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SNC2D · Unit 3 test review

Climate Change: Test Review

Everything for the Unit 3 test on one page: the key facts from all 8 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

Weather, Climate and Earth's Climate System

  • Weather is the short-term state of the atmosphere; climate is the long-term average and range, normally over 30 years.
  • The climate system: atmosphere, hydrosphere, cryosphere, lithosphere and biosphere, powered by energy from the Sun.
  • Albedo is the fraction of sunlight reflected (0 to 1); anthropogenic means caused by humans; a heat sink stores heat with little temperature change.
  • Local climate depends on latitude, nearness to water, ocean currents, prevailing winds, elevation and mountain barriers.
  • Köppen groups: A tropical, B dry, C temperate, D continental, E polar. Most of Ontario is D.
  • Ontario's ecozones: Mixedwood Plains, Boreal Shield and Hudson Plains.

Heat Transfer in the Atmosphere and Hydrosphere

  • Heat flows from warmer to cooler matter by radiation (waves, no medium needed), conduction (contact) or convection (moving fluid).
  • The Sun heats the surface by radiation; the surface heats the air by conduction; convection carries the heat upward.
  • Water's specific heat capacity, about 4.18 J/(g·°C), is roughly five times that of sand, so water warms and cools slowly.
  • : for the same energy and mass, a substance with a larger changes temperature less.
  • Wind blows from high pressure to low pressure; sea breezes blow from water to land by day and land breezes from land to water at night.
  • Over Canada the prevailing winds are westerlies, and weather usually moves from west to east.

The Natural and Anthropogenic Greenhouse Effect

  • Sunlight arrives as shortwave radiation; Earth's surface gives off longwave infrared radiation.
  • Earth's average albedo is about 0.30: about 30% of incoming sunlight is reflected to space.
  • Greenhouse gases (H₂O, CO₂, CH₄, N₂O, O₃, halocarbons) absorb infrared and re-emit part of it back toward the surface.
  • The natural greenhouse effect raises Earth's average temperature from about −18 °C to about 15 °C.
  • Human emissions have raised CO₂ from about 280 ppm to over 420 ppm, strengthening the greenhouse effect and warming Earth.
  • Reflected energy = albedo × incoming energy; absorbed energy = (1 − albedo) × incoming energy.

Greenhouse Gases: Sources, Sinks and the Carbon Cycle

  • A source releases a greenhouse gas; a sink removes and stores it. Concentration rises when sources exceed sinks.
  • Main human sources: fossil fuels and cement (CO₂), livestock, landfills and fossil fuel leaks (CH₄), fertilizers (N₂O), refrigerants (halocarbons).
  • GWP compares warming per tonne with CO₂ over 100 years: CO₂ = 1, CH₄ ≈ 28, N₂O ≈ 270, some halocarbons thousands.
  • About half of human CO₂ emissions stay in the air; the rest is taken up roughly equally by oceans and land.
  • Canada: about 694 Mt CO₂e in 2023, about 1.5% of world emissions, but among the highest per person.

Evidence of Past and Present Climate Change

  • Proxies (ice cores, tree rings, lake and ocean sediments, fossils) record past climate; ice-core bubbles preserve samples of ancient air.
  • Natural factors: plate tectonics, uplift and weathering, orbital cycles, solar output and volcanoes; each acts on its own time scale.
  • Long-term global warming is about 1.3–1.4 °C above pre-industrial (1850–1900); Canada has warmed about 1.7 times as fast since 1948 (almost twice as fast since 1970), and the North more than twice as fast.
  • Indicators: rising temperature and sea level, shrinking Arctic sea ice and glaciers, changing weather extremes, rising CO₂ in the carbon budget.
  • Correlation is not causation: a causal claim also needs a mechanism and the ruling out of other explanations.

Oceans, Water and Climate Patterns

  • The oceans have absorbed about 90% of the extra heat trapped by the enhanced greenhouse effect; they are Earth's largest heat sink.
  • Large bodies of water moderate climate: cooler summers, milder winters and a later, longer fall nearby.
  • Surface currents are driven by wind; deep (thermohaline) currents by differences in temperature and salinity, which affect density.
  • Warm currents warm and moisten nearby coasts; cold currents cool and dry them.
  • Positive feedbacks amplify a change (ice-albedo, water vapour, permafrost); negative feedbacks reduce it (more outgoing infrared from a warmer Earth).
  • Melting land ice raises sea level; melting floating sea ice barely does.

