Coaching Centre
Global systems review
A summary of the whole Global Systems chapter, key words, and a mixed test covering Earth's spheres, ocean currents, ENSO and the IOD, cyclones and volcanoes, the phosphorus and oxygen cycles, the energy budget and greenhouse effect, the climate record, impacts and sea level rise, and responses to global change.
Use this page to check the whole chapter. Read the summary, make sure you can explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 7A Earth's spheres | Atmosphere, hydrosphere, lithosphere and biosphere exchange matter and energy. Atmosphere layers: troposphere (weather, temperature falls with height), stratosphere (ozone layer, warms with height), mesosphere, thermosphere (aurora). Air pressure halves about every 5.5 km. Photosynthesis made the oxygen atmosphere over billions of years. |
| 7B Ocean currents | Surface currents are driven by winds and turned by the Coriolis effect into gyres; the East Australian Current carries warm water south, the Leeuwin Current runs south down WA. The thermohaline conveyor is driven by density: cold, salty water sinks near Greenland and Antarctica. Upwelling brings nutrients up and feeds fisheries. AMOC very likely to weaken this century. |
| 7C Oceans and rainfall | Walker circulation: trade winds pile warm water in the western Pacific. El Niño: weak trades, warm water moves east, drier eastern Australia (SOI below −7). La Niña: strong trades, wetter (SOI above +7). Positive IOD dries southern Australia; negative IOD wets it. The SAM affects winter rain in the south. |
| 7D Natural events | Tropical cyclones need sea surface above about 26.5 °C, at least 5° from the equator, and low wind shear; categories 1–5 by gust speed; storm surge is often the deadliest part. Volcanic eruptions affect all four spheres; sulfate aerosols in the stratosphere cooled Earth by about 0.5 °C after Pinatubo (1991). |
| 7E Phosphorus and oxygen | Phosphorus has no gas phase: it cycles from rocks by weathering to soils, organisms, rivers and ocean sediments, and back only by uplift over millions of years. Mined phosphate rock is finite; recycling from waste is needed. Australian plants such as banksias use cluster roots to release phosphorus. Oxygen cycles through photosynthesis and respiration, ozone, water and rocks. |
| 7F Energy budget | Earth absorbs sunlight and emits infrared. Greenhouse gases (CO₂, CH₄, N₂O, H₂O) absorb and re-emit infrared because their molecules bend and stretch; N₂ and O₂ don't. Extra CO₂ creates an energy imbalance until Earth warms. Feedbacks: water vapour and ice–albedo amplify warming. Doubling CO₂ gives about 3 °C (AR6 best estimate). |
| 7G Climate record | Proxies: ice cores (trapped air and isotopes), tree rings, corals, pollen and sediments. Over 800 000 years CO₂ stayed between about 180 and 300 ppm; it is now about 425 ppm. Instruments show about 1.1 °C global warming by 2011–2020 and about 1.5 °C in Australia since 1910. Fingerprints (cooling stratosphere, more warming at night) show the cause is greenhouse gases, not the Sun. |
| 7H Impacts and sea level | Sea level rises from thermal expansion and melting glaciers and ice sheets (not floating sea ice); about 20 cm since 1901, now over 4 mm per year. Impacts in Australia: heatwaves, fire weather, coral bleaching, kelp loss, Torres Strait islands, the Bramble Cay melomys. Mitigation reduces the cause; adaptation reduces the harm. |
| 7I Responding | Montreal Protocol (1987) is fixing the ozone layer. UNFCCC (1992), Kyoto (1997), Paris (2015: well below 2 °C, aim for 1.5 °C). Warming depends on total CO₂ emitted, so the carbon budget is small. Australia: 43% below 2005 by 2030, 62–70% by 2035, net zero by 2050. Caring for Country, cutting waste, e-waste recycling and species recovery are also responses. |
Putting it together
The whole chapter is about Earth as one connected system. Energy from the Sun enters the atmosphere (7A), drives winds and currents that carry heat around the globe (7B), and sets up the ocean–atmosphere patterns that decide whether Australia floods or burns (7C). The same energy powers cyclones, while volcanoes show how events in the lithosphere ripple through every other sphere (7D). Matter cycles too: phosphorus slowly, through rocks, and oxygen quickly, through living things (7E). Greenhouse gases control how much of the Sun's energy stays (7F), and the climate record shows that CO₂ and temperature have always moved together and that today's rise is far outside the natural range (7G). Because the spheres are linked, the extra energy shows up everywhere, in rising seas, heatwaves and changing ecosystems (7H). And because the atmosphere is shared, the response has to be shared as well (7I). First Nations knowledge, built over tens of thousands of years of watching seasons, seas and fire, has always treated Country as one connected system in exactly this way.
