Class 8 Science Chapter 13: Earth, Our Unique Planet

One Planet Out of Eight

Eight planets travel around the Sun, and so far only one of them is known to carry anything alive. That one is under your feet. The question worth asking is not whether Earth is special but what exactly makes it so, because the answer turns out to be a short list of ordinary physical facts.

The Skin on an Apple

Everything living sits on the crust, the solid outer shell of rock and soil. Set against the whole planet the crust is astonishingly thin - about as thin, in proportion, as the skin on an apple. All of farming, all of building and every creature that has ever walked belong to that skin.

Eight Neighbours, Two Families

The eight planets do not form one kind of object. The four nearest the Sun have solid ground, and the four beyond them are enormous balls of gas. The split is sharp enough that the two groups are usually named separately rather than treated as members of a single list.

The Rocky Four

Mercury, Venus, Earth and Mars are the rocky planets. Each has a surface you could stand on, and each is small next to the giants further out. Earth sits third in this group, which puts it neither closest to the Sun nor far away from it.

The Gas Giants

Jupiter, Saturn, Uranus and Neptune are made largely of gas. There is no ground to land on, only thickening layers of gas as you descend. They are also far colder, because the Sun’s warmth has spread thin by the time it reaches them.

Nearest Is Not Hottest

You would expect the planet nearest the Sun to be the hottest. It is not. Mercury averages roughly 170 degrees Celsius, which is fierce, and Venus - one step further out - averages about 450. Distance from the Sun is clearly not the only thing that sets a planet’s temperature.

What Venus Does With Its Air

Venus is wrapped in a thick blanket of carbon dioxide. Sunlight gets in, and the heat that the surface then gives off struggles to get back out. Heat arrives faster than it leaves, so it piles up. That is the greenhouse effect, and on Venus it has run far enough to melt lead.

Mercury Has Almost No Air

Mercury has the opposite problem. It is too small to hold on to a decent atmosphere, so whatever heat it gathers by day escapes freely. Being close to the Sun makes it hot; having no blanket keeps it from becoming hotter still. Two planets, two different reasons.

Mars, Cold and Thin

Mars lies just beyond Earth. Its atmosphere is about a hundred times thinner than ours, so it holds almost no heat, and its surface is bitterly cold. It is close enough to be interesting and bare enough to show what Earth would be without its air.

A Twin That Is Not a Twin

If you measured only size, Venus and Earth would look like a matched pair: take Earth’s radius as one and Venus comes out at about 0.95. Yet one is temperate and the other is an oven. Size alone decides very little, which is worth remembering before calling any planet Earth-like.

Fifteen Degrees

Earth averages about 15 degrees Celsius. Written down it sounds unremarkable, and that is exactly the point: it is the one figure on the list that is neither extreme. Nothing on Earth has to survive 450 degrees or a hundredfold thinner air.

The Blue Planet

Because 15 degrees sits between freezing and boiling, water on Earth can stay liquid, and liquid water covers most of the surface. Seen from space the planet reads as blue with white streaks of cloud, which is where the name comes from. The colour is a direct report of the temperature.

Water Needs a Temperature

Water is the common thread. Too cold and it locks up as ice; too hot and it boils away into the air. Only a narrow band of temperature keeps it pourable, and life as we know it has never been found without water in that pourable state.

Why the Question Matters

Asking what makes Earth suitable is not idle curiosity. Every answer is also a warning, because each condition can be pushed. Venus shows what a carbon dioxide blanket can do if it grows thick enough, and that is a planet, not a thought experiment.

What to Carry Forward

Hold on to three things. Eight planets, four rocky and four gaseous. Nearest is not hottest, because an atmosphere can trap heat. And Earth’s ordinary 15 degrees is what lets water stay liquid, which is what makes the planet look blue from outside.

Scenario:

A newspaper reports that astronomers have found a planet "almost exactly the size of Earth" around another star, and the headline calls it a second Earth. A class is asked whether the headline is justified. One pupil points out that the report gives the planet’s radius and its distance from its star but says nothing at all about its atmosphere. Another says that if the size matches, the rest will follow. The teacher writes three numbers on the board: Venus at 0.95 of Earth’s radius, Venus at about 450 degrees, and Earth at about 15.

