Ausgeology. Senior secondary lessons

SACE Stage 2 Earth and Environmental Science · Topic 4: Climate change

Climate drivers.

Long before people, Earth’s climate swung between extremes: ice that may have reached the equator, and a hot spike that likely warmed the world by 5 to 8 °C. This lesson looks at what drives those changes: the gases in the air, the Sun and Earth’s orbit, moving plates and volcanoes, and the oceans, which store heat and carry it around the world.

Slide sideways to see the whole picture.

Illustration
The drivers of climate in this lesson, in one slice of the Earth system. Not to scale: the Sun, the orbit and the air are drawn far closer and smaller than they are.
  • 1The Sun and Earth’s orbit (screen 5)
  • 2Greenhouse gases in the air (screens 2 to 4)
  • 3Ice and snow reflect sunlight (screen 3)
  • 4Volcanoes and moving plates (screen 6)
  • 5The ocean stores heat (screen 7)
  • 6Ocean currents carry heat (screen 8)

Past climates in Australia’s rocks

Pilbara, Western Australia

The oldest fossils on Earth are stromatolites from Western Australia, about 3.5 billion years old: layers built up by communities of microbes, from a time when the air held almost no oxygen.

Geoscience Australia; NASA

Flinders Ranges, South Australia

Rocks left by glaciers 717 to 635 million years ago, when ice may have covered the planet from the poles to the equator: Snowball Earth.

University of Sydney; UNESCO

Bass Strait

About 20,500 years ago the sea was 125 to 130 m lower than today, and Tasmania, the mainland and New Guinea were one land mass. The sea rose and cut Tasmania off about 12,000 years ago.

Yokoyama and others (2018); National Museum of Australia

Hot and cold

Billions of years

What we are learning

The natural processes that have changed Earth’s climate over geological time: in the atmosphere, outside it and within the Earth, and in the oceans, which absorb solar radiation and carry heat around the world.

I can

  • 1describe how Earth’s atmosphere has changed, and why.
  • 2explain how solar energy is absorbed, re-emitted and reflected, including the albedo effect.
  • 3explain the greenhouse effect, and how a gas’s lifetime and its absorption of infrared set its warming potential.
  • 4explain how astronomical cycles and sunspots change the energy Earth receives.
  • 5explain how the plate-tectonic supercycle has changed Earth’s climate.
  • 6explain how water’s large specific heat capacity affects ocean temperatures.
  • 7explain the difference between surface and deep-water currents, and what drives each.
  • 8connect events in Earth’s climate history to the drivers behind them.

SACE Stage 2 Earth and Environmental Science, Topic 4: Climate change. This lesson covers the natural drivers of climate, the topic’s first five Science Understanding statements. The evidence for climate change, the effect of human activities, the effects of climate change on the Earth system and climate models are for the Climate evidence lesson, coming next.

How this lesson works: peer instruction

  1. Answer on your own. Each concept question is about an idea that many people get wrong. Think, then choose.
  2. Convince a partner. Find someone who chose differently if you can, and take turns to explain your reasoning.
  3. Answer again. Keep your answer or change it.
  4. Read the explanation, then go on with the screen.

Screens 2 to 8 have one or two concept questions each, after the models and data that help you answer them. Working alone? Each question can show you two students’ arguments to weigh up instead. Screen 9 brings the drivers together, and screen 10 has eight questions.

Your answers and notes are saved in this browser, so you can stop and come back.

My notebook

Printable activity

Heat capacity practical

Two pages: measure the specific heat capacity of water and of sand or another material, graph the results, and use them to explain why the sea warms and cools more slowly than the land. It goes with screen 7.

Activity sheet (PDF) Editable (Word)

2In the atmosphere

The air through time.

How did Earth get the air it has now?

Earth’s air has changed completely since the planet formed. Gases from volcanoes made a first atmosphere with almost no oxygen. Living things then added oxygen, and with it came an ozone layer. Step through the changes, and look for the evidence each one left in the rocks.

The evidence in Western Australia

Pilbara

Early life

Rocks 3.48 billion years old in the Dresser Formation hold signs of life in ancient hot springs on land (UNSW). The 3.43 billion-year-old Strelley Pool Chert holds a stromatolite reef (Allwood and others, 2007; NASA). Both were built by microbes; these sources do not say which kinds.

UNSW (2017); Allwood and others (2007); NASA Earth Observatory

Hamelin Pool, Shark Bay

Living stromatolites

The first modern, living stromatolites to be recognised. Similar structures dominated life in the sea for more than 3,000 million years (UNESCO). Today’s are built by cyanobacteria, which give off oxygen as they photosynthesise (Geoscience Australia).

UNESCO World Heritage List; Geoscience Australia

Banded iron formations

Oxygen meets iron

Layers of iron oxides and silica laid down on the sea floor about 2.5 billion years ago, as cyanobacteria greatly increased the oxygen in the oceans and the atmosphere, and iron dissolved in the water combined with it.

Australian Museum

Today’s air. Dry air is 78.084% nitrogen, 20.946% oxygen, 0.934% argon and 0.042% carbon dioxide, with other gases in tiny amounts (NOAA). The average amount of carbon dioxide reached 425.62 parts per million in 2025 (NOAA). These figures are for completely dry air, but real air is rarely, if ever, dry: on hot, humid days water vapour can make up nearly 3% of it, and close to 4% in the tropics (NOAA). The next two screens show why the small amounts of carbon dioxide, water vapour and a few other gases matter so much.

