Atmosphere
Earth wears two envelopes: a fluid one, the ocean, and a gaseous one, the atmosphere. The sun heats both — but not equally, and not evenly — and that difference is what sets the air moving. This topic is the air half of the partnership: how it is heated, how it is layered, what it is made of, how it presses down on you — and the two very different ways humans have changed it.
Graaff-Reinet and Gqeberha sit at almost the same latitude, about 200 km apart, under the same sun. Graaff-Reinet's January afternoons average about 30 °C and its July nights about 5 °C, with frost on clear winter nights. Gqeberha's January afternoons average about 25 °C, its July nights about 9 °C — and frost is almost unknown. Same sunshine. What is protecting Gqeberha?
The sea. Water has an enormous specific heat capacity: it takes a great deal of energy to change its temperature, so it warms slowly and cools slowly. Algoa Bay barely changes temperature between day and night and only by a few degrees between seasons, and the air that blows in off it carries that steadiness ashore. CAPS says it in one line: the SHC of water is what dampens seasonal changes in aquatic and coastal environments. Graaff-Reinet, in the middle of the Karoo, has no such buffer — rock and soil heat fast and lose their heat fast.
There is a second reason, and it is also in this topic. Karoo air is dry. Water vapour is a greenhouse gas, so humid coastal air holds the day's heat in overnight, while a clear, dry Karoo sky lets it radiate straight out to space. (Graaff-Reinet also sits about 750 m higher, and air cools with height — a third piece of the same atmosphere story.)
Sea, water vapour, altitude: by the end of this page you will be able to explain all three.
Two Envelopes, One Engine
The sun heats the surface; the surface heats the air from below; heated air moves. The ocean and the atmosphere are two fluids driving each other — one system drives the other.
The chain. The atmosphere is the thin layer of gases and suspended particles that envelopes Earth and is held in place by gravity. Sunlight passes through most of it and is absorbed by the land and sea. The surface then hands heat to the air above it — by radiation, conduction and the evaporation of water — which sets the air moving by convection. Moving air is wind. Wind drags the sea surface into currents. And both winds and currents transport heat, from the hot tropics towards the cold poles.
Why "one system". The atmosphere and ocean are constantly moving, driven by density changes in the air or water and by gravity, and each keeps modifying the other. Winds push the ocean; the ocean's heat and water vapour power the winds and storms. Neither can be understood on its own — which is why an Oceanography course needs a topic about air.
Where this sits. You met the three ways heat travels in Topic 7, and you saw there that the ocean is heated from above (inefficiently) while the atmosphere is heated from below (efficiently). This topic takes that one step further, into the structure of the atmosphere itself and what humans are doing to it.
The Sun's Uneven Gift
Energy from the sun reaches the surface differently depending on where you are and when. Four things decide how much heat a place actually gets.
↑ two beams carrying exactly the same energy. Only the angle differs.
Oblique rays are weaker
Equal areas receive different amounts of solar radiation depending on the angle of the rays: the more oblique (slanted) the rays, the less radiation each square metre gets. Rays arrive at right angles only between 23½° S and 23½° N — between the Tropics of Capricorn and Cancer. So the Equator receives the most solar radiation and the poles the least.
Seasons come from the tilt
Earth spins on an inclined axis. In December the Southern Hemisphere is tilted towards the sun; in June, away from it. On 21 December everywhere south of 66½° S (the Antarctic Circle) has 24 hours of daylight — so the radiation reaching the South Pole swings enormously through the year.
Light surfaces reflect
Radiation striking light surfaces — white clouds, white polar ice — is largely reflected, so less heat gets through to warm the surface. Dark surfaces such as open ocean absorb most of what lands on them. (Remember this one: it comes back in the global warming section.)
More air, less heat
The more air the energy passes through, the more of it is absorbed and scattered on the way. At higher latitudes the rays come in at a low angle and travel through much more atmosphere, so less heat penetrates to the surface.
Careful — the booklet's wording about the seasons hides a famous misconception
Your Two Oceans booklet says the tilt "places the South Pole closer to the sun in December". Read that as tilted towards the sun, not nearer to it. Tilting the pole a few thousand kilometres one way or the other is nothing against the 150 million km between Earth and the sun.