Analysis:

The three numbers settle it. Venus is so nearly Earth’s size that by radius alone the two would be reported as a matched pair. And yet one averages about 15 degrees and the other about 450 - hot enough to melt lead. The difference is not size and not even distance, since Venus is only one step nearer the Sun. It is the thick carbon dioxide atmosphere, which lets sunlight in and holds back the heat the surface gives off, so heat accumulates. The first pupil is therefore right that the missing information is the important information. A size and an orbit tell you what reaches the planet; only the atmosphere tells you how much of it stays. Until that is known, "a second Earth" is a headline rather than a finding.

Activity:

Find a news report about a newly discovered planet and list which of the three facts - size, distance and atmosphere - it actually gives.

Title:

Try it at home: a jar that holds its heat

Safety:

Glass in strong sunlight gets hot, so lift the jars with a cloth and keep the thermometers away from the glass wall.

What You Notice:

The closed jar climbs higher in the sun and cools more slowly in the shade, because the trapped air keeps its heat in. That is the same mechanism, at a kitchen scale, that makes Venus hotter than Mercury even though Mercury is nearer the Sun.

Venus turns so slowly that a single day there lasts longer than its whole year, which is one of the few things about it that has nothing to do with its heat.

Lead melts at about 328 degrees Celsius, so a lump of it left on the surface of Venus would not stay solid for long.

Because the gas giants have no solid surface, a spacecraft sent to one of them cannot land in any ordinary sense; it can only descend until the pressure ends the mission.

Rocky four, gassy four — Count outwards. The first four have ground under them; the next four are gas all the way down. The line falls exactly in the middle of the eight.

Nearest is not hottest — Mercury is closer and Venus is hotter. The difference is the blanket: Venus keeps its heat, Mercury lets it go.

Three Conditions, Not One

Earth is liveable because of three separate things, and no one of them would be enough on its own. Where it sits, how big it is, and the magnetic field it generates. Take any one away and the planet would be a very different place.

The Goldilocks Zone

A star warms the space around it, and there is a band of distances where the temperature is neither too high nor too low for water to stay liquid. That band is called the habitable zone, or the Goldilocks zone after the story about porridge that was neither too warm nor too chilly.

Why Water Decides the Zone

The zone is defined by water because liquid water is the one thing every known living process needs. Too close to the star and water boils away as vapour; too far and it locks up as ice. Only inside the band does it stay pourable for long stretches of time.

Venus Inside, Mars at the Edge

Earth sits comfortably inside the band. Venus is too close for comfort and its water is long gone. Mars lies near the outer edge, which is why it is such an interesting case: there is evidence that liquid water once ran across its surface, even though none flows there now.

A Nearly Circular Orbit

Being at the right distance is not quite enough, because a planet’s distance can change as it goes round. Earth’s orbit is very nearly a circle, so the amount of sunlight it receives hardly varies through the year.

Why the Shape of the Orbit Matters

Imagine a long stretched orbit instead. The planet would roast at one end of its year and freeze at the other, and water would swing between vapour and ice. A near-circular path keeps the supply of warmth steady, which is what lets conditions hold rather than merely occur.

Big Enough to Keep Its Air

A planet holds its atmosphere by gravity, and gravity depends on how much planet there is. Earth has enough pull to keep a deep layer of gases from drifting off into space, which is why we have air to breathe and a blanket that moderates the temperature.

What Mars and Mercury Lost

Mars is smaller than Earth, its pull is weaker, and its atmosphere is about a hundred times thinner than ours. Mercury is smaller still and has almost no atmosphere at all. The pattern is clear: less planet means less grip, and less grip means less air.

And Not Too Big Either

The size has an upper limit too. On a much larger planet gravity would be so strong that a body would be crushed under its own weight, and moving about would be impossible for anything built the way we are. Earth is big enough to hold air and small enough to walk on.

Ozone, Oxygen With Three Atoms

High in the atmosphere there is a form of oxygen whose particles carry three atoms instead of the usual two. It is called ozone, and although there is very little of it, it does a job nothing else does.

