Climate Change — Print · Grade 12 Science
Chapter: Pollution, Carbon & Climate EvidenceClimate Change
Learning goals
- I can explain how the greenhouse effect works and identify the main greenhouse gases human activities are adding.
- I can describe several independent lines of evidence that Earth's climate is warming and that humans are the cause.
- I can use the carbon cycle to explain how burning fossil fuels drives climate change.
Readings for this unit
Before this unit
Radiation balance, carbon cycle, and long-term data.
Use the detailed parent plan: two core 50–60-minute sessions per focused unit, with a third assigned for selected calculation/modeling topics. First study the core explanation and Parts 1–2 with their figures/checks; next study Parts 3–4, the whole-unit application, worked cases, varied practice and exit check. Attempt reasoning before opening guidance. Extend time when actual understanding requires it; investigations and chapter assessments have separate sessions.
Start with something to explain
Why is one cold day compatible with long-term warming?
Illustrative evidence case. Short-term regional variation occurs within changing longer-term global statistics.
Notice and wonder
Record two observations using the stated quantities or relationships. Keep observations separate from possible causes. Write one question that a new measurement could help answer.
Why is one cold day compatible with long-term warming?
Your first model
Label region, time interval, baseline and the physical energy boundary.
Build the language from the idea
- greenhouse effect
- The trapping of outgoing heat by atmospheric gases that absorb and re-radiate infrared energy, keeping Earth's surface warmer than it would otherwise be.
- greenhouse gas
- A gas — such as carbon dioxide, methane, water vapor, or nitrous oxide — that absorbs and re-emits the infrared heat radiating from Earth's surface.
- fossil fuel
- A carbon-rich energy source — coal, oil, or natural gas — formed from the buried remains of ancient organisms, storing carbon that had been out of the active cycle for millions of years.
- carbon cycle
- The continuous movement of carbon among the atmosphere, living things, oceans, soil, and rock.
- climate feedback
- A process set off by warming that either amplifies it (a positive feedback, like melting ice) or dampens it (a negative feedback).
The climate system receives solar energy and emits infrared radiation. Greenhouse gases absorb and emit selected infrared wavelengths, affecting how energy escapes to space. Increasing long-lived greenhouse gases changes the radiative balance and leads to an adjustment of temperature and energy storage.
The natural greenhouse effect keeps Earth’s surface substantially warmer than a simplified no-greenhouse radiative model. Human activities add CO₂ through fossil-fuel use and land change and alter other greenhouse gases and aerosols. The ozone-hole mechanism is distinct from this infrared-energy process.
CO₂ values must specify network or location, date, and averaging. For arithmetic this course supplies an illustrative comparison 280ppm to 420ppm;420 is not labeled the current concentration. The modeled increase is 140ppm, or 50% relative to 280. Consult dated observations for real-time values.
Climate attribution combines mechanisms, measured patterns, energy budgets, and comparisons of natural and human influences. A long-term global trend is different from short-term local weather. Independent indicators such as ocean heat, ice change, and temperature records strengthen a coherent explanation.
Effects include changing extremes, sea-level rise through thermal expansion and land-ice loss, and ecosystem shifts; local impacts vary. Ocean acidification is a distinct chemical result of added dissolved CO₂. Feedbacks such as ice-albedo and water-vapor responses can amplify change, while other responses can counteract it.
Projections describe conditional outcomes under stated emissions and land-use assumptions, with physical uncertainty and natural variability. Mitigation reduces drivers; adaptation reduces exposure and vulnerability. Evaluate specific options using their mechanisms, timescale, evidence, costs, and trade-offs.
Model check: The greenhouse effect is not the ozone-hole mechanism; fixed CO₂ examples must have dates or be labeled models.
Build your understanding
Use the detailed parent plan: two core 50–60-minute sessions per focused unit, with a third assigned for selected calculation/modeling topics. First study the core explanation and Parts 1–2 with their figures/checks; next study Parts 3–4, the whole-unit application, worked cases, varied practice and exit check. Attempt reasoning before opening guidance. Extend time when actual understanding requires it; investigations and chapter assessments have separate sessions.
Part 1 · Use an Earth energy balance
An Earth energy balance compares absorbed incoming sunlight with outgoing radiation across the top-of-atmosphere boundary. A positive imbalance increases stored energy, much of it in the ocean. Greenhouse gases absorb and emit selected infrared wavelengths, affecting how surface temperature and outgoing radiation relate. This is not a permanent one-way trap or extra energy source. The balanced 240 W/m² arrows here are illustrative rounded global means, not a current measured imbalance record.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
If absorbed input exceeds outgoing radiation by 1 W/m², what happens to stored energy?