Seasons are caused by the tilt, not by distance. Here is the proof: Earth is actually at its closest to the sun in early January and its farthest in early July — yet the Northern Hemisphere has its winter in January and its summer in July. If distance caused the seasons, both hemispheres would have summer at the same time. What the tilt changes is the angle of the rays (factor ① above) and the length of the day. If an exam asks why December is summer in South Africa, the answer is the tilt of the axis.
Earth's energy budget
The energy budget is the amount of energy gained by Earth in relation to the amount lost. Of every 100 units of sunlight arriving at the top of the atmosphere:
| What happens to it | Share | Made up of |
|---|---|---|
| Reflected straight back to space | 30% | 6% by the atmosphere · 20% by clouds · 4% by Earth's surface |
| Absorbed by the atmosphere | 19% | 16% by the air · 3% by clouds |
| Absorbed by land and oceans | 51% | the energy that powers currents, weather, photosynthesis — everything |
Two sets of numbers — and why they don't contradict each other
The booklet's text rounds the same budget slightly differently: 31% reflected, 17.5% absorbed by the atmosphere, and the remaining 51.5% reaching the surface. Its own NASA diagram (and Topic 7) gives 30 / 19 / 51. Both are estimates of something measured from satellites, and both add up to 100. Learn the pattern, not the decimals: about a third reflected, about a fifth absorbed by the air, about half absorbed by the surface. Quote either set in an exam, as long as your three numbers add up to 100.
And how the surface gets rid of its 51%. The same diagram shows it: about 23% leaves as latent heat in water vapour (evaporation), 7% by conduction and rising air, 15% as radiation absorbed by the atmosphere and 6% radiated straight to space. Nearly half of everything the surface sheds goes up as evaporation — and 71% of the surface is ocean. That is the clearest single reason the ocean drives the atmosphere: the sea is the air's boiler.
The budget is balanced when energy in equals energy out. If more heat were radiated out to space than absorbed, Earth's ocean–atmosphere system would lose heat and cool. If more is absorbed than radiated out, the system warms — and that is what happens when the amount of CO₂ in the atmosphere rises, because it slows the escape of heat. The balance is dynamic: incoming rays, radiation and re-radiation are constantly shifting. Hold that thought until section six.
Same Sunshine, Different Warming
Specific heat capacity (SHC) is the property of a substance that tells you how much heat energy is needed to change the temperature of that substance by one degree Celsius. Put the same energy into four different materials and see what happens.
Land versus sea
Different materials respond to heat differently. Dark objects heat quickly and light ones slowly; solids heat quickly and water slowly — and they cool the same way round. Compare land and sea in the same proportions and you find:
| Land | Sea |
|---|---|
| heats faster | heats more slowly |
| its surface gets hotter for the same sunshine | stays cooler, but stores the heat deeper |
| cools down faster | cools more slowly — retains heat for longer |
| releases more heat into the air above it as it cools, at night and in winter | releases its heat gradually |
One booklet line to read carefully — and one to be proud of
The booklet's second statement is "Land absorbs more heat than the sea." As written, that is the wrong way round. Per square metre the sea absorbs more of the sunlight that lands on it (water is dark and reflects little), and it stores far more, because waves and currents mix the heat metres down, while on land it stays in the top few centimetres. What the booklet means is that land's temperature rises more — its surface gets hotter. That is why the table above says it that way. In an exam, write "land heats up faster and reaches a higher temperature" and you cannot be marked wrong either way.
The proud one: "water has four times more SHC than air." That is exactly right — per kilogram (4 186 J against 1 005 J). The lab above shows why that is only half the story: per cubic metre the gap is about 3 500 times, because air is so light. Work it through and you get one of the most important facts in climate science: the top 2.5 m of the ocean holds as much heat as the entire atmosphere above it.
From heat to wind
Because land releases more heat into the air than the sea does, the air above warm land is heated from below — by conduction, where it touches the ground. The heated air expands, becomes less dense and rises. Cooler, denser air moves in along the surface to replace it, is heated in turn, and rises. That loop is a convection current, and the horizontal part of it, along the ground, is a surface wind. Gqeberha's afternoon sea breeze from the Topic 7 hook is exactly this, on a small scale.
Scale it up and the same process redistributes heat around the whole globe: heat is transferred from one part of the atmosphere to another, and both winds and currents transport heat from the tropics, which receive more than they radiate away, towards the poles, which radiate away more than they receive. The Agulhas Current flowing south past our east coast is the ocean's half of that delivery service.