Key idea

Earth’s first atmosphere came from outgassing: gases released from inside the Earth, with more carbon dioxide than now and almost no oxygen. Cyanobacteria added oxygen by photosynthesis; it rose in the air about 2.4 billion years ago, in the Great Oxidation Event, and let an ozone layer form. Fossil stromatolites and banded iron formations record the change.

My notebook

3In the atmosphere

The energy budget.

Where does the Sun’s energy go, and what keeps Earth warm?

Sunlight brings energy to Earth. Some is reflected straight back to space. The rest is absorbed by the air, the land and the sea, which give it off again as infrared. The balance between the energy coming in and going out sets Earth’s temperature.

Earth’s energy budget

Global averages, W/m²
Show the numbers as a table

Each number is an average over the whole globe, by day and night, in watts per square metre, from the IPCC (2021). Energy in and out nearly balance, but not quite: at the beginning of the 21st century, about 0.7 W/m² more came in than went out, so Earth was gaining heat.

Reflected, absorbed and given off again. Earth’s energy budget follows the energy in and out. Of the 340 W/m² of sunlight arriving at the top of the atmosphere, 100 is reflected back to space by clouds, the air, ice and the surface. The air absorbs 80 and the land and sea 160. The warm surface then gives off 398 W/m² of infrared, more than the sunlight it absorbs, because it also receives 342 W/m² of infrared from the air. Water evaporating from the surface carries 82 W/m² up into the air as latent heat, and rising warm air carries another 21 as sensible heat. In the end, 239 W/m² of infrared leaves for space.

Albedo. The share of sunlight a surface reflects is its albedo, from 0 for none to 1 for all. For Earth as a whole it is about 0.29: NASA gives 0.294, and Penn State’s course notes 0.31. Clouds do much of the reflecting: without them, about 47 W/m² less sunlight would be reflected (IPCC). The surface matters too.

Light and dark surfaces

Albedo
Show the numbers as a table

Key idea

About 29% of the sunlight reaching Earth is reflected; the rest is absorbed by the air and the surface. The surface gives the energy off again as infrared, and the air sends much of it back down. Ice and snow reflect far more sunlight than open ocean or forest, so when ice melts, the surface absorbs more energy and warms further: a positive feedback.

My notebook

4In the atmosphere

Greenhouse gases.

Which gases keep Earth warm, and why are some far stronger than others?

Nitrogen and oxygen make up 99% of dry air, but they let infrared pass straight through. A few gases present in tiny amounts absorb it. How much each one warms the planet depends on how strongly it absorbs infrared and how long it lasts in the air.

The greenhouse effect. Greenhouse gases such as carbon dioxide make it harder for heat to escape (Bureau of Meteorology). They absorb infrared from the surface and give off infrared of their own in all directions, so some returns to the surface: the 342 W/m² on screen 3. Without this greenhouse effect, Earth’s average surface temperature would be about −18 °C rather than about 15 °C (CSIRO). The Australian Academy of Science puts it this way: Earth’s surface would be about 33 °C cooler without it, so it keeps Earth habitable.

Which gases absorb infrared?

0 of 7 sorted

Why some gases and not others. Molecules with three or more atoms can vibrate in more complex patterns, which is why carbon dioxide absorbs and gives off infrared while nitrogen and oxygen molecules do not (UCAR). For a gas to absorb infrared, its vibration has to change how electric charge is spread through the molecule, and a molecule of two identical atoms cannot do that (Hong Kong Observatory).

Water vapour. Water vapour is one of the most important greenhouse gases, but NASA explains that more water vapour does not cause global warming: it is a consequence of it. Warmer air holds more water vapour, which absorbs more infrared and warms the air further, and scientists estimate this more than doubles the warming carbon dioxide alone would cause (NASA). It is a positive feedback.

Strength and staying power

Global warming potential
Show the numbers as a table

A gas’s global warming potential measures how much energy one tonne of it absorbs over a set time, usually 100 years, compared with one tonne of carbon dioxide (US EPA). Two things set it: how strongly the gas absorbs infrared, and how long it lasts. Methane absorbs far more than carbon dioxide but lasts only about a decade on average; nitrous oxide lasts more than 100 years (US EPA). Carbon dioxide has no single lifetime: more than half of what is emitted is removed within a century, but about 20% stays in the atmosphere for many millennia (IPCC, 2007).

Australia reports its emissions with the slightly different values from the IPCC’s Fifth Assessment Report: 28 for methane and 265 for nitrous oxide (Clean Energy Regulator). The chart uses the Sixth Assessment Report’s.

Key idea

Greenhouse gases absorb infrared given off by Earth and send some of it back down, warming the surface by about 33 °C. Molecules of three or more atoms can do this; nitrogen and oxygen cannot. A gas’s global warming potential depends on how much energy each tonne absorbs and how long it lasts in the air, so a short-lived gas such as methane counts for more over 20 years than over 100.

My notebook

5Outside the atmosphere

From space.

How do changes in Earth’s orbit, and in the Sun itself, change the climate?