Visual reasoning — after your attempt
It increases at 1 joule per second per square meter while that imbalance persists.
Earth receives mainly shortwave solar energy and emits thermal infrared radiation. Climate depends on the balance and distribution of energy within the system. Greenhouse gases interact with infrared radiation; a changed balance can alter temperatures while oceans and other stores respond over time.
The greenhouse effect is not the ozone hole and does not mean all outgoing radiation is blocked. Separate the physical mechanisms.
Pause and explain
Why is an energy imbalance not identical to an immediate uniform temperature rise?
Check your reasoning after answering
Energy can enter different stores and regions, and response times vary; heat capacity, circulation, and feedbacks affect the pattern.
Part 2 · Distinguish weather variability from climate evidence
Weather describes short-term atmospheric conditions; climate concerns statistical patterns over longer intervals, including means, variation and extremes. A cold season can occur within a long-term warming trend because multiple processes and natural variability operate together. One local event cannot establish or refute a global trend. Use adequate time coverage, a defined region and uncertainty, and keep an illustrative series separate from actual climate observations.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Does one low annual value erase the rest of a longer record?
Visual reasoning — after your attempt
No. Evaluate the full relevant interval and spatial coverage rather than selecting one convenient point.
Weather describes short-term conditions; climate uses statistical patterns over longer intervals. A cold day does not negate a long-term warming trend, and a hot day alone does not establish its cause. Compare consistent records, spatial coverage, and independent indicators.
Temperature, ocean heat, ice, and sea-level records can provide complementary evidence rather than being interchangeable measures.
Pause and explain
Why is one unusual day insufficient to infer a climate trend?
Check your reasoning after answering
Daily variability can be large. A trend needs a sustained, representative time record and an appropriate statistical comparison.
Part 3 · Separate forcing, feedback, and response
A forcing changes the external energy-balance conditions of the chosen system. A feedback is a response pathway that feeds back on the initial change: reduced reflective ice after warming can reinforce additional warming, while increased thermal emission with temperature supplies a stabilizing response. Reinforcing means amplifying, not beneficial; balancing means opposing, not necessarily harmless. Ocean heat capacity and circulation also create delays, so response need not be immediate.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why is “positive feedback” not a value judgment?
Visual reasoning — after your attempt
Positive describes a reinforcing causal loop, not whether the effect is desirable.
A forcing alters the energy balance from outside a defined feedback loop. A feedback responds to a change and can amplify or damp it. Water-vapor and ice-albedo effects involve mechanisms and timescales; positive feedback means amplification, not a beneficial outcome.
Reduced reflective ice can increase absorbed sunlight and support further warming. The loop’s direction must be explained through each link.
Pause and explain
What does positive feedback mean in this context?
Check your reasoning after answering
An initial change produces responses that reinforce that change; positive names the loop direction rather than a value judgment.
Part 4 · Use multiple lines of evidence for attribution
Detection establishes a change relative to a defined variability framework. Attribution evaluates contributing causes using physical mechanisms, observations and comparisons of plausible drivers. Observed modern warming is supported by multiple indicators, while causal assessment also examines greenhouse-gas changes, natural forcing and expected spatial/vertical patterns. One upward temperature curve alone cannot apportion every cause. A projection is conditional on future assumptions and differs from a retrospective attribution statement.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why is correlation between one local series and emissions not a complete attribution study?
Visual reasoning — after your attempt
It lacks the broader mechanisms, alternative drivers, spatial coverage and uncertainty needed to assign causal contributions.
Human influence on recent global warming is supported by physical greenhouse mechanisms and converging observed patterns. Attribution compares explanations, including natural variability and external influences, rather than relying on one correlation. A future scenario adds assumptions about emissions and system response.
An illustrative trend calculation is a mathematical exercise, not the complete evidence for attribution or a precise local forecast.
Pause and explain
Why distinguish a scenario from a measured record?
Check your reasoning after answering
A record summarizes observations; a scenario uses specified future assumptions and models, so its interpretation and uncertainty are different.
Apply the whole unit · Convert a planetary energy imbalance into stored energy
Illustrative constant net imbalance is 0.800 W/m² over a chosen area 1.00×10⁶ m² for one year of 3.15×10⁷ s. Treat this as a supplied energy account, not a measured global value.
Your task
Calculate net power and annual energy gain, explain why those values do not directly determine temperature rise, and identify the quantities needed for a temperature model.
What your response should show
- Define the system, quantities, units, and relevant conditions before selecting a model.
- Show intermediate calculations or a labeled evidence account, including signs or denominators.
- Explain how the supplied evidence supports the conclusion rather than reporting only an answer.
- Identify a meaningful uncertainty, model limit, or measurement needed to test the conclusion.