Key words
adaptation · aerosol · albedo · atmosphere · biosphere · carbon budget · cluster roots · Coriolis effect · cyclone · density · East Australian Current · El Niño · energy budget · enhanced greenhouse effect · feedback · fingerprint · greenhouse gas · gyre · hydrosphere · ice core · Indian Ocean Dipole · infrared · La Niña · lithosphere · mitigation · Montreal Protocol · net zero · ozone layer · Paris Agreement · phosphorus cycle · proxy · salinity · Southern Oscillation Index · storm surge · stratosphere · thermal expansion · thermohaline circulation · trade winds · troposphere · upwelling · Walker circulation · wind shear
Test yourself
A weather balloon rises through the troposphere. As it rises, the air around it gets
The troposphere is heated from the ground, and pressure falls with height.
Deep water forms near Antarctica mainly because sea water there becomes
Freezing sea ice leaves salt behind, making the cold water very dense.
During an El Niño, eastern Australia usually has
Weak trade winds let the warm pool drift east.
Tropical cyclones almost never form within 5° of the equator because
The Coriolis effect is zero at the equator.
Unlike the carbon cycle, the phosphorus cycle
Phosphorus moves through rocks, soil, water and organisms, not the air.
Which observation is the best evidence that recent warming is caused by greenhouse gases and not by the Sun?
A brighter Sun would warm every layer; trapped heat warms the bottom and cools the top.
Melting of which ice would NOT noticeably raise sea level?
Floating ice already displaces its own weight of water.
Label the steps in the two feedback loops.
Is each action mitigation (reducing the cause) or adaptation (coping with the effects)?
Put these steps of the enhanced greenhouse effect in order.
Cold, nutrient-rich water rising to the surface is called . The reflectiveness of a surface is its . Evidence of past climate stored in ice, tree rings or corals is called a . Sea level rises partly because water expands when heated, called thermal . The layer of the atmosphere where weather happens is the .
Using examples from at least three of Earth's spheres, explain how burning fossil fuels in Australia can affect a coral reef, and evaluate how effective local and global responses could be in protecting it.
Coal, oil and gas were formed from ancient living things and stored in the lithosphere for millions of years. Burning them releases CO₂ into the atmosphere, where it absorbs and re-emits infrared radiation, so Earth takes in more energy than it gives out. About 90% of that extra energy goes into the hydrosphere, warming the ocean and making marine heatwaves more frequent, especially when El Niño or a long run of calm weather adds extra heat. When water stays more than about 1 °C above the usual summer maximum for weeks, corals in the biosphere expel the algae that feed them and bleach; if the heat lasts, they die. About a quarter of the extra CO₂ also dissolves in the sea and makes it more acidic, so corals find it harder to build their skeletons, and stronger cyclones can smash damaged reefs. Local responses help reefs recover: cutting fertiliser and sediment runoff, controlling crown-of-thorns starfish, breeding heat-tolerant corals, and supporting Traditional Owner sea country rangers. But none of these can stop the water warming. Only global action, cutting emissions to net zero in line with the Paris Agreement, removes the cause, and because Australia's emissions per person are high it has a strong responsibility to act. Even then, some further warming is already locked in, so the best outcome needs both: rapid global emissions cuts to limit the heat, and local care to give reefs the best chance of surviving what can't be avoided.