The energy Earth receives depends on the Sun and on Earth’s path around it. The shape of the orbit and the tilt and wobble of Earth’s axis change over tens to hundreds of thousands of years, changing where and when sunlight falls. The Sun’s own activity rises and falls every 11 years or so.

Three cycles in Earth’s orbit

About 100,000 years

Eccentricity: the shape of the orbit

The orbit changes from nearly circular to slightly elliptical and back (NASA). Its eccentricity has ranged from about 0.0034 to 0.058 (Stull). Today it is 0.0167, so Earth is 147.1 million km from the Sun at its closest and 152.1 million km at its farthest (NASA).

About 41,000 years

Obliquity: the tilt of the axis

Over the last million years Earth’s tilt, its obliquity, has varied between 22.1° and 24.5°. Today it is 23.4°, about halfway, and slowly decreasing (NASA). The tilt causes the seasons.

About 23,000 years

Precession: the wobble

Earth’s axis wobbles like a spinning top, so the season in which Earth is closest to the Sun changes, over about 23,000 years on average (NASA). This is precession. Today Earth is closest to the Sun in early January (NASA).

Together these Milankovitch cycles change the insolation, the sunlight reaching Earth’s mid-latitudes, by up to 25% (NASA). Milutin Milankovitch chose summer sunlight at 65° north as the most important to model: cooler summers there might let snow last through the summer, so that ice sheets grow (NASA Earth Observatory). In 1976, Hays, Imbrie and Shackleton found his cycles in deep-sea sediment cores covering the last 450,000 years. Ice ages came every 41,000 years between 1 and 3 million years ago, then about 800,000 years ago the cycle lengthened to 100,000 years (NASA).

The Sun’s own cycle. Sunspots come and go in a cycle of about 11 years (Bureau of Meteorology), caused by the reversal of the Sun’s magnetic poles (NOAA). In a strong cycle the Sun is about 0.1% brighter at solar maximum, when there are most sunspots, than at solar minimum: up to about 1 W/m² (NOAA). Between 1645 and 1715 there were few sunspots, a time called the Maunder Minimum (NASA). It came during the Little Ice Age, a cold spell from the 13th to the mid-19th century. Some people have linked the Maunder Minimum’s cooling to the quiet Sun, but NASA says it was more likely influenced by increased volcanic activity and shifts in ocean circulation.

Three centuries of sunspots

Data
Show the numbers as a table

The yearly mean total sunspot number from WDC-SILSO, Royal Observatory of Belgium, Brussels. The yearly record starts in 1700, near the end of the Maunder Minimum.

Key idea

Changes in the shape of Earth’s orbit, the tilt of its axis and its wobble change where and when sunlight falls over tens to hundreds of thousands of years, and set the timing of the ice ages. The Sun’s brightness rises and falls with the 11-year sunspot cycle, by about 0.1% in a strong cycle, and the IPCC finds that natural drivers changed global temperature by only −0.1 to +0.1 °C between 1850–1900 and 2010–2019.

My notebook

6Within the Earth

From within.

How have moving plates and volcanoes changed Earth’s climate?

Plates move only centimetres a year, so their effects on climate build up over millions of years. As continents gather and break apart, they change where land and sea lie, where currents can flow and where ice can grow. Volcanoes and the weathering of rock move carbon dioxide into and out of the air.

The supercontinent cycle. Oceans can close and then open again, in what is called the Wilson cycle (Britannica). Again and again the continents have gathered into one supercontinent and broken apart, roughly every 500 to 700 million years (Curtin University): the supercontinent cycle, or supercycle. Rodinia formed about 1.2 billion years ago and held together until 750 million years ago (Britannica), though Curtin University dates its assembly to 900 million years ago. Pangaea was fully assembled by the Early Permian, some 299 to 273 million years ago, and began to break apart about 200 million years ago. Bringing so much land together led to extensive dry climates in its tropics in the Permian (Britannica).

Mountains. Air cools by about 6.5 °C for each kilometre of height, the lapse rate (NOAA), so as colliding plates raise mountains and plateaus, the climate there gets colder. Raymo and Ruddiman (1992) argued that the uplift of the Tibetan plateau may have cooled the whole planet over the last 40 million years: more weathering of the new rock may have taken carbon dioxide out of the air.

The long-term thermostat. In the slow carbon cycle, carbon moves between the air and the rocks. Carbon dioxide combines with water to form carbonic acid, which falls in rain and dissolves rock. This chemical weathering releases ions that rivers carry to the ocean, where calcium carbonate settles on the sea floor and becomes limestone. Volcanoes return the carbon to the air (NASA Earth Observatory). Put the steps in order.

Close the loop

Put the cycle in order

When the thermostat failed. In the Sturtian glaciation, about 717 to 660 million years ago, ice may have blanketed the planet from the poles to the equator. University of Sydney researchers link its start to historically low volcanic carbon dioxide, aided by the weathering of a large pile of volcanic rocks. A second worldwide glaciation, the Marinoan, ended about 635 million years ago. Both left glacial deposits in the Flinders Ranges, where the rock laid down as the Marinoan ended marks the start of the Ediacaran Period at Enorama Creek: the only such international marker in the Southern Hemisphere (International Commission on Stratigraphy; UNESCO).

