D. Earth and Space Science: Climate Change · Climate Change

Earth's Climate System: Sun, Air, Oceans, Ice and Land

D3.1 D2.1 A1.12 A2.1About 70 minutes

Learning goals

I can describe the principal components of Earth's climate system: the Sun, atmosphere, oceans (hydrosphere), ice (cryosphere), land and living things.
I can explain how latitude and the angle of sunlight cause uneven heating of Earth.
I can use albedo to calculate how much solar energy a surface absorbs.
I can explain how the shape and arrangement of land masses (topography and configuration) affect climate.
I can use key terms correctly: climate system, albedo, heat sink, atmosphere, hydrosphere, anthropogenic.

Words to know

climate
The average weather conditions, and their usual range, in a region over a long time (usually 30 years or more).

climate system
The Sun, atmosphere, hydrosphere, cryosphere, lithosphere and biosphere, and all the ways they exchange energy and matter.

atmosphere
The layer of gases surrounding Earth.

hydrosphere
All of Earth's water: oceans, lakes, rivers, groundwater and water vapour.

cryosphere
The frozen parts of Earth: sea ice, glaciers, ice sheets, snow and permafrost.

albedo
The fraction of incoming sunlight that a surface reflects, from 0 (absorbs everything) to 1 (reflects everything).

heat sink
A part of the climate system that absorbs and stores large amounts of heat, such as the ocean.

topography
The shape and height of the land surface: mountains, valleys, plains.

anthropogenic
Caused or produced by humans.

Let's start with a puzzle

Vancouver and Thunder Bay are at almost the same latitude: both are a little south of 50° N. Yet in January, Vancouver usually has rain and temperatures a few degrees above freezing, while Thunder Bay is usually well below −10 °C with snow on the ground.

Same Sun, same distance from the equator, very different winters. To explain this, you need to see climate as a system: the Sun supplies the energy, and the air, oceans, ice and land decide where that energy goes. By the end of this unit you will be able to explain the Vancouver–Thunder Bay puzzle completely, and you will understand why adding greenhouse gases changes the whole system.

Remember from Grade 9

In Grade 9 (Sustainable Ecosystems and Climate Change) you learned the difference between weather and climate, the four spheres (biosphere, hydrosphere, lithosphere, atmosphere), the basic greenhouse effect, and the main indicators of climate change. In Grade 10 you go deeper: how energy moves through the climate system, how scientists reconstruct past climates, how they test hypotheses with data, and how well our solutions are working.

The components of the climate system

Scientists describe Earth's climate system as several connected parts. Each part stores energy, moves it, or changes how much sunlight is absorbed.

The Sun is the energy source. Almost all the energy that drives weather and climate arrives as sunlight. (Heat from Earth's interior is tiny by comparison.)
The atmosphere is the thin layer of gases around Earth. It is mostly nitrogen (about 78%) and oxygen (about 21%), with small amounts of argon, water vapour, carbon dioxide and other gases. Clouds reflect sunlight; greenhouse gases absorb heat given off by the surface; winds carry heat from place to place.
The hydrosphere, especially the oceans, covers about 71% of Earth's surface. Water can absorb huge amounts of heat with only a small temperature change, so the ocean is Earth's biggest heat sink. Ocean currents carry warm water toward the poles and cold water toward the equator.
The cryosphere (snow, sea ice, glaciers, ice sheets and permafrost) reflects a lot of sunlight and stores fresh water.
The lithosphere (land): its topography (mountains, plains) and the configuration of land masses (where the continents are) steer winds and ocean currents.
The biosphere (living things) exchanges carbon dioxide, water vapour and other gases with the air, and changes how dark or bright the surface is.

The climate system: energy from the Sun is absorbed, reflected and moved around by the atmosphere, oceans, ice, land and living things. Bright ice reflects most of the sunlight that reaches it; dark ocean absorbs most of it (not to scale).

Why the energy is uneven: latitude and the angle of sunlight

Earth is a sphere, so sunlight hits it at different angles. Near the equator, the noon Sun is high in the sky and its rays strike the ground nearly straight on. Near the poles, the Sun stays low and the rays strike at a shallow angle.

A beam of sunlight carries a fixed amount of energy. When it hits the ground at a low angle, the same energy is spread over more ground, so each square metre receives less. A low Sun's light also travels through more atmosphere, so more of it is scattered and absorbed on the way.

The result: the tropics receive much more solar energy per square metre than the poles. This uneven heating is what drives winds and ocean currents, which you will study in the next lessons.

Earth's axis is tilted about 23.4°. As Earth orbits the Sun, each hemisphere takes turns leaning toward the Sun. That changes the noon Sun angle and the length of the day, which gives us seasons.

The same beam of sunlight carries the same energy in both pictures. When the Sun is low, the beam spreads over twice as much ground (1 ÷ sin 30° = 2), so each square metre gets half the energy. This is the main reason high latitudes and winters are colder.