What Ozone Stops

Sunlight includes ultraviolet rays, which damage living tissue. Ozone absorbs most of them before they reach the ground. Without that layer the surface would receive a dose that would make life on land extremely difficult, so a thin trace of gas protects everything below it.

A Compass Needle and a Core

Deep inside Earth there is molten iron, and it moves. That movement generates a magnetic field which reaches far out beyond the atmosphere. A compass needle swinging to north is the everyday evidence of something happening thousands of kilometres below.

What the Magnetic Field Turns Away

The Sun throws out a stream of high-energy particles, and more arrive from deep space. Both would strip away the atmosphere and damage living things. The magnetic field deflects most of them, so the planet is shielded before its air is even reached.

Mars Without a Shield

Mars no longer generates a magnetic field worth the name, and it has very little atmosphere left. The two facts are related, which is part of why Mars is studied so closely. India sent its own spacecraft to Mars in 2013, and it worked for years longer than planned.

Three Conditions, One Planet

So: a distance that keeps water liquid, an orbit round enough to keep that distance steady, a size that holds air without crushing what walks on it, ozone against ultraviolet, and a magnetic field against the particles. Every one is needed, and Earth happens to have them all.

Scenario:

A school team is asked to plan a human settlement on Mars and to list what must be recreated from Earth. The first draft says that since Mars is in the habitable zone and has a solid surface, the settlers will mainly need food and water. A second pupil objects that the draft has ignored the air entirely. A third points out that the plan says nothing about radiation. The teacher asks the team to rank the problems by how hard each would be to solve, rather than simply listing them.

Analysis:

The first draft has used only one of the three conditions. Mars is indeed inside the habitable zone, though near its outer edge, which is why liquid water once ran there. But Mars is smaller than Earth, so its gravity is weaker and its atmosphere is about a hundred times thinner than ours - air is therefore a problem the plan cannot skip. Worse, Mars no longer generates a magnetic field worth the name, so the high-energy particles streaming from the Sun arrive at the surface instead of being deflected. And they are also why so little air is left. Ranked by difficulty, air and water can be carried or made in a sealed habitat, but a planet-wide magnetic field cannot be manufactured at all. The settlers would have to shelter from the particles rather than stop them.

Activity:

List the three conditions in this topic and write beside each one whether a sealed habitat on Mars could supply it.

Title:

Try it at home: find the field with a floating needle

Safety:

Needles are sharp and magnets should be kept well away from phones, cards and any screen.

What You Notice:

The needle settles to the same direction however you turn the bowl, because it is responding to Earth’s own magnetic field. That field is generated by molten iron moving thousands of kilometres below you. And it is what deflects the high-energy particles arriving from the Sun.

India’s Mars Orbiter Mission, launched by ISRO in 2013, reached Mars at the first attempt and kept working for years beyond the few months it was designed for.

A compass needle settling to north is driven by molten iron moving thousands of kilometres beneath your feet, which makes it one of the few household objects that reports on the core.

Ozone is such a small part of the atmosphere that if it were all brought down to the surface it would make a layer only a few millimetres deep.

Place, size, shield — Three conditions in that order. Where the planet is, how big it is, and what protects it. Lose any one of the three and the planet stops being liveable.

Goldilocks: not too hot, not too cold — The zone is named after the porridge. The test is always the same one - can water stay liquid here?

Four Systems, One Planet

Having the right conditions is one thing; keeping life going day after day is another. Earth does that through four systems that work together - the air, the water, the solid ground and life itself. Each is usually given its own name, and none of them works alone.

The Atmosphere

The atmosphere is that envelope of gases wrapped around the planet. It is held in place by gravity, it moderates the temperature by day and by night, and it is where weather happens. Everything that breathes depends on what is in it.

What the Air Does

Animals take oxygen from the air and return carbon dioxide. Plants take carbon dioxide and give back oxygen. Nitrogen, the most plentiful gas of all, ends up in the compounds that living things are built from. The same mixture serves several completely different purposes.

The Hydrosphere

All the water on the planet taken together - oceans, rivers, lakes, ice and the moisture in the ground - is called the hydrosphere. Water dissolves and carries substances, which is how nutrients travel into a root and around a body.