The Four Layers
The atmosphere has four main layers with thin transition bands called pauses between them. Each layer is defined by what its temperature does as you climb — follow the red line on the right. Tap each layer.
Three things your booklet and study deck say that need a second look
① "The thermosphere's temperature increases, being closer to the Sun." The temperature really does rise — but not because of distance. Being 100 km nearer a sun that is 150 million km away makes no measurable difference. The thermosphere heats up because its few, scattered molecules absorb the sun's most energetic radiation — X-rays and extreme ultraviolet — which never reaches the layers below. The same absorption idea explains the stratosphere (ozone absorbing UV). In an exam, give the absorption reason.
② "Thermosphere … it is cold" (examinable definition). Both halves are true in different senses. Its molecules are moving very fast, so its temperature is high — hundreds of degrees. But there are so few of them that almost no heat would reach you: you would feel cold, and an ascending balloon would burst long before it got there because the pressure is below 1 mb. This is the heat-versus-temperature difference from Topic 7, in the sky. Learn the definition as written, and add "although its temperature is high" if you have the space.
③ "The troposphere contains 90% of all the gas." Quote 90% — it is the booklet's figure. Most atmospheric scientists put it at about 75–80% of the atmosphere's mass, with almost all of its water vapour. The difference comes from where you put the top of the layer, which varies from about 8 km over the poles to about 18 km over the equator; the "15 km" in the booklet is a middle value.
Your turn — draw it (CAPS: "Illustrate using diagrams")
CAPS asks you to illustrate the layers, and the booklet's own question 3 asks you to "illustrate the atmosphere's layers, giving details of their extent and associated temperatures". Looking at the diagram above is not the same as being able to draw it. Close this page and, on blank paper:
① Draw an altitude axis from 0 to 100 km and a temperature axis from −100 °C to +20 °C. ② Plot the profile: +16 °C at the surface, −60 °C at 15 km, back up to 0 °C at 50 km, down to −100 °C at about 90 km, then rising. ③ Draw the three pauses as dashed lines and name them. ④ Name the four layers with their heights. ⑤ Mark the ozone layer, where weather and clouds happen, and the jet streams at the tropopause. Then check it against the diagram. The practical sheet's Investigation 3 turns this into a marked graph from a real data table.
What Air Is — and How It Weighs on You
Air is a mix of gases, water droplets and very small particles. The gases fall into two groups: permanent gases, found in constant percentages of the atmosphere's total volume, and variable gases, which change with time and place.
| Gas | % of dry air | Group | Why it matters |
|---|---|---|---|
| Nitrogen (N₂) | 78.08 | permanent | the bulk of the air; fairly unreactive |
| Oxygen (O₂) | 20.95 | permanent | respiration (Topic 21) — and the raw material of ozone |
| Argon (Ar) | 0.93 | permanent | an inert noble gas; does nothing, but there is a lot of it |
| Carbon dioxide (CO₂) | ≈ 0.043 | variable | tiny share, huge effect: photosynthesis and the greenhouse effect. About 427 parts per million in 2025, and rising |
| Neon, helium, hydrogen, xenon | traces | permanent | together far less than 0.01% |
| Methane (CH₄), nitrous oxide (N₂O), ozone (O₃) | traces | variable | all three are greenhouse gases; ozone also screens UV |
| Water vapour (H₂O) | 0–4 (in real air) | variable | clouds, rain, humidity, and the most abundant greenhouse gas |
"The most common are nitrogen, oxygen, carbon dioxide and water vapour" — CAPS, almost right
That is the CAPS wording, and you can use it. But look at the table: argon outnumbers carbon dioxide more than twenty to one. Argon is the third most common gas in dry air. CAPS is almost certainly listing the most important gases — the ones that drive life and climate — rather than ranking them by amount. If a question asks you to rank the gases by percentage, put argon third.
Air density
Air density is the mass per unit volume of air. Much of the weather depends on it, because denser air sinks and less dense air rises. Three variables change it: temperature, humidity (the amount of water vapour per unit volume) and altitude.
Density increases with…
- a decrease in humidity — drier air
- a drop in temperature — colder air
- a drop in altitude — lower down
Density decreases with…
- an increase in humidity — moister air
- an increase in temperature — warmer air
- an increase in altitude — higher up
Why moist air is lighter — and a typo to fix in your booklet and study deck
Dry, cold air is denser than warm, moist air. The cold part is easy: warm air expands, so the same mass takes up more room. The moist part surprises people — surely adding water makes air heavier? No. A given volume of gas at the same temperature and pressure always holds the same number of molecules. Adding water vapour does not add molecules; it replaces nitrogen and oxygen molecules with water molecules, which are lighter.