Response guidance — after your attempt
Net power=0.800×1.00×10⁶=8.00×10⁵ W.
Annual energy gain=8.00×10⁵×3.15×10⁷=2.52×10¹³ J.
A temperature estimate would need the receiving mass, heat capacity, distribution, and relevant transfers or phase changes.
The energy gain follows the stated constant-flux assumption. Temperature cannot be found by treating joules as degrees or ignoring where energy is stored. Actual climate response requires a wider changing account, including transport and feedbacks. The illustrative flux is not a current observational claim.
Scientific references and source-model foundations
Parent / teacher teaching notes
Ask students to distinguish watts per area, total power, accumulated energy, and temperature. Use the primary-source links for observed climate evidence rather than these invented numbers. Ask the learner to explain each symbol, axis, unit and arrow before calculating. Calculated examples, supplied illustrative records and actual historical observations are labeled separately. Selected public OpenSciEd middle-school source figures are foundation examples, not complete high-school editions or an endorsement; all advanced explanations are supplied locally.
An animated diagram of the carbon cycle showing carbon dioxide moving between the atmosphere, plants, animals, and decomposers, with fossil fuel burning adding extra carbon to the atmosphere.
The key idea
Greenhouse gases affect infrared energy balance; use dated climate observations, mechanisms, and alternatives to evaluate change. Supplied CO₂ values are practice comparisons.
Worked examples
Example 1
- Find the increase: 420 ppm - 280 ppm = 140 ppm.
- Divide the increase by the original amount: 140 ÷ 280 = 0.5.
- Convert to a percent: 0.5 × 100 = 50%.
Example 2 · Worked application
- Check whether models reproduce observed magnitude and spatial/time patterns.
- Include multiple potential drivers and uncertainties.
- Converging evidence supports attribution more strongly than one correlation.
Weather fluctuations do not directly establish long-term forcing.
Example 3
- Gasoline is a fossil fuel — carbon that was locked underground, out of the active carbon cycle, for millions of years.
- Burning it combines that carbon with oxygen, releasing carbon dioxide into the atmosphere far faster than photosynthesis and the oceans can remove it.
- The added carbon dioxide is a greenhouse gas, so it absorbs more of Earth's outgoing infrared heat and re-emits some of it back toward the surface.
- With more heat trapped near the surface, the planet's average temperature rises.
Example 4 · Find and fix the mistake
- Test the claim against the stated conditions: Weather fluctuations do not directly establish long-term forcing.
- Regional and short-term variability can occur within a global long-term trend.
Weather fluctuations do not directly establish long-term forcing.
Example 5 · Reason from the visual model
- A forcing changes the external energy-balance conditions of the chosen system. A feedback is a response pathway that feeds back on the initial change: reduced reflective ice after warming can reinforce additional warming, while increased thermal emission with temperature supplies a stabilizing response. Reinforcing means amplifying, not beneficial; balancing means opposing, not necessarily harmless. Ocean heat capacity and circulation also create delays, so response need not be immediate.
- Positive describes a reinforcing causal loop, not whether the effect is desirable.
Original causal-role diagram; it is not a quantified climate sensitivity model.
Avoid these mistakes
- The greenhouse effect is not the ozone-hole mechanism; fixed CO₂ examples must have dates or be labeled models.
Check your understanding
Why does more atmospheric CO₂ affect energy balance?
Discuss the answer
It changes infrared absorption/emission and radiative escape, causing system temperatures to adjust; evaluate multiple observations and forcing mechanisms.
Return to the phenomenon
Return to the initial case. Why is one cold day compatible with long-term warming? Revise your drawing or explanation using two named ideas and one stated limitation.
Compare explanations after your attempt
Weather and climate differ in aggregation; detection and attribution need complete records and mechanisms rather than isolated events.
What should we investigate next?
Which comparison would test a remaining uncertainty? State what you would change, keep comparable and measure.
Investigate, calculate and revise
Keep a first model and an evidence-supported revision. Attempt each task before opening guidance; all required explanations and supplied-data routes are available locally.
Activity 1 · Return to the opening case
Use the opening phenomenon, unit definitions and explained Parts 1–4.
Your task
Return to the initial case. Why is one cold day compatible with long-term warming? Revise your drawing or explanation using two named ideas and one stated limitation.
Success criteria
- Use the stated observations and appropriate units.
- Connect a labeled model with the physical/environmental mechanism.
- State assumptions and an evidence limitation.
- Explain a substantive revision or next test.
Hint
Keep object/material identity, material transfer and energy account distinct.
Response guidance — discuss after your attempt
Weather and climate differ in aggregation; detection and attribution need complete records and mechanisms rather than isolated events.
