B. Biology: Sustainable Ecosystems and Climate Change · Sustainable Ecosystems and Climate ChangeThe Enhanced Greenhouse Effect: How Human Activities Cause Climate Change
B2.6 B2.2 A2.4About 75 minutes
Learning goals- I can explain the difference between weather and climate.
- I can explain the natural and enhanced greenhouse effect using energy flow.
- I can identify the main greenhouse gases and the human activities that release them, in Canada and the world.
- I can use global warming potential to compare greenhouse gases.
- I can explain the evidence that recent warming is caused by humans, and describe feedback loops.
Words to know
weather
The conditions of the atmosphere at a particular place and time (today's temperature, wind, precipitation).
climate
The average weather patterns of a region over a long time, usually 30 years or more.
greenhouse gas
A gas that absorbs and re-emits infrared radiation, such as carbon dioxide, methane, nitrous oxide and water vapour.
enhanced greenhouse effect
The extra warming caused by greenhouse gases added by human activities.
global warming potential (GWP)
How much heat a gas traps over a set time (usually 100 years) compared with the same mass of carbon dioxide.
CO₂-equivalent (CO₂e)
A way to express any greenhouse gas as the amount of CO₂ that would cause the same warming.
feedback loop
A chain of effects where the result loops back to change the original cause; positive feedback amplifies change, negative feedback reduces it.
permafrost
Ground that stays frozen (at or below 0 °C) for at least two years in a row.
Remember from Grade 7
In Grade 7 Heat in the Environment you learned that greenhouse gases absorb infrared radiation, that the enhanced greenhouse effect is causing climate change, and that emissions come mainly from fossil fuels, agriculture and deforestation. In Grade 8 you learned about the albedo feedback. This lesson adds numbers and evidence: global warming potential, Canada's emissions by sector, and how scientists know humans are responsible.
Let's start with a cold snap
In January there is a week of −30 °C in Thunder Bay. Someone says, "So much for global warming!" What is wrong with this argument?
One cold week is weather: conditions at one place and time. Climate is the long-term average (usually over 30 years or more) across a region. Climate change shows up as a change in the averages and the extremes over many years and many places, not in a single day. A warmer climate can still have cold snaps; they just become less common.
The greenhouse effect: an energy balance
Earth's temperature depends on a balance between energy in and energy out:
- Sunlight (mostly visible light) passes through the atmosphere. About 30% is reflected by clouds, ice and bright surfaces; the rest is absorbed by the surface and air.
- The warm surface gives off infrared radiation (heat).
- Greenhouse gases absorb much of this infrared and re-emit it in all directions, including back down toward the surface.
- So the surface stays warmer than it would be without these gases.
This natural greenhouse effect is essential. Without it, Earth's average surface temperature would be about −18 °C instead of about +15 °C, and most life as we know it couldn't exist.
The enhanced greenhouse effect is the problem: adding more greenhouse gas holds in more energy, so more energy comes in than goes out until Earth warms enough to restore the balance. That warming changes the whole climate system.
The main greenhouse gases
| Gas | Main human sources | GWP (100 years, approximate) |
|---|
| Carbon dioxide (CO₂) | Burning fossil fuels, deforestation, cement | 1 (the reference) |
| Methane (CH₄) | Cattle digestion, landfills, oil and gas leaks, rice paddies, manure | about 28 |
| Nitrous oxide (N₂O) | Nitrogen fertilizers, manure, some industry | about 270 |
| Fluorinated gases (e.g., HFCs) | Refrigerators, air conditioners | hundreds to thousands |
| Water vapour (H₂O) | Not directly controlled by people; increases as air warms | acts as a feedback |
Where do the emissions come from?
Globally, the largest source by far is burning fossil fuels (coal, oil and natural gas) for electricity, heat, transportation and industry. Land-use change, especially clearing tropical forests, is next for CO₂. Agriculture releases much of the world's methane and nitrous oxide.
In Canada, oil and gas production is the biggest sector, followed by transportation. Canada's emissions per person are among the highest in the world, partly because of its cold climate, long travel distances and energy-intensive industries.
How do scientists know humans are the cause?
- Timing: CO₂ began rising with the Industrial Revolution and rises in step with fossil fuel use.
- Chemical fingerprint: carbon from fossil fuels has a different mix of carbon isotopes (it has no carbon-14 and less carbon-13). The CO₂ added to the air has this fossil fingerprint.
- Oxygen is decreasing very slightly, exactly as expected when carbon is burned.
- Natural causes don't fit: the Sun's energy output has not increased since the 1950s; volcanoes release far less CO₂ than humans, and big eruptions cause short-term cooling; changes in Earth's orbit act over tens of thousands of years.
- Pattern of warming: the lower atmosphere is warming while the upper atmosphere (stratosphere) is cooling, the pattern expected from more greenhouse gases, not from a brighter Sun.