Key idea

Over hundreds of millions of years the continents gather into supercontinents and break apart. Their positions decide where ocean currents can flow and ice can grow: when Australia and South America pulled away from Antarctica, ocean gateways opened and the Antarctic Circumpolar Current began to circle it. Volcanoes add carbon dioxide and the weathering of rock removes it, a carbonate–silicate cycle that steadies Earth’s temperature over a few hundred thousand years.

My notebook

7The oceans

Oceans store heat.

Why do the oceans warm and cool so slowly?

Water needs a great deal of energy to warm up. So the oceans can take in huge amounts of the Sun’s energy while their temperature changes only slowly, and they steady the temperature of the coasts beside them.

A material’s specific heat capacity is the energy needed to raise the temperature of 1 kg of it by 1 °C (Your Home). Water’s is 4,186 J/kg °C, about five times that of granite (OpenStax). The same energy, put into the same mass, raises the temperature of a material with a large specific heat capacity far less:

energy = mass × specific heat capacity × temperature rise
E = m × c × ΔT

The ocean as a heat store. The top two metres of the ocean hold about as much heat as the whole column of air above them (NOAA). Of all the extra heat added to the climate system in recent decades, the IPCC finds that ocean warming accounted for 91%.

Where the extra heat has gone

IPCC data
Show the numbers as a table

Around Australia, the average sea surface temperature has warmed by 1.08 °C since 1900 (State of the Climate 2024). The causes of recent warming are for the Climate evidence lesson.

The coast and the inland

The high heat capacity of water keeps its temperature within a relatively narrow range, so coastal areas nearby also have a narrow daily and seasonal range of temperature; areas with similar weather farther from the coast tend to have a much wider range (Florida Atlantic University). Compare two South Australian weather stations about 200 km apart.

Near the coast

Adelaide (West Terrace)

Average maximum 21.9 °C. Average minimum 12.1 °C.

Bureau of Meteorology, station 023000, 1887 to 2026

Inland

Renmark Aero

Average maximum 25.0 °C. Average minimum 9.8 °C.

Bureau of Meteorology, station 024048, 1995 to 2026

Work out the gap between the average maximum and minimum at each station. Which statement fits the data?

The stations’ records cover different years, and other things differ between them too, such as rainfall and cloud. A fair test would compare many stations over the same years.

The same comparison in the Northern Territory

Darwin Airport is near the coast. Tindal, near Katherine, is about 280 km to the south-east.

Near the coast

Darwin Airport

Average maximum 32.1 °C. Average minimum 23.3 °C.

Bureau of Meteorology, station 014015, 1941 to 2026

Inland

Tindal RAAF

Average maximum 34.2 °C. Average minimum 20.6 °C.

Bureau of Meteorology, station 014932, 1985 to 2026

Key idea

Water has a very large specific heat capacity: 4,186 J/kg °C, about five times that of rock or sand, so the same energy warms it far less. The oceans have taken up 91% of the heating in the climate system (IPCC), and they steady the temperatures of the coasts beside them.

My notebook

Printable activity

Heat capacity practical

Measure the specific heat capacity of water and of sand or another material, and use your results to explain why the sea changes temperature more slowly than the land.

Activity sheet (PDF) Editable (Word)

8The oceans

Ocean currents.

What drives the ocean’s currents, and how do they change the weather?

Currents carry heat around the world. Near the surface the winds drive them; in the deep ocean, differences in the water’s temperature and saltiness do. When the winds and currents of the tropical Pacific change, as in El Niño and La Niña, Australia’s rainfall changes too.

Winds drive the surface currents. Large-scale surface currents are driven by global wind systems, which are fuelled by energy from the Sun (NOAA). In the tropics, the trade winds blow towards the equator, where they meet in the doldrums; in the Southern Hemisphere they blow from the south-east. Farther from the equator, the westerlies blow between about 35° and 60°, and polar easterlies blow outwards from the poles (NOAA). Because Earth spins, winds and currents are deflected to the left in the Southern Hemisphere and to the right in the Northern: the Coriolis effect. In the Southern Hemisphere, water in a wind-driven current moves about 90° to the left of the wind (University of Hawaiʻi).

Together, the trade winds and the westerlies turn the surface water of each ocean in a huge loop, a gyre: clockwise in the Northern Hemisphere and anticlockwise in the Southern. There are five major gyres, each with a strong, narrow current on its western side and a weak, broad one on its eastern side (NOAA). Winds drive currents only in the upper 100 m or so of the ocean (NOAA); other sources give 50 to 100 m, or 100 to 200 m. Surface currents involve only about 10% of the world’s ocean water (Webb).

Density drives the deep currents. Deep-ocean currents are driven by differences in the water’s density, which depends on its temperature (thermo) and salinity (haline): the thermohaline circulation (NOAA). In the polar regions, sea water freezes into sea ice and leaves its salt behind, so the water around the ice gets saltier and denser, and sinks (NOAA). The densest water of all, Antarctic Bottom Water, forms in the Weddell Sea (Webb). It is created when sea ice forms in winter close to Antarctica, there and in the Ross Sea, off the Adélie Coast and at Cape Darnley (Australian Antarctic Division). The deep water spreads slowly through the ocean basins: a cubic metre takes about 1,000 years to complete the journey (NOAA).

Science in progress: the IPCC (2021) finds that the Atlantic Meridional Overturning Circulation, the Atlantic part of this circulation, is very likely to weaken over the 21st century, with only low confidence in by how much, and medium confidence that it will not collapse abruptly before 2100.