Seventy Per Cent Water

Water covers roughly seventy per cent of Earth’s surface, which is why the planet looks blue from space. No living thing we know of manages without it, and most of a living body is water by weight.

Sunlight, the Energy Supply

Almost all the energy in living systems arrives as sunlight. Plants capture it and store it as food, animals eat the plants, and other animals eat those animals. Trace any meal backwards far enough and it ends at the Sun.

The Geosphere

The geosphere is the solid part of the planet - its rocks, soil and minerals. It is the floor everything stands on, the source of every mineral we use, and the store from which plants draw what they need to grow.

How Rock Becomes Soil

Rock does not stay rock. Heat, cold, wind, water and roots break it slowly into smaller and smaller pieces. Mixed with the remains of dead plants and animals, those pieces become soil - which is why soil is partly mineral and partly once-living.

Nutrients From Rock and Remains

Soil supplies nutrients such as nitrogen and potassium. Some come from the breakdown of rock and some from decayed remains, and plants absorb them through their roots. A soil stripped of these does not grow much, however much water it is given.

Geodiversity

Just as there is a variety of living things, there is a variety of non-living ground: mountains, valleys, deserts, plains, different rocks and different soils. That variety is called geodiversity, and it is the reason one region grows rice and another grows millet.

The Biosphere

The biosphere is every living thing on the planet taken together - plants, animals and the microorganisms you cannot see. It reaches from deep soil to high air, and it is thin compared with the planet but present almost everywhere on its surface.

Who Does What in the Biosphere

Plants make food and release oxygen. Animals eat, move material about and pollinate. Microorganisms break down what dies, returning its nutrients to the soil. Remove any one of those three jobs and the other two begin to fail within a season.

The Spheres Are Connected

The four systems are not separate compartments. Rain moves water from the atmosphere into the geosphere and the biosphere. Plants move carbon dioxide out of the air. Rivers carry soil into the sea. Anything that changes one system is already changing the others.

Cut a Forest and Watch

Clear a large patch of forest and several things follow. Less water is returned to the air, so local rainfall can drop. Bare soil washes away in the first heavy rain. Fewer trees take in carbon dioxide, so the air quality nearby worsens. One action, four systems.

Balance Is the Whole Point

Life is not sustained by any single system but by the balance between them. Air without water sustains nothing; soil without the microorganisms that build it would stay bare rock; water with no sunlight reaching it grows no plants. The four hold one another steady, and that steadiness is what makes the planet liveable year after year rather than only in a good season. It is also the part most easily damaged. A farmer, a factory or a city does not set out to change the atmosphere or the rivers, but every large action reaches further than the system it was aimed at. Knowing which systems a decision touches is the whole point of naming them, and it is where the next topic begins.

Scenario:

A village stream runs clear for as long as anyone can remember. Two years after a large patch of hillside forest above it is cleared for building, villagers notice three changes. The stream runs brown after every heavy rain. The fields nearest the cleared slope need more fertiliser than they used to. And several people say the afternoon showers that used to be reliable in that valley have become patchy. A panchayat meeting is told that these are three separate problems with three separate causes.

Analysis:

They are one problem seen in three systems. Clearing the forest removed the roots that held the hillside soil. So each heavy rain now carries soil downhill - which is why the stream runs brown, since the brown is the soil itself. The same loss explains the fertiliser: the layer being washed away is the part that held the nitrogen and potassium, so what is left supplies less and has to be topped up. And the trees were returning water to the air, so with fewer of them less water is available to fall again nearby, which fits the patchy showers. One action in the geosphere and the biosphere has produced effects in the hydrosphere and the atmosphere. Planting the slope again addresses all three at once.

Activity:

Walk to a bare slope and a planted slope after rain and compare how cloudy the water running off each one is.

Title:

Try it at home: two jars and a bare slope

Safety:

Keep the trays on a washable surface and pour gently, since muddy water splashes further than it looks.

What You Notice:

The water from the bare slope is far muddier and leaves a thick layer of soil in the glass. Meanwhile the grassed slope gives much clearer water. The roots are holding the soil in place, which is exactly what is lost when a hillside is cleared.

Nitrogen is the most plentiful gas in the air by a wide margin, and yet most living things cannot use it straight from the atmosphere at all.