Ozone Depletion, Ground-Level Ozone and Smog

  • Ozone (O₃) is good up high (stratospheric ozone absorbs UV) and bad nearby (ground-level ozone is a pollutant in smog).
  • CFCs release chlorine in the stratosphere, and each chlorine atom can destroy many thousands of ozone molecules because it is regenerated.
  • The 1987 Montreal Protocol and its later amendments have phased out about 99% of ozone-depleting substances; the ozone layer is projected to recover by about 2040–2066 depending on region.
  • Ground-level ozone forms when NOₓ and VOCs react in sunlight; smog is ozone plus fine particles.
  • The ozone hole lets in more UV; the enhanced greenhouse effect traps more infrared. They are different problems.

Impacts of Climate Change and How We Respond

  • Global impacts include heat waves, drought and desertification, coastal flooding, glacier loss and coral bleaching.
  • In Canada: shrinking Arctic sea ice (polar bears, Inuit travel and hunting), thawing permafrost, larger wildfires, coastal erosion, and longer but less predictable growing seasons.
  • Mitigation reduces emissions or increases sinks; adaptation copes with changes that can no longer be avoided.
  • Canada's stated targets: 40–45% below 2005 emissions by 2030 and net-zero by 2050. The consumer carbon price was set to zero in April 2025; industrial carbon pricing continues.
  • The IPCC assesses climate science for governments; the Paris Agreement (2015) aims to keep warming well below 2 °C and pursue 1.5 °C.
  • Judge a claim by its source, purpose, evidence, balance and consistency with other reliable sources.