📌 The numbers. Water vapour (H₂O) has a molecular mass of 18.02 g/mol, oxygen (O₂) 32.00 g/mol — and nitrogen (N₂) 28.01 g/mol. Your booklet and study deck both print nitrogen as "20.01 g/mol"; that is a typo for 28.01, and the booklet's own next paragraph (a "difference of 10 g/mol") only works with 28. Use 28.01.
Air pressure
Above every square metre of Earth's surface sits a column of air reaching to the top of the atmosphere, pulled down by gravity. Its weight is air pressure: the pressure exerted by the atmosphere on Earth's surface due to the gravitational attraction of the column of air above that point. The average at sea level is 1 013 millibars (mb), measured with a barometer. Weather charts show pressure with isobars — lines joining places of equal pressure.
Low-pressure zone
Air of less than average density, so the pressure is below average and the air tends to rise. Rising air expands and cools, its water vapour condenses — and you get clouds, wind and rain.
High-pressure zone
Air of greater than average density, so the pressure is above average and the air tends to descend. Sinking air is compressed and warms, so clouds evaporate — clear, dry, settled weather.
Read a weather chart
A simplified synoptic chart of the kind the South African Weather Service publishes every day — the booklet's Figure 26.8 is a real one. Isobars are every 4 mb. Tap the four labelled features.
The Air Over Algoa Bay
Local connection — the Windy City, the berg wind, and a station that measures the whole hemisphere
Gqeberha is called the Windy City for a reason. It sits in the path of the winds circling the two high-pressure systems on the chart above, and of the cold fronts that sweep past south of the Cape every few days in winter. On a summer afternoon, land–sea heating adds the sea breeze on top. Every one of those winds is a density difference trying to even itself out.
The berg wind is the strangest of them. A few times each winter, the day before a cold front arrives, the wind swings round to blow off the land — and Gqeberha can have a hot, bone-dry day in the middle of July, sometimes into the 30s °C. The air has come down from the interior plateau, more than a kilometre higher. As it sinks to sea level it moves into higher pressure, is compressed, and warms — the same reason a bicycle pump gets warm. It arrives hot and very dry, which is why berg-wind days are fire-warning days along the Eastern Cape coast. Air density, pressure and altitude, all in one wind.
And at Cape Point, one of the World Meteorological Organization's Global Atmosphere Watch stations samples air that has blown in across thousands of kilometres of Southern Ocean, so it measures the background air of the Southern Hemisphere rather than local pollution. It has recorded CO₂ since 1993 — about 356 ppm at the start — and its monthly background reading crossed 400 ppm in early 2016. South Africa's own instruments are part of the evidence in section eight.
The Greenhouse Effect — Natural, Then Enhanced
Earth's climate changes naturally, and always has. But recent human activities — above all burning fossil fuels — have caused an increase in the rate at which climate regions have shifted and changed.
↑ more greenhouse gas → more of step ③ → less of step ④ → the surface warms until the budget balances again.
Greenhouse gases let incoming short-wave radiation through, but absorb outgoing long-wave radiation — and send part of it back down.
Sunlight arrives mostly as short-wave radiation (visible light), which passes easily through the air and warms the surface. The warm surface then gives off energy as long-wave radiation (infrared) — the warmth you feel from a road after sunset. Greenhouse gases absorb long-wave radiation and re-emit it in every direction, including back down. The result is warmer air covering Earth's surface: the greenhouse effect.