Soil is partly mineral and partly once-living: broken rock mixed with the remains of plants and animals that have decayed into it.

Most of the weight of a living body is water, which is why no organism we know of manages without the hydrosphere.

Air, water, ground, life — Four systems in that order: atmosphere, hydrosphere, geosphere, biosphere. Say them outwards from the sky to the rock and then back to what lives between.

Bio is alive, geo is not — Biodiversity counts living kinds; geodiversity counts landforms, rocks and soils. The prefix tells you which one a question is about.

Why Reproduction Is Not Optional

Every living thing eventually dies. If plants and animals did not produce new individuals, each kind would simply run out and life on Earth would end. Reproduction is what keeps each kind going, and that is why it belongs in a chapter about what makes this planet liveable.

Instructions Inside Every Cell

A cow has a calf and a cat has kittens because parents pass on instructions telling a single cell how to develop. These instructions are called genes, and a set of them sits in each and every cell of the body. Think of a very detailed manual kept in each room of a house.

Why a Calf Becomes a Cow

Different pages of the manual deal with different things: how to make blood, how to form bone, how to build muscle or skin. Because the calf received a cow’s manual, it develops into a cow and nothing else. The resemblance is not a coincidence; it is a copy of instructions.

Similarity and Variation

Here is the puzzle. The same process produces offspring that clearly resemble their parents and offspring that are clearly not identical to them. Two kittens from one litter differ in colour and size. So reproduction delivers similarity and difference at the same time.

Small Changes That Help

The instructions passed on are not always copied exactly, and sometimes a small change turns out to be useful in a new setting. Camels came to have humps that store fat, which suits a desert. Some bacteria have become resistant to antibiotics, which is a change that helps them persist.

Two Kinds of Reproduction

There are two kinds, and the difference is in how many parents are involved. Asexual reproduction works from one parent only, and the individuals it makes carry instructions identical to its own. Sexual reproduction brings the instructions of both parents together into one new set.

Asexual: One Parent, Exact Copies

With one parent there is nothing to mix, so the offspring carry the same instructions as the parent. That makes asexual reproduction fast and reliable, and it also means the offspring are no better suited to a changed setting than the parent was.

Vegetative Propagation

Many plants grow a whole new plant from a piece of the old one - a leaf, a stem or a root planted in soil. This is called vegetative propagation. A money plant cutting, the eyes of a sprouted potato and a piece of ginger all do it, and bamboo and sugarcane spread this way too.

Microbes and Simple Animals

It is not only plants. Single-celled organisms such as bacteria and amoeba divide into two identical individuals. Algae can regrow from small cut pieces. Hydra grows buds on its body that break off and become new individuals, and planaria, a flatworm, can regrow from a fragment.

Sexual: Two Parents, Mixed Instructions

In sexual reproduction two parents contribute, usually called male and female. It is obvious in animals, but a flower carries male parts and female parts too, and even some microorganisms such as yeast have two mating types that behave like two parents.

Gametes Carry Half

If both parents passed on a full set of instructions, the offspring would have double, and the amount would keep doubling every generation. It does not, because each parent makes special reproductive cells, called gametes, that carry only half a set. Two halves make one complete set.

Why Children Are Not Copies

Each gamete carries a different half - a different mix of instructions for eye colour, hair type and everything else. The halves combine differently every time, so no two children are the same. One child may inherit a nose like the mother’s and another may inherit eyes like the father’s.

Flowers: Pollen and Ovule

In a flower, the pollen grains inside the anther are the male gametes and the ovules deep inside are the female ones. Wind, insects or animals carry pollen to another flower, which is pollination. When the two gametes join, that is fertilisation.

From Zygote to Seed and Fruit

Fertilisation forms a zygote, which becomes the seed, and the tissue of the bloom surrounding that ovule swells into the fruit. When a bird eats the fruit, the seed may be dropped far from the parent plant - which is how a banyan can sprout from a crack in a wall.

Animals: In Water, In Eggs, Inside

In animals the gametes are sperm and egg. Fish and frogs release both into water, where they join and the zygote develops there. In birds and mammals the sperm are deposited inside the female. A bird then lays the egg, which carries enough food for the embryo, while in most mammals the young develops inside the mother’s body.