Activity 2 · Transfer to a changed case
Cover the worked answer and use the explained models, relationships and notebook.
Your task
A model Earth absorbs 242 W/m² and emits 240 W/m² for 10 s. Find stored-energy increase per area and explain why this alone does not give a surface-temperature change.
Success criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the physical or environmental mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.
Hint
Name known quantities and conditions, show intermediate steps and check conservation.
Response guidance — discuss after your attempt
Increase=(242−240)×10=20 J/m². Temperature change also needs heat capacity, depth/distribution of storage and coupled responses; this is a supplied short model interval, not an actual climate measurement.
Words to know
- greenhouse effect
- The trapping of outgoing heat by atmospheric gases that absorb and re-radiate infrared energy, keeping Earth's surface warmer than it would otherwise be.
- greenhouse gas
- A gas — such as carbon dioxide, methane, water vapor, or nitrous oxide — that absorbs and re-emits the infrared heat radiating from Earth's surface.
- fossil fuel
- A carbon-rich energy source — coal, oil, or natural gas — formed from the buried remains of ancient organisms, storing carbon that had been out of the active cycle for millions of years.
- carbon cycle
- The continuous movement of carbon among the atmosphere, living things, oceans, soil, and rock.
- climate feedback
- A process set off by warming that either amplifies it (a positive feedback, like melting ice) or dampens it (a negative feedback).
In the real world
Climate scientists feed decades of geoscience data into global climate models running on supercomputers to forecast how fast the planet will warm under different emission choices — the same heat-trapping physics of CO2 that Svante Arrhenius first calculated by hand in 1896.
Exit check
Why does more atmospheric CO₂ affect energy balance?
Check your explanation after answering
It changes infrared absorption/emission and radiative escape, causing system temperatures to adjust; evaluate multiple observations and forcing mechanisms.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Problem 1
- Argon (Ar)
- Carbon dioxide (CO2)
- Nitrogen (N2)
- Oxygen (O2)
Answer and explanation
Carbon dioxide (CO2)
Carbon dioxide absorbs and re-emits outgoing infrared heat and is released in huge quantities by burning fossil fuels; nitrogen, oxygen, and argon make up most of the atmosphere but do not trap heat this way.
Problem 2
Answer and explanation
50 %
The increase is 420 - 280 = 140 ppm; 140 ÷ 280 = 0.5, or a 50% increase.
Problem 3
- Earth's distance from the Sun is steadily increasing
- The atmosphere is gradually losing its oxygen
- Glaciers and polar ice sheets are shrinking and global sea level is rising
- The number of stars visible at night is steadily decreasing
Answer and explanation
Glaciers and polar ice sheets are shrinking and global sea level is rising
Shrinking ice and rising seas are among many independent measurements — along with the temperature record and ocean warming — that all indicate a warming climate.
Problem 4
Answer and explanation
Fossil fuels store carbon that was locked underground and out of the active carbon cycle for millions of years. Burning them releases that ancient carbon as carbon dioxide in just decades or centuries — far faster than photosynthesis and the oceans can absorb it back — so carbon dioxide builds up in the atmosphere.
Problem 5
Answer and explanation
Weather is the short-term, day-to-day state of the atmosphere, while climate is the long-term average of weather over decades. A single cold day is just weather and doesn't reveal the long-term trend. Climate change is measured by averaging temperature and other data over many years and across the whole globe, which clearly shows warming even though individual cold days still happen.
Problem 6
Hints
Weather fluctuations do not directly establish long-term forcing.
Answer and explanation
Oceans store substantial heat, so air temperature alone does not capture the system's energy change.
Problem 7
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Future emissions, responses and natural variability depend on uncertain choices and processes.
Problem 8
Answer and explanation
Positive describes a reinforcing causal loop, not whether the effect is desirable.
A forcing changes the external energy-balance conditions of the chosen system. A feedback is a response pathway that feeds back on the initial change: reduced reflective ice after warming can reinforce additional warming, while increased thermal emission with temperature supplies a stabilizing response. Reinforcing means amplifying, not beneficial; balancing means opposing, not necessarily harmless. Ocean heat capacity and circulation also create delays, so response need not be immediate.
Positive describes a reinforcing causal loop, not whether the effect is desirable.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the physical or environmental relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 9
Answer and explanation
Increase=(242−240)×10=20 J/m². Temperature change also needs heat capacity, depth/distribution of storage and coupled responses; this is a supplied short model interval, not an actual climate measurement.
Increase=(242−240)×10=20 J/m².
Temperature change also needs heat capacity, depth/distribution of storage and coupled responses; this is a supplied short model interval, not an actual climate measurement.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the physical or environmental mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.