's agriculture depends heavily on monsoon rainfall, so the same event that fills reservoirs in a good year empties them in a poor one.

The monsoon is the wind turning right around partway through the year. The word comes from the Arabic mausim, which literally means season, and it was the Arabs who came to India as traders that gave the phenomenon its name.

It is caused mainly by the unequal heating of land and sea. In summer India's landmass warms up faster than the oceans around it, which creates a low-pressure area over the subcontinent while the cooler Indian Ocean has high pressure. Since winds move from high-pressure areas to low-pressure areas, moist winds blow from the ocean towards the land and bring rainfall.

In winter the Indian landmass cools faster than the oceans, creating high pressure over land and low pressure over the seas. Cold and dry winds therefore blow from land to sea and bring no rain to most of the country. The exception is the eastern coast. There these winds cross the Bay of Bengal, gather moisture and bring rain, especially in Tamil Nadu, Andhra Pradesh and parts of Karnataka.

The monsoon reaches how the day is spent, how people travel, when they celebrate and what work is going, above all in the countryside. Taken together with its effect on farming, it greatly influences the economy, the lifestyle and the livelihoods of people in India.

Weak monsoons can lead to droughts, since agriculture depends on the rain for sowing and growing crops and there is then not enough water in rivers, reservoirs and wells. Excessive rainfall can cause floods, damaging crops, property and infrastructure. What is needed is a sufficient monsoon rather than a maximal one.

Kṛiṣhiparāśhara's main technique was read from where the Moon and the Sun stood against the sky. Varāhamihira, in his Bṛihatsaṁhitā, considered the lunar mansions or nakṣhatras in predicting seasonal rainfall, and both texts describe such methods for every season.

The monsoon is the seasonal reversal in wind direction during a year, and both its phases arise from the same fact: land changes temperature faster than sea.

The south-west or summer monsoon comes off the water onto the land, crossing the Indian Ocean, the Bay of Bengal and the Arabian Sea from June to September. In summer India's landmass warms up faster than the oceans around it, creating a low-pressure area over the subcontinent, while the relatively cooler Indian Ocean has high pressure.

Since winds move from high pressure to low pressure, moist winds blow from the ocean towards the land, and because they have crossed a great deal of open water they arrive loaded with moisture, which falls as rain. This monsoon brings the greater part of all the rain India receives across a whole year.

The north-east or winter monsoon occurs from October to February, when the process runs backwards. The Indian landmass now loses heat faster than the oceans around it, so high pressure builds over the land and low pressure over the seas, so cold and dry winds blow from land to sea.

Because these winds blow off a dry landmass they generally bring no rainfall to most of India. The exception is the eastern coast: on passing over the Bay of Bengal the winds pick up moisture and cause rainfall, especially in Tamil Nadu, Andhra Pradesh and parts of Karnataka, which is why in the south-eastern regions it is the winter season that supplies the rain.

Farming across most of India waits on this rain, because sowing and raising a crop both depend on it — for the sowing and the growing their crops. The arrival of the season therefore sets the timing of the whole agricultural year.

When the season behaves there is enough grown to eat, and water left standing in rivers, reservoirs and wells, so its effects outlast the season by many months. Stored water drawn on through the dry part of the year is water the monsoon delivered.

The influence extends well beyond the fields. The monsoon reaches how the day is spent, how people travel, when they celebrate and what work is going, above all in the countryside, so both the working calendar and the calendar of celebration are arranged around it.

The dependence also carries risk in both directions. Excessive rainfall can cause floods, damaging crops, homes and infrastructure, while weak monsoons can lead to droughts, leaving fields unsown and reservoirs low. What is needed is a sufficient monsoon rather than a maximal one.

Because so much turns on one season, India has long sought to predict it. Kṛiṣhiparāśhara used the positions of the Moon and the Sun, and Varāhamihira the lunar mansions, while today the National Monsoon Mission and Mission Mausam work at the same problem with modern prediction models.