Scenario:

A village nursery sells banana, sugarcane and ginger plants, and a visitor asks to buy seed for all three. The owner says she has none and never has, and sells pieces of stem and root instead. The visitor is suspicious and says every plant must come from a seed. The owner shows him a tray of money plant cuttings rooting in water, a basket of sprouted potatoes with shoots coming from the eyes. And a bed of ginger pieces already in leaf. She also points out that her mango and tomato stock does come from seed, and that she keeps the two kinds of stock in separate sheds for a reason.

Analysis:

The owner is right, and the separate sheds are the clue. The banana, sugarcane and ginger are grown by vegetative propagation. That is a form of asexual reproduction, in which a whole new plant develops from a part of the old one. The part used can be a stem, a root or the eye of a tuber. There is a single parent, so the new plants carry instructions that are exact copies, and every plant in that shed is effectively the same plant repeated. The mango and tomato come from seed, which forms after pollen reaches an ovule and the two gametes join at fertilisation. That involves two parents, each contributing half a set of instructions, so those seedlings vary among themselves. The nursery is therefore selling uniformity in one shed and variety in the other, which is exactly why they are kept apart.

Activity:

Visit a nursery or a kitchen garden and list which plants there are grown from seed and which from a cutting, root or tuber.

Title:

Try it at home: three cuttings and a calendar

Safety:

Cut nothing yourself without an adult, and do not eat any part of a sprouted potato, since sprouts are not safe to eat.

What You Notice:

All three grow into whole plants although no seed was involved, because a leaf, stem or root can carry a complete set of instructions on its own. That is vegetative propagation, and it is why the new plants are exact copies of the ones they came from.

Bamboo and sugarcane are usually grown from pieces of stem rather than from seed, which is why most people have never seen the seed of either.

A planaria flatworm can regrow a whole body from a fragment of itself, and scientists study it to understand how regrowth works in animals generally.

Even yeast, which is a single-celled fungus, has two mating types that behave like the two parents of sexual reproduction.

One parent copies, two parents mix — That is the whole difference. Asexual gives exact copies because there is nothing to mix; sexual gives a fresh combination every time.

Half plus half makes one — Each gamete carries half a set of instructions. Two halves make one complete set, which is why the amount never doubles.

A Balance That Can Be Pushed

Life on Earth rests on a balance between living and non-living systems, and that balance is not guaranteed. A little less oxygen in the air, a little less ozone above it, a slightly higher average temperature - any of these could put living things at risk. None of those numbers has to move far. What makes the situation urgent is that human activity is pushing all three at once, and the four Earth systems are connected, so each push arrives in more than one place.

The Triple Planetary Crisis

Three problems are large enough to be named together: climate change, biodiversity loss and pollution. Taken as one bundle they are called the triple planetary crisis, and the reason for bundling them is that each one makes the other two worse.

Where the Extra Carbon Comes From

Burning coal and oil releases greenhouse gases, mainly carbon dioxide and methane. These gases trap heat in the atmosphere, exactly as the carbon dioxide blanket does on Venus. The result is a rising average temperature, which is called global warming.

Why Earth Cannot Absorb It Fast Enough

Earth already handles carbon dioxide. Trees, plants and even the tiny plankton of the oceans absorb it as they grow. The problem is the rate: the carbon in coal and oil lay underground for millions of years, and releasing it in a few generations is faster than the absorbing can keep up with.

What a Small Rise in Temperature Does

Even a small increase in the average does a great deal. Ice caps melt, so sea levels rise and low coastal cities face flooding. Weather turns more extreme. Plants and animals that cannot cope with the new conditions disappear. None of that needs a large number to happen.

Climate Change, Defined

Shifts of this kind are together called climate change: lasting ones, in how warm a place is, how much rain it gets and what its weather does. The word change matters: it is not one hot year but a lasting move in what counts as normal for a place.

Losing Biodiversity

When natural habitats are destroyed, the plants and animals living in them may disappear. Every kind of living thing has a part to play, so losing even a handful of them leaves the natural world less able to carry life at all. That loss of variety is called biodiversity loss.