Where marks get lost

  • Using one day or one season as evidence about climate ("it's freezing today, so where is global warming?"). Climate is a 30-year average; a cold day is weather. (Weather, Climate and Earth's Climate System)
  • Thinking climate means only temperature. Climate also includes precipitation, humidity, wind and how all of these vary through the year. (Weather, Climate and Earth's Climate System)
  • Explaining every difference between two places by latitude. Two cities at the same latitude can have very different climates because of oceans, winds, elevation and mountains. (Weather, Climate and Earth's Climate System)
  • Forgetting the cryosphere and biosphere. Ice and living things are part of the climate system: ice reflects sunlight and plants remove carbon dioxide. (Weather, Climate and Earth's Climate System)
  • Saying "cold flows in". Only heat (thermal energy) is transferred, and on its own it always flows from the warmer object to the cooler one. (Heat Transfer in the Atmosphere and Hydrosphere)
  • Thinking the air is heated mainly by sunlight passing through it. Most sunlight passes through the air; the ground absorbs it and then heats the air from below. (Heat Transfer in the Atmosphere and Hydrosphere)
  • Mixing up which way a sea breeze blows. By day the breeze blows from the water toward the warmer land; at night it reverses. (Heat Transfer in the Atmosphere and Hydrosphere)
  • Assuming radiation needs air or water to travel. Radiation crosses empty space, which is how sunlight reaches Earth. (Heat Transfer in the Atmosphere and Hydrosphere)
  • Confusing temperature with thermal energy. A bathtub of warm water has more thermal energy than a cup of boiling water, even though its temperature is lower. (Heat Transfer in the Atmosphere and Hydrosphere)
  • Saying the greenhouse effect is bad. The natural greenhouse effect keeps Earth habitable; the problem is the extra, human-made enhancement of it. (The Natural and Anthropogenic Greenhouse Effect)
  • Blaming global warming on the ozone hole. The ozone hole lets in more ultraviolet radiation, which is a health risk, but it is a separate problem; warming comes from greenhouse gases trapping infrared. (The Natural and Anthropogenic Greenhouse Effect)
  • Saying greenhouse gases trap incoming sunlight. Most incoming sunlight passes through them; they absorb the outgoing longwave infrared from Earth's surface. (The Natural and Anthropogenic Greenhouse Effect)
  • Thinking CO₂ cannot matter because it is only about 0.04% of the air. The main gases, N₂ and O₂, absorb almost no infrared, so trace gases control the effect. (The Natural and Anthropogenic Greenhouse Effect)
  • Saying greenhouse gases "reflect" heat back down. They absorb infrared and then re-emit it in all directions; that is different from reflection. (The Natural and Anthropogenic Greenhouse Effect)
  • Thinking methane is the main cause of warming because its GWP is high. Per tonne it is stronger, but CO₂ is emitted in far larger amounts and lasts much longer, so CO₂ causes most human-caused warming. (Greenhouse Gases: Sources, Sinks and the Carbon Cycle)
  • Saying volcanoes emit more CO₂ than people. Human activities emit roughly 100 times more CO₂ each year than all the world's volcanoes. (Greenhouse Gases: Sources, Sinks and the Carbon Cycle)
  • Treating water vapour as something people directly control. Its amount is set by temperature, so it acts as a feedback that amplifies warming caused by other gases. (Greenhouse Gases: Sources, Sinks and the Carbon Cycle)
  • Assuming a sink removes carbon forever. Forests can burn or be cut, and warming oceans absorb less CO₂, so stored carbon can return to the air. (Greenhouse Gases: Sources, Sinks and the Carbon Cycle)
  • Mixing up GWP and concentration. GWP compares warming per tonne; it does not tell you how much of a gas is in the air. (Greenhouse Gases: Sources, Sinks and the Carbon Cycle)
  • Treating correlation as proof of causation. Two trends rising together is a starting point; you also need a mechanism and to rule out other causes. (Evidence of Past and Present Climate Change)
  • Saying "the climate has always changed, so this change is natural." Past changes had causes too; today's natural factors (Sun, orbit, volcanoes) do not explain the current rapid warming, and greenhouse gases do. (Evidence of Past and Present Climate Change)
  • Thinking one record-breaking year means the Paris 1.5 °C limit has been passed. The Paris goal refers to long-term warming averaged over about 20 years, not a single year. (Evidence of Past and Present Climate Change)
  • Reading a narrow tree ring as "cold" every time. Narrow rings mean poor growth, which can come from drought, cold, insects or damage; check other records. (Evidence of Past and Present Climate Change)
  • Assuming the outermost tree ring or the top of an ice core is the oldest. In both, the newest layer is on the outside or on top, and age increases inward or downward. (Evidence of Past and Present Climate Change)
  • Thinking "positive feedback" means a good outcome. Positive means the change is amplified; the ice-albedo feedback is positive and makes warming worse. (Oceans, Water and Climate Patterns)
  • Saying melting Arctic sea ice is the main cause of sea-level rise. Floating ice barely changes sea level; melting land ice and the expansion of warming seawater are the main causes. (Oceans, Water and Climate Patterns)
  • Assuming the ocean absorbing heat solves the problem. The stored heat expands seawater, intensifies storms, melts ice from below and drives marine heat waves. (Oceans, Water and Climate Patterns)
  • Saying lake-effect snow falls on the upwind side of a lake. It falls downwind, where the moistened air rises and cools. (Oceans, Water and Climate Patterns)
  • Thinking deep ocean currents are driven by wind. Wind drives surface currents; deep currents are driven by density differences from temperature and salinity. (Oceans, Water and Climate Patterns)
  • Saying the ozone hole causes global warming. The ozone hole lets more ultraviolet reach the ground; global warming comes from greenhouse gases trapping infrared. (Ozone Depletion, Ground-Level Ozone and Smog)
  • Thinking all ozone is good, or all ozone is bad. Stratospheric ozone protects us; ground-level ozone is a pollutant. (Ozone Depletion, Ground-Level Ozone and Smog)
  • Saying smog is released straight from tailpipes. Cars emit NOₓ and VOCs; ground-level ozone forms afterward when those react in sunlight. (Ozone Depletion, Ground-Level Ozone and Smog)
  • Calling the ozone hole a literal hole with no ozone. It is a region of severe thinning that forms each southern spring over Antarctica. (Ozone Depletion, Ground-Level Ozone and Smog)
  • Assuming the ozone problem is already fixed. Ozone-depleting chemicals last for decades, so full recovery is expected only around 2040–2066. (Ozone Depletion, Ground-Level Ozone and Smog)
  • Mixing up mitigation and adaptation. Mitigation tackles the cause (emissions); adaptation deals with the effects. (Impacts of Climate Change and How We Respond)
  • Treating every source as equal. A peer-reviewed study or IPCC report is checked by experts; a viral post or an advertisement is not. (Impacts of Climate Change and How We Respond)
  • Assuming that because one extreme event cannot be blamed on climate change alone, climate change has no effect on it. Scientists measure how warming changes the odds and intensity of such events. (Impacts of Climate Change and How We Respond)
  • Saying Ontario still requires Drive Clean tests for cars. Testing of light vehicles ended in April 2019; the program now targets heavy-duty diesel vehicles. (Impacts of Climate Change and How We Respond)
  • Thinking that "some benefits" (like longer growing seasons) cancel the harms. Longer seasons come with droughts, floods, pests and heat stress, and the harms fall hardest on vulnerable communities. (Impacts of Climate Change and How We Respond)

Practice test

24 questions from across the unit. Each one shows the lesson it comes from.