The natural part is essential. Without any greenhouse gases, Earth's average surface temperature would be about −18 °C instead of about 15 °C — a frozen planet. The problem is the enhanced greenhouse effect: humans are adding greenhouse gases faster than the ocean and plants can take them back out, so more heat is held in, and the budget from section two tips towards warming.
| Gas | Main human source | Note |
|---|---|---|
| Carbon dioxide (CO₂) | burning coal, oil and gas; deforestation; cement | the biggest driver of the recent change, because there is so much more of it than of the others |
| Methane (CH₄) | livestock, rice paddies, landfill, gas leaks | much stronger per molecule than CO₂, but shorter-lived |
| Nitrous oxide (N₂O) | fertilisers, some industry | long-lived and potent |
| Water vapour (H₂O) | not directly — it follows temperature | the most abundant greenhouse gas; warmer air holds more, which amplifies warming |
| Ozone (O₃) | low-level ozone from traffic smog | a greenhouse gas near the ground; a UV shield in the stratosphere |
| CFCs, HFCs, PFCs, SF₆ | refrigeration, aerosols, industry | made only by humans; tiny amounts, extremely strong per molecule |
"The CO₂ layer" — a phrase to understand, not to picture literally
CAPS and the booklet both talk about "an increase in the CO₂ layer". There is no separate layer of CO₂ sitting in the sky like a lid. CO₂ is mixed evenly through the whole atmosphere — that is why the diagram above scatters its molecules from the ground to the top. "Layer" is a way of saying "the amount of CO₂ in the air". Use the CAPS phrase if you like, but if you draw it, draw the gas spread throughout, not as a band.
Where the carbon goes
CO₂ is stored in four places: the ocean, the atmosphere, the terrestrial system (plants and soil) and the geology of Earth's crust (limestone, coal, oil and gas). The ocean has always held the most and the atmosphere the least — but human emissions are shifting carbon out of the crust and the forests and into the air. Photosynthesis takes CO₂ back out, but a growing population needing housing and farmland has cleared vast areas of forest, while the burning of oil, coal and wood has added ever more.
The ocean is paying for this twice. It has absorbed roughly a quarter of all the CO₂ humans have released — which slows the warming, but turns some of that CO₂ into carbonic acid. That is ocean acidification, the process you measured with vinegar and shell in the Topic 18 practical, and it threatens every organism that builds a shell or skeleton from calcium carbonate.
The CO₂ figures — what to learn, and three booklet numbers to update
Learn this: before the Industrial Revolution the air held about 280 ppm (parts per million) of CO₂. Measured at Mauna Loa, Hawaii, it was 317 ppm in 1960, 370 ppm in 2000, 401 ppm in 2015 and 427 ppm in 2025 — rising by about 2.6 ppm a year over the last decade, faster than ever.
📌 The booklet's figures are older and need care. ① It gives 1850 as "between 170 and 280 ppm". The 280 is right; 170–180 ppm is the level during the coldest part of the ice ages, not 1850. ② It gives "360 ppm by 2000" — Mauna Loa measured 370 ppm in 2000 (360 was 1995). ③ It gives the annual rise as "1.5–2 ppm" — true for the 1980s and 90s, but the rate has since climbed to about 2.5 ppm a year. The booklet's projection of 2–4 °C of warming by 2100 depends on what humans do next; the lower end needs emissions to fall fast.
The agreements
In 1997, at a United Nations meeting in Kyoto, Japan, industrialised countries agreed to cut their greenhouse gas emissions by an average of about 5.2% below 1990 levels. The gases covered were CO₂, methane, nitrous oxide and sulphur hexafluoride (SF₆), plus the HFCs and PFCs — chemicals invented to replace the ozone-destroying CFCs, which turned out to be powerful greenhouse gases themselves. In December 2015 the Paris Agreement committed its signatories to keep warming well below 2 °C above pre-industrial levels and to pursue efforts to limit it to 1.5 °C.
Four statements in the booklet that are not correct — especially the one about South Africa
① "South Africa has never signed such a climate change / emission reduction agreement." It has signed both. South Africa joined the Kyoto Protocol on 31 July 2002 and ratified the Paris Agreement on 1 November 2016, and it hosted the UN climate conference (COP17) in Durban in 2011. Under Kyoto, developing countries such as South Africa had no binding cut, which may be what the booklet was reaching for. What is true is the second half of the sentence: South Africa still produces most of its electricity from coal, which makes it one of the world's most carbon-intensive economies per person.
② HFCs and PFCs "have destroyed Ozone in the Stratosphere." They have not. Ozone is destroyed by chlorine (and bromine), and HFCs and PFCs contain no chlorine — that is the whole reason they were chosen to replace CFCs. The booklet's own definitions say so. Their problem is the other one on this page: they are strong greenhouse gases, which is why Kyoto covered them, and why a 2016 addition to the Montreal Protocol (the Kigali Amendment) now phases HFCs down. Your study deck repeats this error in its ozone answer.