One Missing Link in a Food Chain

Follow it through. If the grasses in an area vanish, the animals that eat them - deer and grasshoppers - struggle to survive. Without those herbivores, predators such as tigers and foxes lose their food too. One missing link reaches both upwards and downwards.

Air Pollution

Factories, vehicles and burning fuel put harmful substances into the air. They cause breathing problems in people, damage crops, and produce smog and acid rain. The same air that moderates the planet’s temperature carries the pollution to everything that breathes.

Water and Soil Pollution

Factory, farm and plastic waste harm life in rivers and seas and make water unsafe to drink. Too much fertiliser and careless waste disposal spoil the soil, reduce crop yields, and pass harmful substances along the food chain. Better waste management and more careful farming are the answers.

The Montreal Protocol

Countries have acted together before, and once it worked well. The Montreal Protocol of 1987 cut the use of chemicals called chlorofluorocarbons, or CFCs, which were damaging the ozone layer. The layer has been slowly recovering since.

Earth Summit, Kyoto, Paris

The Earth Summit of 1992 began international work on climate change and biodiversity. The Kyoto Protocol, which came into force in 2005, and the Paris Agreement of 2015 both committed countries to cutting greenhouse gas emissions.

Where the World Stands

The Paris Agreement set a goal of holding global warming below 1.5 degrees Celsius. By 2025, though, the pace of change had not matched what that figure needs. That is worth stating plainly: agreements have been signed, and the measured result so far falls short of what was promised.

What Actually Helps

Since the four Earth systems are connected, damage to one reaches the others, and so does repair. Cutting greenhouse gases means using renewable energy such as solar and wind, using energy more efficiently, and travelling in less damaging ways. Protecting variety matters too, because a diverse ecosystem is a steadier one.

Everyone Can Do Something

Not all of this needs a treaty. Reusing, repairing and recycling clothes and plastic cut both waste and pollution. Saving energy and water adds up across many households. Learning more, telling other people and encouraging them counts as well, and local communities managing their own resources carefully makes a measurable difference.

Scenario:

A town council is told that its new solar panels and its new tree planting are both climate measures. And that its new waste treatment plant is something else entirely. A member objects that all three were approved in the same budget as environmental work and should therefore be reported together. Another says the three cannot be compared, because one produces electricity, one takes in carbon dioxide and one cleans water. The chair asks for a note explaining which of the three crises each measure addresses, and whether any of them helps with more than one.

Analysis:

All three belong to the bundle, and two of them count twice. The solar panels address climate change directly: sunlight is renewable and burning nothing releases no carbon dioxide, so the measure cuts greenhouse gases at source. The tree planting addresses climate change as well, because growing trees absorb carbon dioxide. And it addresses biodiversity loss too, since the trees are habitat for other living things. The waste treatment plant addresses pollution, keeping factory, farm and plastic waste out of rivers and soil. And that also protects biodiversity, because polluted water harms the life in it. So the objecting member is right that they belong in one report, and the second member is right that they work differently. That is exactly why the three crises are named as one: each one makes the other two worse, and each repair helps more than one of them.

Activity:

List three environmental measures in your own town and write beside each which of the three crises it addresses.

Title:

Try it at home: measure what your house throws away

Safety:

Wear gloves, keep food waste out of both containers, and wash your hands after handling anything from either.

What You Notice:

In most households a large share of the total weight turns out to be reusable or recyclable, which is waste and pollution that a single household can cut without waiting for any agreement. Multiply your figure by the number of houses in your street to see what the same habit would be worth locally.

The tiny plankton drifting in the oceans absorb carbon dioxide as they grow, just as trees on land do, which makes the sea part of the planet’s carbon handling.

The Montreal Protocol is often described as the most successful environmental agreement so far, because the damage it set out to stop is genuinely being reversed.

Acid rain forms when polluting gases from factories and vehicles dissolve in rainwater, and it can damage crops and buildings far from where the gases were released.

Climate, variety, pollution — Three names for the three parts: a changing climate, a shrinking variety of life, and pollution. Each one makes the other two worse.

Montreal mended, Paris is pending — The 1987 Montreal Protocol cut CFCs and the ozone layer is recovering. The 2015 Paris Agreement set a 1.5 degree goal and the pace of change has not matched it.