Grade by Grade
A. Physical Patterns in a Changing World · Physical Patterns in a Changing World

What Shapes Climate? Natural Factors and Human Activities

A3.7About 50 minutes
Learning goals
  • I can explain how latitude, ocean currents, winds and air masses, elevation, relief and nearness to water affect climate.
  • I can use these factors to explain why two places have different climates.
  • I can describe human activities, such as burning fossil fuels and deforestation, that change climate patterns.

Words to know

ocean current
A large, steady flow of ocean water, either warm or cold, that moves in a regular path.
air mass
A huge body of air with about the same temperature and moisture throughout.
prevailing winds
The direction the wind usually blows from in a place. Most of Canada has prevailing winds from the west.
relief precipitation
Rain or snow that falls when moist air is forced to rise over mountains and cools.
rain shadow
The dry area on the side of a mountain range away from the wind.
greenhouse gas
A gas, such as carbon dioxide or methane, that traps heat in the atmosphere.
climate change
Long-term changes in Earth's climate, including the warming caused mainly by human activities that add greenhouse gases to the air.

A climate mystery

London, England, is farther north than St. John's, Newfoundland and Labrador, yet London usually has milder winters. Vancouver and Winnipeg are at almost the same latitude, but Winnipeg's January is much colder. Why?

Climate depends on more than distance from the equator. Canadian geography students often remember the main factors with the word LOWERN.

Green rainforest and dark rocks line an ocean shore, with snow only on the mountaintops behind.
The Pacific coast of British Columbia: the ocean keeps winters mild and wet, so there is green forest by the water and snow only high on the mountains. AI-generated image

LOWERN: six factors that shape climate

  • L — Latitude. Near the equator, the sun's rays hit almost straight on, so they are concentrated and it is hot. Near the poles, rays hit at a low angle and spread out, so it is cold.
  • O — Ocean currents. Warm currents warm the air above them; cold currents cool it. The warm Gulf Stream and North Atlantic Drift keep western Europe mild. The cold Labrador Current cools the coast of Newfoundland and Labrador.
  • W — Winds and air masses. Winds carry the temperature and moisture of where they came from. Most of Canada has prevailing westerly winds. Cold, dry Arctic air masses bring bitter cold in winter; warm, moist air from the Gulf of Mexico brings hot, humid summer days to Ontario.
  • E — Elevation. Air gets cooler as you go up, on average about 6.5 °C for every 1 000 m. That is why high mountains have snow even near the equator.
  • R — Relief. Mountains block and lift winds. Moist air rising up the windward side cools and drops rain or snow (relief precipitation). On the other side, the air sinks, warms and is dry: a rain shadow.
  • N — Nearness to water. Water heats up and cools down more slowly than land. Places near oceans or big lakes have milder winters and cooler summers (a maritime climate). Places far inland have bigger swings (a continental climate). The Great Lakes also cause lake-effect snow in snowbelts east of the lakes, such as near Georgian Bay and Lake Huron.
0 m25 °C1 000 m18.5 °C2 000 m12 °C3 000 m5.5 °C4 000 m−1 °CSea level 25 °C; about 6.5 °C colder for every 1 000 m up. Not to scale.
E for Elevation: if it is 25 °C at sea level, it is on average about 6.5 °C cooler for every 1 000 m you climb, so near 4 000 m it can be below freezing, even near the equator.
moist windoceanwet sidedry, warmer airdry side (rain shadow)side view, not to scale
Moist wind from the ocean rises up the windward side of the mountains, cools and drops rain. On the other side, the dry air sinks and warms, making a rain shadow. Not to scale.

Human activities change climate too

  • Burning fossil fuels (coal, oil, natural gas) for cars, heating, electricity and factories adds carbon dioxide, a greenhouse gas, to the air. Greenhouse gases trap heat, and scientists agree this is the main cause of today's global warming.
  • Deforestation (cutting down forests) removes trees that take in carbon dioxide, and burning or rotting trees releases more of it.
  • Farming produces greenhouse gases too, such as methane from cattle and rice paddies.
  • Cities create urban heat islands: pavement and buildings absorb heat, so cities are often warmer than the countryside around them.

Climate change shifts climate patterns: in many places, winters are getting milder, heat waves more common, and the Arctic is warming faster than the world average.

Worked example

Let's solve the Vancouver–Winnipeg mystery

Vancouver and Winnipeg are at almost the same latitude (about 49–50° N). Vancouver's January is usually a few degrees above 0 °C, while Winnipeg's is usually well below −10 °C. Use LOWERN to explain.