El Niño and La Niña. In the tropical Pacific, the ocean and the air work together. In neutral years, steady trade winds pile up warm water in the western Pacific, and air rises to Australia’s north and sinks near South America: the Walker Circulation. In El Niño the trade winds weaken and warm water spreads east; in La Niña they strengthen and warm water builds up north of Australia (Bureau of Meteorology).

The Indian Ocean has a similar pattern, the Indian Ocean Dipole: a positive IOD often brings less rain and higher temperatures to parts of Australia in winter and spring, and a negative IOD more rain to parts of southern Australia (Bureau of Meteorology). On 27 October 2026, the Bureau reported a strong El Niño continuing and a positive IOD underway.

Key idea

Surface currents are driven by the wind belts, turned into gyres by the Coriolis effect, and reach only the top hundred metres or so. Deep-water currents are driven by differences in density, from temperature and salinity, as cold, salty water sinks near the poles and spreads slowly through the deep ocean. Changes in the tropical Pacific’s winds and currents, El Niño and La Niña, change rainfall across Australia.

My notebook

9All the drivers

Putting it together.

Which driver was behind each change, and how fast does each one work?

Earth’s climate changes when the energy it absorbs or gives off changes. The drivers work on very different timescales, and often together. Sort each event by the driver behind it. Where two drivers were at work, either counts.

What drove it?

0 of 10 sorted

From months to millions of years

Timescales
Show the numbers as a table

Feedbacks. A driver rarely acts alone. Some changes feed themselves: melting ice exposes darker ocean that absorbs more sunlight (screen 3), and warmer air holds more water vapour, which traps more heat (screen 4). These positive feedbacks make a change bigger. Others work against the change: warmer weather speeds up the weathering that takes carbon dioxide out of the air (screen 6), a negative feedback that slowly steadies the temperature.

Key idea

The Sun and Earth’s orbit change how much sunlight arrives, and where. The air, clouds and ice change how much is reflected and how much infrared escapes. Plates, volcanoes and weathering change the air and the shape of the oceans over millions of years. The oceans store heat and carry it around the world. Feedbacks can make a change bigger or smaller.

My notebook

10Show what you know

Show what you know.

Eight questions, one for each of the I can statements on screen 1. You get one try at each, so think before you tap.

Banded iron formations were laid down on the sea floor about 2.5 billion years ago. What are they evidence of?

If snow and ice spread over more of Earth, what happens to Earth’s albedo and its temperature?

Over 100 years, nitrous oxide has a global warming potential of 273 and carbon dioxide 1. Why?

Which orbit would give the Northern Hemisphere the coolest summers, the conditions Milankovitch linked to growing ice sheets?

How can moving plates change Earth’s climate over millions of years?

The same energy is put into 1 kg of water and 1 kg of granite. What happens?

Which statement about ocean currents is correct?

The Antarctic ice sheet grew quickly about 34 million years ago. Which two drivers have scientists argued over as the cause?

Printable activity

Heat capacity practical

Measure the specific heat capacity of water and another material, and explain why the oceans change temperature slowly.

Activity sheet (PDF) Editable (Word)
For teachers

Curriculum

SACE Board of South Australia, Stage 2 Earth and Environmental Science Subject Outline (accredited for teaching at Stage 2 from 2018, reissued for 2025), Topic 4: Climate change. NT students take the subject as part of the NTCET. The topic outline says:

In this topic, students explore how climate variables have changed over geological time, due to natural processes occurring in the Earth’s atmosphere, outside the atmosphere, and within the Earth. They recognise why significant variation in the Earth’s climate has the potential to produce a major effect on the Earth’s systems and on life on this planet.

This lesson covers the topic’s first five Science Understanding statements, the natural drivers of climate. The other four (anthropogenic activities, the effects of climate change on the Earth system, the evidence from records and proxies, and climate models) are for the Climate evidence lesson.

Natural processes in the Earth’s atmosphere affect climate change over geological time.

  • Discuss the evolution of the Earth’s atmosphere.
  • Explain how the composition of the Earth’s atmosphere changes over time.
  • Discuss the greenhouse effect.
  • Explain how the lifespans of greenhouse gases and their ability to absorb infrared radiation contribute to their warming potentials.
  • Discuss how solar energy is absorbed, re-emitted, and reflected by atmospheric gases and the Earth’s surface, including the albedo effect.

Natural processes outside of the Earth’s atmosphere affect climate change over geological time.

  • Explain how astronomical cycles affect natural climate variability.
  • Explain how variations in solar energy due to sunspot activity can contribute to natural climate change.

Natural processes within the Earth affect climate change over geological time.

  • Explain how the plate-tectonic supercycle has contributed to global climatic changes throughout the Earth’s history.

Oceans absorb large amounts of solar radiation.

  • Explain the effect of water’s large specific heat capacity on changes in ocean temperature.

Changes in oceanic circulation may impact on weather systems.

  • Explain the difference between surface and deep-water ocean currents.
  • Explain the relationship between the world’s wind belts and the world’s surface ocean currents.
  • Explain the relationship between the thermohaline circulation and deep-water ocean currents.