Worked example

Example 1: The noon Sun in Toronto

Toronto is at about 43.7° N. Find the height of the noon Sun above the horizon (its elevation angle) on the June solstice and the December solstice. Then compare how much ground a beam of sunlight covers.

At the equinoxes (March and September), the noon Sun's elevation = 90° − latitude = 90° − 43.7° = 46.3°.
On the June solstice the Northern Hemisphere tilts toward the Sun, so add the tilt: 46.3° + 23.4° = 69.7°.
On the December solstice it tilts away, so subtract: 46.3° − 23.4° = 22.9°.
A beam with a cross-section of 1 m² covers 1 ÷ sin(elevation) square metres of flat ground.
June: 1 ÷ sin 69.7° = 1 ÷ 0.938 ≈ 1.07 m². December: 1 ÷ sin 22.9° = 1 ÷ 0.389 ≈ 2.57 m².
So in December the same beam is spread over about 2.57 ÷ 1.07 ≈ 2.4 times as much ground, and each square metre gets less than half the energy.

June noon Sun ≈ 70°, December noon Sun ≈ 23°. December sunlight is spread over about 2.4 times more ground per beam, and the days are also much shorter. Both effects make winter cold.

Albedo: how much sunlight is reflected

Albedo is the fraction of incoming sunlight that a surface reflects. It runs from 0 (a perfectly black surface that absorbs everything) to 1 (a perfect mirror). Whatever is not reflected is absorbed and warms the surface.

Absorbed energy = incoming energy × (1 − albedo)

Earth as a whole reflects about 30% of incoming sunlight (an albedo of about 0.3), mostly from clouds, ice and snow.

Typical albedo values (real surfaces vary; for example, old dirty snow reflects less than fresh snow). An albedo of 0.85 means 85% of the sunlight is reflected and only 15% is absorbed.

Worked example

Example 2: Sea ice versus open water

Bright summer sunlight delivers about 500 W/m² (watts per square metre) to the surface of the Arctic Ocean. Compare the energy absorbed by 1 m² of sea ice (albedo 0.6) and 1 m² of open ocean (albedo 0.06).

Sea ice absorbs 1 − 0.6 = 0.4 of the sunlight: 500 × 0.4 = 200 W/m².
Open ocean absorbs 1 − 0.06 = 0.94 of the sunlight: 500 × 0.94 = 470 W/m².
Ratio: 470 ÷ 200 = 2.35. Open water absorbs more than twice as much energy.
When sea ice melts, dark water is exposed, which absorbs more energy, which melts more ice. This is the ice–albedo feedback, a positive feedback you met in Grade 9.

Sea ice: 200 W/m². Open ocean: 470 W/m², about 2.35 times as much.

Land: topography and the configuration of land masses

The solid Earth matters too:

Mountains block and lift moving air. Air forced up a mountain cools and drops rain or snow on the windward side, leaving a dry rain shadow on the other side (Lesson 4). The Coast Mountains of British Columbia are an example.
Elevation: air gets colder with height in the lowest part of the atmosphere, so high places are colder than nearby lowlands.
Configuration of land masses: where the continents are decides which way ocean currents can flow and how far a place is from the sea. The middle of a large continent (like central Canada) has hot summers and very cold winters. A coast has milder seasons because water heats and cools slowly.
Over millions of years, plate tectonics slowly move the continents, which changes ocean currents and climate (Lesson 9).

Now you can solve the opening puzzle: Vancouver sits on the Pacific coast with mild ocean air blowing onshore from the west, and mountains that block much of the cold Arctic air coming from the interior. Thunder Bay sits in the middle of the continent, far from any ocean, open to cold Arctic air in winter. (Lake Superior moderates it a little, but a lake freezes over in many winters, while the Pacific does not.)

Key terms for this unit

You will use these terms all unit (expectation D2.1). Learn them now:

Anthropogenic: caused by humans (from Greek anthropos, human, and genesis, origin). "Anthropogenic emissions" are emissions from human activities.
Atmosphere, hydrosphere, cryosphere, lithosphere, biosphere: the parts of the climate system.
Albedo: fraction of sunlight reflected.
Heat sink: something that absorbs and stores a lot of heat (the ocean is the biggest one).
Cycles: repeating processes, such as the water cycle, the carbon cycle and the 11-year sunspot cycle.
Feedback: a change that causes further changes, which either strengthen it (positive) or weaken it (negative).

Just for fun

Fresh snow can reflect around 85% of the sunlight that hits it. That makes a snowy Canadian field one of the best natural mirrors on the planet, which is why you can get a sunburn while skiing in March.

Careers: who studies the climate system?

Meteorologists forecast weather days ahead. Environment and Climate Change Canada employs meteorologists who issue forecasts and weather warnings across the country.
Climatologists and climate scientists study long-term patterns and build computer climate models.
Oceanographers measure ocean temperature, salt and currents, using ships, buoys and floating robots.
Glaciologists measure glaciers and ice sheets.
Remote sensing specialists use satellite data to measure snow, ice, vegetation and sea level.