Because crop production so often depended on the seasonal monsoon rains, Indians worked out methods of predicting rainfall a very long time ago, and two texts are named for describing such methods for each season. Kṛiṣhiparāśhara's main technique was read from where the Moon and the Sun stood against the sky. Varāhamihira, in his Bṛihatsaṁhitā, considered the lunar mansions, or nakṣhatras, in predicting seasonal rainfall. A nakṣhatra is one of twenty-seven equal sections into which the Moon's track across the sky is cut, each with a star or cluster attached to it. Since the Moon takes about twenty-seven days to circle the Earth relative to the stars, it moves through roughly one each day, which is why they are described as lunar mansions. The monsoon reached literature as well. Kālidāsa, in the Meghadūtam written around the fifth century CE, mentions the date of the monsoon's onset over central India and traces the path of the monsoon clouds. Even today a great many farming practices in India rest on these ancient methods. The same problem is now approached with different instruments. Under the National Monsoon Mission, the Ministry of Earth Sciences has developed advanced weather and climate prediction models, with the objective of enhancing monsoon predictions over all time frames. Mission Mausam aims to make India a world leader in weather and climate science and to make the nation Weather Ready and Climate Smart, serving agriculture, disaster management and rural development.

A long-term shift in weather patterns — temperature, rainfall and wind — as distinct from the ordinary variation of weather from day to day. What makes it a distinct problem is that it is driven chiefly by human activity rather than by natural cycles.

Gases in the atmosphere that trap heat, including carbon dioxide, methane, nitrous oxide and water vapour. Human activities increase their concentration, and the trapped heat raises global temperatures, which is the mechanism connecting what people burn to how the climate behaves.

All the greenhouse gases sent into the atmosphere because of a person's or an organisation's activities — energy use, transportation, or the production of the goods and services they consume. It converts an abstract global problem into a figure an individual can act on.

A weather system arriving from the west that can bring additional moisture and rain to northern India. In 2025 such disturbances intensified an already heavy monsoon over Punjab, which is how two separate sources of rain came to arrive together.

Climate change means a lasting shift in what the weather typically does with heat, with rain and with wind. It is brought about mostly by human activity — burning fossil fuels, cutting down forests, and industrial pollution that gives off gases such as carbon dioxide into the atmosphere.

Carbon dioxide, methane, nitrous oxide and water vapour. Human activities increase their concentration in the atmosphere, and because these gases trap heat, the result is a rise in global temperatures.

More frequent floods and droughts, the melting of glaciers, rising sea levels and a loss of biodiversity. It also threatens ecosystems and affects human health, agriculture and livelihoods, reaching almost all sections of the population including women and children.

A carbon footprint is the whole quantity of heat-trapping gas that a person's doings put into the air, like energy use, transport, or making goods and services. A student could walk or cycle instead of travelling by private car, and could switch off electrical appliances when they are not in use.

Punjab faced very heavy monsoon rains, which were intensified by western disturbances bringing more moisture and rain. It rained in Himachal Pradesh and Jammu and Kashmir as well, so water came down from the hills, and the Satluj, Beas, Ravi and Ghaggar were running high even before the heavy rains came, so the rivers overflowed.

The river embankments, known as dhūsī bāndh, were weak and old and could not hold back the rising water. People had put up houses and farms right beside the rivers, leaving less natural room into which floodwater could spread safely. Silt and mud had built up in rivers and dams, so they could hold and carry less water. And in some areas flood warnings reached people too late, or reached them in terms too vague to act on, leaving people unprepared.

Climate change refers to a lasting shift in what the weather typically does with heat, with rain and with wind, and the chapter describes it as one of the most urgent challenges the Earth faces today. The word long-term is what separates it from ordinary weather, which varies from day to day without any lasting shift.

It is caused mainly by human activities. The burning of fossil fuels, deforestation and industrial pollution all release gases such as carbon dioxide into the atmosphere.

The mechanism follows from that. These actions increase the greenhouse gases present — carbon dioxide, methane, nitrous oxide and water vapour — and because those gases trap heat, global temperatures rise.

The consequences are already being seen rather than merely predicted. Floods and droughts are becoming more frequent, glaciers are melting, sea levels are rising, and biodiversity is being lost as species cannot adjust quickly enough.

Its reach extends past the environment. Climate change threatens ecosystems, and it also affects human health, agriculture and livelihoods, having a heavy toll on nearly every section of the population, women and children among them. Tackling it requires collective effort: cutting carbon footprints, switching to renewable energy, protecting forests and living sustainably.

Both natural and human-made factors lay behind the Punjab floods, and the chapter sets the two out separately.