Where the lesson covers them:

  • Natural processes in the atmosphere: the evolution and changing composition of the atmosphere, screen 2 (a five-step model and the evidence in Western Australia’s rocks); the greenhouse effect and the lifespans, infrared absorption and warming potentials of greenhouse gases, screen 4; solar energy absorbed, re-emitted and reflected, and the albedo effect, screen 3 (the IPCC energy budget, surface albedos and a planet model).
  • Natural processes outside the atmosphere: screen 5 (Milankovitch cycles with an orbit model; sunspot numbers since 1700, the Maunder Minimum and the size of the solar cycle’s effect).
  • Natural processes within the Earth: screen 6 (the Wilson and supercontinent cycles, Rodinia and Pangaea, mountains, Australia and South America leaving Antarctica, the carbonate–silicate cycle, and Snowball Earth in the Flinders Ranges).
  • Oceans absorb solar radiation: screen 7 (a heating lab, the IPCC’s share of heat taken up by the ocean, and coastal and inland temperatures in South Australia and the Northern Territory). The printable practical is the outline’s suggested context, investigating the specific heat capacity of water and other substances.
  • Changes in oceanic circulation: screen 8 (wind belts and surface currents, gyres and the Coriolis effect, the thermohaline circulation and deep water, El Niño, La Niña and the Indian Ocean Dipole). Continental distribution and ocean currents, and mountain building and climate, two of the outline’s possible contexts, are on screen 6.

Science as a human endeavour runs through the lesson. Its key concepts in the outline include these, used on the screens shown:

Development of complex scientific models and/or theories often requires a wide range of evidence from many sources and across disciplines.

Screen 5: Milankovitch’s theory, tested in 1976 against deep-sea sediment cores; screen 2: the evolution of the atmosphere pieced together from fossils, banded iron and zircon crystals.

New technologies improve the efficiency of scientific procedures and data collection and analysis. This can reveal new evidence that may modify or replace models, theories, and processes.

Screen 5: satellites measuring the Sun’s output for more than 40 years; screen 8: newer measurements of the Antarctic Circumpolar Current, up from the classic estimate of 134 million to about 173 million cubic metres a second.

Science informs public debate and is in turn influenced by public debate; at times, there may be complex, unanticipated variables or insufficient data that may limit possible conclusions.

Screen 6: whether falling carbon dioxide or opening seaways grew the Antarctic ice sheet, and when the Drake Passage opened; screen 5: what caused the cooling during the Maunder Minimum.

Collaboration between scientists, governments, and other agencies is often required in scientific research and enterprise.

Screens 3, 4 and 7: the IPCC’s assessments; screen 6: the Ocean Drilling Program; screen 7: State of the Climate, from CSIRO and the Bureau of Meteorology.

Assessment design criteria the tasks give practice for: KA1 and KA2 (the concept questions and the checks), IAE2 and IAE3 (the heating lab, the practical, the sunspot data and the weather stations), IAE4 (evaluating the practical’s method) and KA3 (the arguments on screens 5 and 6).

How the lesson is taught

The content screens use peer instruction (Mazur, 1997; Crouch and Mazur, 2001). Each concept question targets a common misconception. Students answer alone, then try to convince a neighbour, ideally one who answered differently, then answer again; only then is the answer explained. Crouch and Mazur found that discussion moved many more students from wrong answers to right ones than the other way. Students working alone can read two short arguments, one for a common wrong answer and one for the right one, in place of a partner. Each question saves both answers, so you can see how often discussion changed students’ minds.

To run it with the class: give everyone one to two minutes to answer alone without talking, then show or ask for the spread of answers without saying which is right. If between about 35% and 70% chose the right answer, have pairs discuss for two to four minutes and answer again (Crouch and Mazur, 2001). If most are right, explain briefly and move on; if few are, teach the idea again before a second vote.

  • Lesson 1: screens 1 and 2. Use the timeline to collect students’ ideas about what changes climate.
  • Lesson 2: screens 3 and 4, the energy budget and greenhouse gases.
  • Lesson 3: screens 5 and 6, the drivers from space and from within.
  • Lesson 4: screen 7 and the Heat capacity practical.
  • Lesson 5: screens 8, 9 and 10.

Students working alone can do every screen in order.

Handle with care

  • Some students are anxious about climate change. This lesson is about natural drivers and deep time; it does not forecast. When students ask about today’s warming, acknowledge it: the IPCC figures on screen 5 show that natural drivers changed temperature by only −0.1 to +0.1 °C between 1850–1900 and 2010–2019, and the next lesson takes up the evidence and what is being done.
  • That past climates changed naturally does not mean today’s change is natural. Screen 5’s solar question makes this point with data; the next lesson develops it.
  • Safety in the practical: immersion heaters only when covered, hot water and sand can scald, and keep water away from power supplies. Follow your school’s risk assessment.

Misconceptions the screens target

  • Volcanoes made the air’s oxygen (screen 2). It came from photosynthesis.
  • The sea reflects most sunlight (screens 3 and 7). Open ocean reflects only about 7%.
  • Greenhouse gases trap all the heat, like the glass of a greenhouse (screen 4). They send some infrared back down; 239 W/m² still leaves.
  • The ozone hole causes global warming (screen 4). Ozone absorbs ultraviolet from the Sun; the greenhouse effect works on infrared from Earth. Ozone is itself a greenhouse gas.
  • A gas’s strength never changes with time (screen 4). Its global warming potential depends on the period, because gases last different times.
  • The seasons are caused by Earth’s distance from the Sun (screen 5). They are caused by the tilt; Earth is closest to the Sun in the southern summer.
  • The Sun is causing today’s warming (screen 5). Its output rises and falls with each cycle, by about 0.1% in a strong one.
  • Wind drives all ocean currents (screen 8). Deep currents are driven by density.