  1. Weather, Climate and Earth's Climate System
    1
    Which statement describes climate rather than weather?
  2. Weather, Climate and Earth's Climate System
    2
    Halifax and Ottawa are at similar latitudes, but Halifax has milder winters and cooler summers. What is the best explanation?
  3. Weather, Climate and Earth's Climate System
    3
    Which term means "caused by human activity"?
  4. Heat Transfer in the Atmosphere and Hydrosphere
    4
    How does energy from the Sun reach Earth?
  5. Heat Transfer in the Atmosphere and Hydrosphere
    5
    On a clear night beside a large lake, which way does the breeze usually blow, and why?
  6. Heat Transfer in the Atmosphere and Hydrosphere
    6
    Why do weather systems in Ontario usually arrive from the west?
  7. The Natural and Anthropogenic Greenhouse Effect
    7
    Which kind of radiation do greenhouse gases mainly absorb?
  8. The Natural and Anthropogenic Greenhouse Effect
    8
    Put the steps of the greenhouse effect in order.
    1. 1Greenhouse gases re-emit infrared, part of it back toward the surface
    2. 2Greenhouse gases absorb some of the infrared
    3. 3The warm surface emits longwave infrared radiation
    4. 4Shortwave sunlight passes through the atmosphere
    5. 5The surface absorbs sunlight and warms
  9. The Natural and Anthropogenic Greenhouse Effect
    9
    If greenhouse gas concentrations stopped rising today, what would happen to Earth's energy budget right away?
  10. Greenhouse Gases: Sources, Sinks and the Carbon Cycle
    10
    Match each greenhouse gas to a major human source.
    Carbon dioxide
    Methane
    Nitrous oxide
    Halocarbons
  11. Greenhouse Gases: Sources, Sinks and the Carbon Cycle
    11
    Which of these is a carbon sink?
  12. Greenhouse Gases: Sources, Sinks and the Carbon Cycle
    12
    Which statement about Canada's greenhouse gas emissions is accurate?
  13. Evidence of Past and Present Climate Change
    13
    Match each proxy to what it mainly reveals about past climate.
    Air bubbles in an ice core
    Tree-ring widths
    Pollen in lake sediments
    Fossil corals in Ontario rock
  14. Evidence of Past and Present Climate Change
    14
    Which observation helps rule out the Sun as the main cause of recent warming?
  15. Evidence of Past and Present Climate Change
    15
    The WMO reported that 2024 was about 1.55 °C above the pre-industrial average. Which statement is accurate?
  16. Oceans, Water and Climate Patterns
    16
    Where has most of the extra heat trapped by the enhanced greenhouse effect gone?
  17. Oceans, Water and Climate Patterns
    17
    Put the ice-albedo feedback loop in order, starting from the initial warming.
    1. 1Temperature rises further
    2. 2Albedo decreases, so more sunlight is absorbed
    3. 3Darker ocean and land are exposed
    4. 4Global temperature rises
    5. 5Snow and sea ice melt
  18. Oceans, Water and Climate Patterns
    18
    Why are fruit orchards and vineyards concentrated near Lake Ontario on the Niagara Peninsula?
  19. Ozone Depletion, Ground-Level Ozone and Smog
    19
    What does the stratospheric ozone layer protect living things from?
  20. Ozone Depletion, Ground-Level Ozone and Smog
    20
    Under which conditions is ground-level ozone most likely to reach unhealthy levels in Ontario?
  21. Ozone Depletion, Ground-Level Ozone and Smog
    21
    What is the name of Canada's 1 to 10+ scale for reporting the health risk from air pollution? (Acronym or full name.)
  22. Impacts of Climate Change and How We Respond
    22
    Which of these is an example of adaptation rather than mitigation?
  23. Impacts of Climate Change and How We Respond
    23
    What is the main role of the IPCC?
  24. Impacts of Climate Change and How We Respond
    24
    Which of these is a real effect of climate change on Inuit communities?

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