  1. L (Latitude): almost the same, so latitude can't explain the difference.
  2. N (Nearness to water): Vancouver is on the Pacific Ocean. Water cools slowly in winter, keeping the air mild. Winnipeg is in the middle of the continent, far from any ocean.
  3. W (Winds): prevailing westerly winds blow from the Pacific onto Vancouver, bringing mild, moist air. Winnipeg is often hit by cold Arctic air masses in winter.
  4. R (Relief): the Coast Mountains and Rockies block much of the mild Pacific air from reaching the Prairies.
  5. O (Ocean currents): a warm current in the North Pacific helps keep the coast mild.

Vancouver is mild because it is next to the Pacific, with westerly winds bringing ocean air. Winnipeg is cold because it is far inland, mountains block Pacific air, and Arctic air masses reach it in winter.

Just for fun

What if the Great Lakes could talk? They'd probably say: "You're welcome for the milder winters, Toronto. And sorry, Georgian Bay, about all that lake-effect snow."

Hands-on activity

Land vs. water heat test

You need: two identical cups, soil or sand, water, a sunny window or a desk lamp, and a thermometer. Do not use a heat lamp or anything hot without a grown-up.

  1. Fill one cup with soil and one with the same amount of water. Let them sit until they are both at room temperature.
  2. Measure and record the temperature of each.
  3. Put both in the sun (or under the lamp, about 30 cm away) for 20 minutes. Measure again.
  4. Move them to the shade for 20 minutes. Measure again.
  5. Which warmed up faster? Which cooled down faster?

What to look for: the soil usually warms up and cools down faster than the water. Your child connects this to N (nearness to water): places near big lakes and oceans have milder winters and cooler summers.

Your turn

1

What does each letter of LOWERN stand for?

2

Why is it hotter near the equator?

3

About how much cooler does it get for every 1 000 m you climb?

4

What is a rain shadow?

5

How does a big lake or ocean affect a nearby town's climate?

6

Which warm ocean current keeps western Europe mild?

7

Name two human activities that change climate patterns.

More practice: warm-up

1

Which direction do the prevailing winds usually blow from across most of Canada?

2

Name a cold ocean current near Canada.

3

What gas from burning fossil fuels is the main greenhouse gas added by people?

4

Does water or land heat up faster?

5

What kind of snow falls downwind of the Great Lakes?

More practice: on your own

1

Mount Kilimanjaro in Tanzania is very close to the equator but has snow near its top. Which LOWERN factor explains this?

2

The west side of the Coast Mountains in B.C. is very rainy, but parts of the B.C. interior are dry. Explain.

3

St. John's and London, England: which is farther north, and which usually has milder winters? Explain.

4

Explain how cutting down forests can affect climate.

5

Why are cities often warmer than the countryside nearby?

Challenge

1

Toronto is beside Lake Ontario; Ottawa is far from the Great Lakes. Predict which has colder winters and explain using LOWERN.

2

A city is at 0° latitude and 2 800 m elevation. A nearby city is at sea level. If the sea-level city averages 27 °C, estimate the high city's average. Show your work.

3

Explain why the Arctic warming faster than other places matters for people who live there.

Check your understanding

Quiz

1.

In LOWERN, what does the E stand for?

2.

Places near large bodies of water usually have...

3.

The dry area on the side of mountains away from the wind is a...

4.

Which current helps keep western Europe mild?

5.

The main human cause of today's global warming is...

6.

Vancouver has milder winters than Winnipeg mainly because Vancouver is...

For parents and teachers

Big idea: Expectation A3.7 asks students to describe natural processes and other factors, including human activities, that create and change climate patterns (for example ocean currents, wind, latitude, elevation, deforestation and greenhouse gas emissions). LOWERN is a common memory aid in Canadian classrooms.

How to help: Compare the weather forecast for two Canadian cities each day for a week (e.g., Vancouver and Winnipeg, or Toronto and Sudbury) and ask your child to explain differences with LOWERN. Do the land-and-water test together.

Common difficulties:

  • Thinking latitude is the only factor: the Vancouver–Winnipeg example shows it isn't.
  • Reversing the rain shadow: the windward side is wet; the leeward (sheltered) side is dry.
  • Feeling worried about climate change: acknowledge the feeling, and focus on actions people, communities and countries are taking. Keep conversations hopeful and fact-based.