About the data and the pictures

  • The Darwin Airport and Tindal averages are the Bureau of Meteorology’s annual means for each station’s whole temperature record, which cover different years. The distance between the stations, about 280 km, is our calculation from their coordinates.
  • The opening picture, the air-through-time model, the planet model, the orbit model, the heating lab and the tropical Pacific are models, and each says what it simplifies. The map of Antarctica uses Natural Earth coastlines in a view looking down on the South Pole, with Australia and South America slid back for the earlier steps; real reconstructions also turn the continents. The world map’s currents are schematic.
  • Atmosphere: Britannica, Atmosphere (outgassing; volcanic gases; early carbon dioxide; oceans for at least three billion years; anaerobic first life; the ozone layer); Curtin University (2024), fresh water about four billion years ago; Geoscience Australia, Life in the rock record: Stromatolites (cyanobacteria, oxygen, the oldest fossils); UNSW (2017), Dresser Formation; Allwood and others (2007) and NASA Earth Observatory, Strelley Pool Chert; UNESCO, Shark Bay; NASA Astrobiology (2021), the Great Oxidation Event; Australian Museum, Banded iron formation; Yale News (2025), ozone; NASA, ozone poster; NOAA JetStream, the composition of dry air; NOAA Global Monitoring Laboratory, carbon dioxide in 2025. The step model draws which gases are present, not how much of each, except for today.
  • Energy budget: IPCC (2021), Working Group I, Chapter 7, Figure 7.2 and Section 7.2.1; NASA, Earth fact sheet (solar irradiance 1,361 W/m², Bond albedo 0.294, black-body 254 K, average 288 K); NASA Earth Observatory, Climate and Earth’s energy budget (29% reflected, 23% absorbed in the atmosphere); Penn State, EARTH 103 (albedo 0.31 and the albedo of Earth materials); NOAA Arctic Program, Serreze (albedo of snow, sea ice and ocean; the albedo feedback). The planet model is a one-layer model: Te = (S(1 − α)/4σ)^¼ and Ts = Te × (2/(2 − ε))^¼; its greenhouse strength is tuned to give 15 °C.
  • Greenhouse gases: Bureau of Meteorology, Climate change in Australia; CSIRO, Greenhouse: questions and answers; Australian Academy of Science (2015), The science of climate change; UCAR, Molecular vibration modes; Hong Kong Observatory (2019); NASA (2022), water vapour; US EPA, Understanding global warming potentials; IPCC (2021), Chapter 7 (methane 11.8 years, nitrous oxide 109 years) and Tables 7.15 and 7.SM.6 as listed by the GHG Protocol (2024) (GWPs; HFC-134a’s 14-year lifetime is from the chapter’s supplementary table); IPCC (2007), FAQ 10.3 (carbon dioxide); Clean Energy Regulator (Australia uses the AR5 values).
  • From space: NASA Science, Milankovitch (orbital) cycles, and Why Milankovitch cycles can’t explain Earth’s current warming; NASA Earth Observatory, Milutin Milankovitch; Stull, Practical Meteorology (eccentricity 0.0034 to 0.058; IOP Spark gives 0.005 to 0.058); NASA Space Place and StarChild (seasons; perihelion in early January); NASA Earth fact sheet; Bureau of Meteorology, Space weather and the Sun; NOAA Climate.gov, Climate change: incoming sunlight; NASA, What is the Sun’s role in climate change?; IPCC (2021), Summary for Policymakers, A.1.3. Sunspots: WDC-SILSO, Royal Observatory of Belgium, Brussels, yearly mean total sunspot number, version 2.0 (licence CC BY-NC). The orbit model uses the standard formula for daily average sunlight at the top of the atmosphere.
  • From within: Britannica (Wilson cycle; Pangaea; Rodinia); Curtin University, Decoding the Earth’s rhythms (the supercontinent cycle; Rodinia’s assembly); NOAA JetStream and Britannica (lapse rate); Raymo and Ruddiman (1992); Australian Antarctic Division, Antarctic geology (Gondwana; separation from 85 million years ago; complete about 30 million years ago; 7 cm a year); Exon, Kennett, Malone and others (2001), ODP Leg 189 summary; Livermore and others (2005); Goldner, Herold and Huber (2014); Geoscience Australia (north-east motion); NASA Earth Observatory, The carbon cycle (the slow cycle and the thermostat); University of Sydney (2024), Lloyd and others (2023) and Tasistro-Hart and others (2025), Snowball Earth (sources differ on the Sturtian’s end, 664 to 660 million years ago); International Commission on Stratigraphy, Ediacaran GSSP; UNESCO, Flinders Ranges.
  • Oceans store heat: Your Home (Australian Government), Thermal mass; OpenStax, College Physics 2e, Table 14.1 (water 4,186, granite 840 J/kg °C); Britannica, Seawater (0.932 of pure water’s); OCL journal (2012), rapeseed oil; Northern Vermont University, specific heats (quartz sand 795, granite 794); NOAA Climate.gov (2012), the top two metres of ocean; IPCC (2021), Summary for Policymakers, A.4.2; CSIRO and Bureau of Meteorology, State of the Climate 2024: Oceans; Florida Atlantic University, Land and water; Bureau of Meteorology climate averages for stations 023000 and 024048. The 4,186 is the value to give students for comparison in the practical.
  • Currents: NOAA, Ocean currents; NOAA Ocean Service, Currents tutorial (winds, the Coriolis effect, gyres, boundary currents, the conveyor belt and sea ice); NOAA JetStream, Global atmospheric circulations; University of Hawaiʻi, Ocean surface currents (depth; Ekman transport); Webb, Introduction to Oceanography (depths; 10%; deep water masses; 1,000 to 2,000 years); CSIRO (2015), the East Australian Current and the Leeuwin Current; WA Department of Primary Industries and Regional Development (the Leeuwin and the Abrolhos); Australian Antarctic Division (2002, the Antarctic Circumpolar Current; 2013, Antarctic Bottom Water); Eos (2016), Donohue and others; IPCC (2021), Summary for Policymakers, C.3.4; Bureau of Meteorology, El Niño and La Niña, ENSO history, Indian Ocean Dipole, and Climate Driver Update of 27 October 2026.