Among the natural causes, Punjab faced very heavy monsoon rains in 2025, and these were intensified by western disturbances bringing still more moisture and rain. Rain fell in Himachal Pradesh and Jammu and Kashmir as well as in Punjab, so water came down from the hills in addition to what fell locally.

The major rivers of the state — the Satluj, the Beas, the Ravi and the Ghaggar — were running high even before the heavy rains came. When the additional water arrived, from the hills and from local rainfall together, the rivers overflowed and flooding spread across many parts of Punjab.

Four human-made causes aggravated it. The river embankments, the dhūsī bāndh, were weak and old and could not hold back the rising water in the heavy monsoon rains. People had built houses and farms too close to the rivers, which reduced the natural space into which floodwater could spread safely.

Over time, silt and mud had also built up in rivers and dams, so they could hold and carry less water, and in some areas flood warnings reached people too late, or reached them in terms too vague to act on, leaving people unprepared. All these factors together increased the damage the floods caused.

The floods damaged large parts of the state, including settlements, cropland, dwellings and the roads and bridges that served them, and although water began to recede in some places and relief work went on, the damage overall was devastating.

Many people lost their lives, and thousands were forced out of their homes and into relief camps for safety. Wide stretches of cropland went under, and the paddy standing on them was ruined.

Livestock suffered as well. Bird and milk farms alike were wrecked, and a great many cows, buffaloes and chickens sickened or died, which removes a household's income along with its food.

Roads, bridges, border fences and some public buildings were damaged, and murky standing water led to health problems, such as waterborne diseases spreading, and concerns about sanitation, so the danger outlasted the flood itself. Overall the state suffered heavy economic losses, social disruption and environmental damage.

The lesson the chapter draws is a practical one. The rain was natural and could not have been prevented, but the weak embankments, the building close to the rivers, the silted channels and the late warnings were all decisions that could have gone differently. The event therefore underscores the urgent need for improved flood management and preparedness.

The atmosphere is a blanket of air surrounding the Earth, pulled down around it by gravity and made of a mixture of gases in various proportions. It shields us from harmful radiation from the Sun, including ultraviolet, and it regulates the Earth's temperature, holding back part of the Sun's energy and preventing it from escaping back into space.

Nitrogen makes up about 78 per cent and oxygen about 21 per cent. Argon stands at about 0.93 per cent, carbon dioxide at about 0.04 per cent and other gases at about 0.03 per cent. Water vapour is treated separately because its amount varies, generally between 0.1 and 0.4 per cent. It also plays a significant role in cloud formation and precipitation.

Temperature decreases with increasing altitude only in the troposphere and the mesosphere. In the thermosphere it rises very rapidly, because the gas molecules there take in the Sun's X-rays and short-wave ultraviolet radiation.

Weather means the state of the atmosphere from hour to hour and day to day, and it can vary significantly from one day to the next. Climate gathers all of that together across a wide stretch of country and a long run of years, thirty of them at the least.

The five are temperature, precipitation, humidity, wind and atmospheric pressure. Insolation, the incoming solar energy intercepted by the Earth, is the important factor affecting temperature distribution, and because it decreases from the equator towards the poles, temperature does the same.

In areas with high temperatures the air heats up and rises, which creates a low-pressure area, and low pressure goes with cloudy skies and wet weather. Where temperatures are lower the air is cold and therefore heavy, so it sinks and creates a high-pressure area, which is associated with clear and sunny skies.

The monsoon is the wind turning right around partway through the year. The word comes from the Arabic mausim, which literally means season, and it was the Arabs who came to India as traders that gave the phenomenon its name.

It is caused mainly by the unequal heating of land and sea. In summer India's landmass warms up faster than the oceans around it, which creates a low-pressure area over the subcontinent while the cooler Indian Ocean has high pressure. Since winds move from high-pressure areas to low-pressure areas, moist winds blow from the ocean towards the land and bring rainfall.

In winter the Indian landmass cools faster than the oceans, creating high pressure over land and low pressure over the seas. Cold and dry winds therefore blow from land to sea and bring no rain to most of the country. The exception is the eastern coast. There these winds cross the Bay of Bengal, gather moisture and bring rain, especially in Tamil Nadu, Andhra Pradesh and parts of Karnataka.

Climate change means a lasting shift in what the weather typically does with heat, with rain and with wind. It is brought about mostly by human activity — burning fossil fuels, cutting down forests, and industrial pollution that gives off gases such as carbon dioxide into the atmosphere.