③ "If these agreements had been adhered to, the level of global emissions would have been reduced by two thirds." Kyoto asked a group of industrialised countries for a cut of about 5% — it could never have removed two-thirds of global emissions. Leave this one out of your answers.
④ The United States and Paris. The booklet was written mid-story. The USA withdrew from the Paris Agreement in 2020, rejoined in 2021, and withdrew again in a process announced in January 2025 that took effect on 27 January 2026. Climate agreements are made and unmade by governments; the physics in section two does not change with them.
The Ozone Hole — a Different Problem, and a Success
The ozone layer in the stratosphere is a screen that protects living things from the sun's harmful ultraviolet (UV) rays. During the last century it was substantially depleted — and then humans did something about it.
CFCs drift up
Chlorofluorocarbons (CFCs) — once used in fridges, air conditioners and spray cans — are stable at ground level. That stability is the problem: nothing breaks them down, so over years they drift up into the stratosphere.
UV sets chlorine free
High up, intense UV light splits them in a photochemical reaction — a reaction caused by light — releasing chlorine radicals. Each chlorine atom breaks up ozone molecules, is released again, and goes on to destroy tens of thousands more.
More UV at the surface
Less ozone means less screening, so more ultraviolet reaches Earth's surface — causing sunburn, skin cancer and eye damage in people, and harming phytoplankton, the base of the marine food web (Topic 22).
The "ozone hole" over Antarctica is not an actual hole: it is a reduction of up to about 70% in the ozone above the continent, which opens each southern spring (September–October) when sunlight returns to the polar stratosphere. In 1987 nations signed the Montreal Protocol on Substances that Deplete the Ozone Layer, phasing out CFCs. It worked. The ozone layer is slowly recovering: the most recent international assessment (2022) expects the Antarctic ozone to return to its 1980 level by about 2066 — close to the booklet's "2070". Kofi Annan, then Secretary-General of the United Nations, called it "the single most successful international environmental agreement to date."
When was the ozone hole discovered? Not quite "the 1970s"
The booklet and study deck both say the ozone hole was discovered "in the 1970s". What happened in the 1970s was the warning: in 1974 the chemists Mario Molina and Sherwood Rowland showed that CFCs could destroy stratospheric ozone. The hole itself was reported in 1985 by British Antarctic Survey scientists measuring from the ground in Antarctica — and the alarm it caused is what got the Montreal Protocol signed only two years later. Molina, Rowland and Paul Crutzen shared the 1995 Nobel Prize in Chemistry for the work. If you write "1970s", say it was when the danger was predicted.
A note on the booklet's two satellite images (September 2000 and February 2015). The hole is seasonal — it opens in spring and closes by summer — so a September picture will always look worse than a February one. A fair test of recovery compares the same month in different years. That is a Topic 5 idea, and it is worth spotting.
| Ozone depletion | Global warming | |
|---|---|---|
| Caused by | CFCs releasing chlorine | greenhouse gases — mainly CO₂ |
| Where | the stratosphere | mainly the troposphere and the surface |
| Radiation involved | more incoming UV gets through | less outgoing long-wave (infrared) gets out |
| Effect | more UV at the surface — sunburn, cancer, damaged plankton | a warmer planet, rising seas, acidifying oceans |
| The agreement | Montreal Protocol, 1987 — working | Kyoto 1997, Paris 2015 — targets not yet met |
The one link between them: CFCs are greenhouse gases too, so by removing them the Montreal Protocol has also slowed global warming — one of its least-known successes. But the ozone hole did not cause global warming, and fixing it will not stop global warming.
The Evidence for Global Warming
CAPS asks you to describe evidence for global warming. Satellites and decades of measurement on land, at sea and in the ice show the signals of a changing climate:
How to answer an "evidence" question
Evidence is what has been measured or observed — not the cause. "Burning fossil fuels" is a cause; "rising CO₂ in the atmosphere" is the link; "rising sea levels" is evidence of warming. A strong answer names the observation and says how it shows warming: "Sea levels are rising, because warming water expands and melting land ice adds water to the ocean."
South African evidence you can use: Cape Point's CO₂ record (section six); the 2015–2018 drought that brought Cape Town close to "Day Zero", which scientists estimated climate change had made about three times more likely; and warming, acidifying seas around our coast. The rapid rise in greenhouse gases is changing the climate faster than some living things can adapt — a new, more unpredictable climate puts multiple stresses on all life at once.