Answers at a glance

  • Concept questions: oxygen, B (photosynthesis); sea ice, A (darker ocean absorbs more); back radiation, B (infrared in all directions); methane, B (it lasts only about a decade); seasons, B (the tilt); the Sun, B (0.1%, and −0.1 to +0.1 °C); thermostat, B (more rain, more weathering); beach, A (specific heat capacity); deep currents, B (density).
  • Which gases absorb infrared: carbon dioxide, methane, water vapour, nitrous oxide and ozone absorb it; nitrogen and oxygen let it through.
  • Close the loop: volcanoes release carbon dioxide; carbonic acid falls in rain; the acid weathers rock; rivers carry the ions to the ocean; calcium carbonate settles and becomes limestone; the rock is subducted and melts, releasing carbon dioxide.
  • Planet model: with a greenhouse strength of 77%, the average temperature falls to 0 °C at an albedo of about 0.43.
  • Heating lab, 10 minutes at 50 W (30,000 J into 1 kg): water warms by 7.2 °C, seawater 7.7 °C, rapeseed oil 15.3 °C, sandstone 33.3 °C, granite 35.7 °C, quartz sand 37.7 °C.
  • Weather stations: Adelaide 21.9 − 12.1 = 9.8 °C; Renmark 25.0 − 9.8 = 15.2 °C (check q-towns: Renmark, far from the sea). Darwin Airport 32.1 − 23.3 = 8.8 °C; Tindal 34.2 − 20.6 = 13.6 °C, the same pattern.
  • What drove it: oxygen, air; Snowball Earth, plates and volcanoes; Pangaea’s dry tropics, plates and volcanoes; the hot spike 56 million years ago, air (and plates and volcanoes); the seaways round Antarctica, plates and volcanoes (and oceans); 100,000-year ice ages, Sun and orbit; few sunspots, Sun and orbit; melting sea ice, air and energy budget; Adelaide and Renmark, oceans; El Niño, oceans.
  • Exit check: x1 oxygen combining with iron; x2 the albedo rises and Earth cools; x3 absorbs more and lasts more than 100 years; x4 less tilt, farthest from the Sun in the northern summer; x5 land and ocean, currents, volcanoes and weathering; x6 water warms about five times less; x7 wind for surface currents, density for deep; x8 falling carbon dioxide and opening seaways.

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References

  • Allwood, A. C., and others (2007). 3.43 billion-year-old stromatolite reef from the Pilbara Craton of Western Australia: Ecosystem-scale insights to early life on Earth. Precambrian Research, 158, 198–227.
  • Crouch, C. H., & Mazur, E. (2001). Peer instruction: Ten years of experience and results. American Journal of Physics, 69(9), 970–977.
  • Exon, N. F., Kennett, J. P., Malone, M. J., and others (2001). Leg 189 summary. Proceedings of the Ocean Drilling Program, Initial Reports, 189.
  • Forster, P., and others (2021). The Earth’s energy budget, climate feedbacks, and climate sensitivity. In Climate change 2021: The physical science basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
  • Goldner, A., Herold, N., & Huber, M. (2014). Antarctic glaciation caused ocean circulation changes at the Eocene–Oligocene transition. Nature, 511, 574–577.
  • Hays, J. D., Imbrie, J., & Shackleton, N. J. (1976). Variations in the Earth’s orbit: Pacemaker of the ice ages. Science, 194(4270), 1121–1132.
  • IPCC (2021). Summary for policymakers. In Climate change 2021: The physical science basis. Cambridge University Press.
  • Livermore, R., and others (2005). Paleogene opening of Drake Passage. Earth and Planetary Science Letters, 236, 459–470.
  • Mazur, E. (1997). Peer instruction: A user’s manual. Prentice Hall.
  • Raymo, M. E., & Ruddiman, W. F. (1992). Tectonic forcing of late Cenozoic climate. Nature, 359, 117–122.
  • Yokoyama, Y., and others (2018). Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum. Nature, 559, 603–607.

Sources

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