Most of these careers start with a university degree in physics, geography, environmental science, mathematics or engineering. Grade 11 and 12 physics, chemistry and math keep these doors open.

Hands-on activity

Investigate albedo with a home experiment (A1.12)

You need: two identical cans or jars, one sheet of white paper and one of black paper (or dark and light cloth), tape, two thermometers (digital kitchen thermometers work well), a sunny window or a desk lamp, a timer, graph paper.

Wrap one jar in white paper and one in black paper. Fill both with the same amount of room-temperature water.
Record the starting temperature of each.
Put both in the same sunlight (or the same distance, about 30 cm, from the lamp).
Record both temperatures every 3 minutes for 30 minutes in a data table with units (°C, min).
Graph both lines on the same axes: time on the x-axis, temperature on the y-axis. Label axes and give the graph a title.
Analyse: which jar warmed more? Calculate the temperature change (final − initial) for each.
Connect: which jar is like sea ice, and which is like open ocean? What happens to warming if Arctic ice keeps shrinking?

What to look for: the black jar should warm more. A strong answer uses numbers (for example, "the black jar rose 6.5 °C and the white jar rose 3.0 °C") and links the result to albedo.

Safety: a desk lamp bulb gets hot; do not touch it, and keep water away from the cord and plug. A grown-up should help set up the lamp.

Your turn

Name the six main components of the climate system described in this lesson.

What does anthropogenic mean? Give one example of an anthropogenic greenhouse gas emission.

Why is the ocean called Earth's biggest heat sink?

A parking lot has an albedo of 0.08. What percentage of sunlight does it absorb?

Explain in two sentences why the poles receive less solar energy per square metre than the equator.

How does the configuration of land masses affect climate? Give one example.

Which has a higher albedo: a dark green spruce forest or a snow-covered field? What does this mean for which one warms faster in spring sunshine?

More practice: warm-up

What is the source of almost all the energy in Earth's climate system?

What is the albedo of a surface that reflects all the light that hits it? One that absorbs all of it?

Which part of the climate system includes glaciers, sea ice and permafrost?

About what fraction of incoming sunlight does Earth reflect overall?

By about how many degrees is Earth's axis tilted?

More practice: on your own

Sunlight delivers 600 W/m² to a field of fresh snow (albedo 0.85) and to a grassy field (albedo 0.25). How much does each absorb per square metre?

Find the noon Sun elevation in Ottawa (about 45.4° N) at the equinox and at the December solstice.

A beam of sunlight with a 1 m² cross-section hits flat ground when the Sun is 30° above the horizon. What area of ground does it cover? How does the energy per square metre compare with an overhead Sun?

Explain how topography can make two towns only 100 km apart have very different precipitation.

A student says, "Ice and snow are just water, so they're part of the hydrosphere, not a separate part of the climate system." How would you respond?

Challenge

At the North Pole (90° N), what is the noon Sun elevation on the June solstice? On the December solstice? What does this tell you about Arctic seasons?

Arctic sea ice (albedo 0.6) shrinks by 1 million km² in a summer, replaced by open ocean (albedo 0.06). If the average sunlight reaching the surface is 200 W/m², how much extra power is absorbed? (1 km² = 1 000 000 m²)

Use the climate system components to explain why Vancouver's January is much milder than Thunder Bay's, even though they are at similar latitudes. Mention at least three components.

Check your understanding

Quiz

Which part of the climate system stores the most heat?

What does albedo measure?

A surface with albedo 0.2 receives 400 W/m² of sunlight. How much does it absorb?

Why do high latitudes receive less solar energy per square metre?

Which word means "caused by humans"?

Which is an example of the configuration of land masses affecting climate?

For parents and teachers

Big idea: Climate is a system. The Sun supplies energy, and the atmosphere, oceans, ice, land and living things store it, move it and reflect it. This lesson sets up the vocabulary for the whole unit (expectation D2.1) and the components of the climate system (D3.1).

How to help: Ask your teen to explain the Vancouver–Thunder Bay puzzle in their own words at the end. On a sunny day, compare how warm a dark car and a light car feel, or a dark driveway and a light sidewalk, and ask which has the higher albedo. If your teen finds the trigonometry in the Sun-angle examples hard, they can use a calculator's sin key in degree mode; the key idea is that a low Sun spreads energy over more ground.

Common difficulties:

Thinking seasons happen because Earth is closer to the Sun in summer. (Earth is actually closest to the Sun in early January.) Seasons come from the tilt.
Mixing up albedo (reflected) and absorbed: absorbed = 1 − albedo.
Forgetting that the ocean stores far more heat than the air.

Safety: the activity uses a desk lamp; supervise around hot bulbs and keep water away from cords.