In the Lab — the CAPS Investigations
CAPS lists one investigation for this block, in two words: "Greenhouse gases". The practical sheet builds that into a proper experiment, and adds the land-versus-sea measurement, the drawing CAPS asks for, and a real data set.
Four investigations · the first two need only a lamp, two jars and a thermometer
- 🟢 kitchen Land versus sea — heat dry sand and water under the same lamp, then switch it off and let them cool. Two heating curves and two cooling curves show specific heat capacity at work, and why Gqeberha's winters are mild.
- 🟢 kitchen 🟡 thermometers The CAPS investigation: greenhouse gases — two sealed bottles under a lamp, one filled with CO₂ from vinegar and bicarbonate of soda. Measure the difference — and then work out honestly what this model does and does not show.
- 🟢 desk Draw the atmosphere — plot real temperature-against-altitude data, then mark the four layers, the three pauses and the ozone layer, as CAPS asks.
- 🟢 desk Read the evidence — graph 65 years of Mauna Loa CO₂ measurements, calculate the rate of rise decade by decade, and separate evidence from cause.
→ Open the Topic 26 practical sheet — printable, with supplied data for every task.
Key Vocabulary
Tap each card to flip it. These seventeen are the topic's examinable definition list, in the booklet's own words — every one of them.
The thin layer of gases and suspended particles which envelopes Earth and which is kept in place by gravity.
The amount of energy gained by Earth in relation to the amount of energy that is lost. Balanced, the climate is steady; tipped towards gain, it warms.
The property of a material that prescribes how much heat energy is required to change the temperature of that material by one degree Celsius. Water's is very high: 4 186 J per kg per °C.
The first 15 km above Earth, containing 90% of all the gas found in the atmosphere. All weather happens here, and temperature falls with height.
The layer above the troposphere that extends to an altitude of 50 km and contains the important ozone. (The booklet calls ozone an "element"; strictly it is a molecule of the element oxygen.)
The layer above the stratosphere with very low levels of gas, air pressure and solar radiation. Temperature plummets to about −100 °C.
The layer higher than 90 km and into space; it is cold and air pressure is below 1 mb. "Cold" in the sense that you would feel no warmth — its measured temperature is actually very high.
An unstable form of oxygen (O₃) found up to an altitude of 40 km within the stratosphere that absorbs ultraviolet light out of the sun's light rays.
A group of atoms bonded together; the smallest unit of a compound that can take part in a chemical reaction. O₂, O₃, CO₂ and H₂O are all molecules.
The mass per unit volume of air in Earth's atmosphere. Increased by cold, dry air and low altitude; decreased by warm, moist air and height.
The pressure exerted by the atmosphere on Earth's surface due to the gravitational attraction of a column of air above a specific point; the volume of air pressing down on the surface of Earth.
A unit to measure atmospheric pressure, measured by a barometer. Average sea-level pressure is 1 013 mb.
A line that joins the localities of constant (equal) air pressure on a weather chart. Closely spaced isobars mean strong winds.
Relating to or caused by the chemical effects of light on a substance — like UV splitting a CFC molecule high in the stratosphere.
Chlorofluorocarbons: chemical compounds that are stable at ground level but at higher altitude undergo a photochemical reaction which sets free chlorine radicals, which break up ozone.
Hydrofluorocarbons: industrial chemicals developed to replace CFC ozone-depleting chemicals and used mainly for refrigeration; they contain carbon, fluorine and hydrogen. No chlorine — but strong greenhouse gases.
Perfluorocarbons: a group of industrial chemicals made of carbon and fluorine only, developed to replace CFC ozone-depleting chemicals. Also strong, very long-lived greenhouse gases.
General terms to know
Ambient: what is surrounding or present. · Emissions: the release of gas or other substances into the atmosphere. · Greenhouse gases: gases which absorb radiation, such as water vapour, methane, CFCs and carbon dioxide. · Insulate: protect from loss or unwanted gain of heat. · Jet stream: a narrow belt of strong upper-atmosphere winds, found about 7.5–14 km above Earth's surface and 2–4 km deep. · Nullified: made invalid or ineffective. · Oblique: at an angle. · Plummets: drops sharply.
Quick Check
Question 1
Well done!
That is the air half of the ocean–atmosphere partnership. Next: what humans are doing to the life in the sea.