The Intergovernmental Panel on Climate Change (IPCC), which reviews research from thousands of scientists, has concluded that it is unequivocal (beyond doubt) that human influence has warmed the atmosphere, ocean and land.
Feedback loops
Warming triggers changes that can amplify it (positive feedback):
- Water vapour: warmer air holds more water vapour, a greenhouse gas, which causes more warming.
- Ice–albedo: melting snow and ice expose darker surfaces that absorb more sunlight (Grade 8).
- Permafrost thaw: frozen soils in the North hold huge amounts of carbon from plants that never decomposed. As permafrost thaws, microbes release CO₂ and methane.
- Wildfires: hotter, drier conditions cause more fires, which release carbon.
Some processes slow warming (negative feedback): for example, more CO₂ can make some plants grow faster and take up more carbon. But the positive feedbacks are a major concern.
Worked exampleLet's use global warming potential
A dairy farm's cows release 12 000 kg of methane in a year. A family car releases 2 800 kg of CO₂ in a year. (a) Convert the methane to CO₂e using GWP 28. (b) How many family cars is that equal to?
- (a) CO₂e = mass × GWP = 12 000 kg × 28 = 336 000 kg CO₂e (336 tonnes).
- (b) 336 000 ÷ 2 800 = 120.
- So the methane has the same 100-year warming effect as about 120 family cars driving for a year.
336 000 kg CO₂e, about the same as 120 cars. This is why reducing methane matters (Lesson 15).
Worked exampleLet's calculate a car's emissions
Burning 1 L of gasoline releases about 2.3 kg of CO₂. A car uses 8 L per 100 km and drives 15 000 km per year. How much CO₂ does it release? What if it were replaced by a car using 5 L/100 km?
- Fuel used: 15 000 km × (8 L ÷ 100 km) = 1 200 L.
- CO₂: 1 200 L × 2.3 kg/L = 2 760 kg (about 2.8 tonnes).
- Efficient car: 15 000 × (5 ÷ 100) = 750 L; 750 × 2.3 = 1 725 kg.
- Savings: 2 760 − 1 725 = 1 035 kg per year (about 37.5% less).
About 2 760 kg of CO₂ per year; the efficient car would save about 1 035 kg per year.
Hands-on activityModel the greenhouse effect (A1.2)
You need: 2 identical clear glass jars, 2 thermometers (or one, used in turn, plus a timer), plastic wrap and an elastic band, a sunny window or a desk lamp, a ruler, dark paper.
- Put a piece of dark paper in the bottom of each jar (it absorbs light like Earth's surface). Put a thermometer in each so you can read it without moving it.
- Cover one jar with plastic wrap and an elastic band. Leave the other open.
- Record both temperatures. Then place both jars side by side in the same sunlight or the same distance (about 30 cm) from the lamp.
- Record the temperature every 2 minutes for 20 minutes. Then move them into shade and record for 10 more minutes.
- Graph both jars on the same axes.
- Analyse: which warmed faster and higher? Which cooled more slowly?
- Evaluate the model: the covered jar mostly stays warmer because the plastic stops warm air from escaping (blocks convection), which is not exactly how greenhouse gases work. How is the model like Earth's atmosphere, and how is it different?
What to look for: the covered jar usually warms more and cools more slowly. A strong evaluation says: like the atmosphere, the cover keeps energy in; unlike greenhouse gases, it mainly traps air rather than absorbing and re-emitting infrared.
Safety: don't touch a hot lamp bulb; keep the cord away from water; glass thermometers can break, so handle with care (digital ones are safest).
Just for funThe "greenhouse effect" has a misleading name. Real greenhouses stay warm mostly by stopping warm air from blowing away, not by trapping infrared the way gases do. The name stuck anyway, like a nickname from Grade 2.
Your turn
1What is the difference between weather and climate?
Weather = conditions at one place and time. Climate = the long-term average weather of a region (30 years or more).
2Why is the natural greenhouse effect good for life?
It keeps Earth's average surface temperature about +15 °C instead of about −18 °C, warm enough for liquid water and life.
3Name three greenhouse gases and one human source of each.
CO₂: burning fossil fuels (or deforestation). CH₄: cattle, landfills, gas leaks. N₂O: nitrogen fertilizers. (Also HFCs from refrigerants.)
4What does a GWP of 28 for methane mean?
Over 100 years, 1 kg of methane traps about 28 times as much heat as 1 kg of CO₂.
5Give two pieces of evidence that recent warming is caused by humans.
Any two: CO₂ rise matches fossil fuel use; the extra CO₂ has a fossil-fuel isotope fingerprint; the Sun's output hasn't increased; the stratosphere is cooling while the lower atmosphere warms; volcanoes and orbit changes don't fit.
6Which sector produces the most greenhouse gas in Canada? The second most?
Oil and gas (about 30%); then transport (about 22%).
7Explain the permafrost feedback loop.
Warming thaws permafrost → microbes decompose old frozen plant matter → CO₂ and methane are released → more warming → more thawing.
More practice: warm-up
1What kind of radiation does Earth's warm surface give off?
Infrared radiation (heat).
2What does CO₂e stand for?
Carbon dioxide equivalent.
3Which greenhouse gas comes from rice paddies and landfills?
4What does IPCC stand for?
Intergovernmental Panel on Climate Change.
5Is a single cold winter proof that climate is not warming? Why?
No. One winter is weather; climate is a long-term average over many years and places.
More practice: on your own
1A landfill releases 500 tonnes of methane per year. Capturing it and burning it for electricity turns it into CO₂ (500 tonnes of methane makes about 1 375 tonnes of CO₂). Compare the CO₂e before and after.
Before: 500 × 28 = 14 000 t CO₂e. After: about 1 375 t CO₂e. Capturing and burning the methane cuts the warming effect by about 90% (and makes electricity).
2Use the bar chart: what fraction of Canada's emissions come from oil and gas plus transport together?
207.6 + 151.4 = 359.0 Mt out of 684.8 Mt ≈ 52%, just over half.
3Explain why water vapour is called a feedback rather than a driver of climate change.
People don't directly control the amount of water vapour in the air; it depends on temperature. When CO₂ warms the air, it holds more water vapour, which causes more warming: it amplifies the change rather than starting it.
4Why does deforestation add to climate change in two ways?
1. Burning or decomposing the trees releases their carbon as CO₂. 2. The forest can no longer act as a carbon sink, taking CO₂ out of the air.
5A car drives 20 000 km a year using 7 L/100 km. Using 2.3 kg CO₂/L, how much CO₂ does it release?
Fuel: 20 000 × 7 ÷ 100 = 1 400 L. CO₂: 1 400 × 2.3 = 3 220 kg (about 3.2 tonnes).
Challenge
1Explain, using energy flow, why adding greenhouse gases causes warming even though the Sun's output hasn't changed.
Energy in from the Sun stays about the same, but more greenhouse gas means less infrared energy escapes to space. Energy in is now greater than energy out, so energy accumulates in the Earth system (mostly in the ocean), and temperatures rise until Earth gives off enough infrared to rebalance.
2Methane has a much higher GWP than CO₂, yet CO₂ is called the main cause of climate change. Explain.
Humans release far more CO₂ (by mass) than methane, and CO₂ stays in the air for centuries, while methane breaks down in about a decade. So CO₂'s total effect is larger and longer lasting, even though each kilogram of methane is more powerful. (Cutting methane still gives a fast benefit.)
3A classmate says, "Volcanoes release more CO₂ than people, so humans can't be the cause." Respond with evidence.
Incorrect: human activities release much more CO₂ each year than all volcanoes combined (volcanoes release roughly 1% as much, based on scientific estimates). Big eruptions actually cause short-term cooling (sulfur droplets reflect sunlight). And the extra CO₂ in the air has a fossil-fuel isotope fingerprint, not a volcanic one.
Quiz
1. Which statement describes CLIMATE?
2. Without the natural greenhouse effect, Earth's average temperature would be about...
3. What do greenhouse gases absorb?
4. 5 tonnes of methane (GWP 28) is equivalent to how much CO₂?
5. Which is Canada's largest emitting sector?
6. Which is a POSITIVE feedback that speeds up warming?
7. Which evidence best shows that the extra CO₂ comes from fossil fuels?
Big idea (B2.6, analyse how human activities contribute): burning fossil fuels, clearing forests and agriculture add greenhouse gases that strengthen the natural greenhouse effect, upsetting Earth's energy balance and the carbon cycle (B2.2). Multiple independent lines of evidence point to human causes, and feedbacks amplify the warming. Working with real Canadian emissions data and GWP builds scientific literacy (A2.4).
How to help: Look at a fuel bill or car's fuel use together and estimate your household's CO₂ using 2.3 kg per litre of gasoline. Keep the conversation hopeful: the next lessons focus on solutions.
Common difficulties:
- Confusing the greenhouse effect with the ozone hole. They are different problems: the ozone layer blocks ultraviolet light.
- Weather versus climate. Use the "one day vs. 30-year average" rule.
- Thinking GWP alone decides importance. Amount released and lifetime matter too.
- Feeling anxious. It's normal; point to actions and progress (Lessons 12 to 15).
Sources: Canada's 2024 emissions by sector (Environment and Climate Change Canada, Greenhouse gas emissions indicator); GWP values from IPCC assessments (methane about 28, nitrous oxide about 265 to 273 over 100 years); natural greenhouse effect temperatures (NASA); IPCC Sixth Assessment Report ("unequivocal").