Climate Change — Practice · Grade 12 Science

Chapter: Pollution, Carbon & Climate Evidence

What this practice covers

By the end of Climate Change you should be able to:

9 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: greenhouse effect, greenhouse gas, fossil fuel, carbon cycle, climate feedback.

Problem 1

Which of these gases is a major greenhouse gas that human activities are adding to the atmosphere?
  1. Argon (Ar)
  2. Carbon dioxide (CO2)
  3. Nitrogen (N2)
  4. 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

Using the supplied comparison 280ppm to 420ppm, Atmospheric carbon dioxide has risen from about 280 ppm before the Industrial Revolution to about 420 ppm in this supplied model. By what percentage has it increased?
Answer and explanation

50 %

The increase is 420 - 280 = 140 ppm; 140 ÷ 280 = 0.5, or a 50% increase.

Problem 3

Which of the following is a line of evidence that Earth's climate is warming?
  1. Earth's distance from the Sun is steadily increasing
  2. The atmosphere is gradually losing its oxygen
  3. Glaciers and polar ice sheets are shrinking and global sea level is rising
  4. 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

Explain why burning coal, oil, and natural gas adds carbon dioxide to the atmosphere faster than the natural carbon cycle can remove it.
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

A friend points to one record-cold day and says it proves global warming isn't real. Using the difference between weather and climate, explain what is wrong with that argument.
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

Why include oceans as well as air temperatures in climate-energy accounting? Show the reasoning, not just the conclusion.
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

Why are scenario projections conditional rather than exact predictions?
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

Separate an initiating forcing from a feedback responseSeparate an initiating forcing from a feedback responseExternal forcingChanged energy balanceTemperatureresponseStorage / delayedadjustmentFeedbackAmplifies or opposesresponseForcing, feedback and response are causal roles, not synonyms.Example feedback: warming → ice loss → less reflection → warming.
Original causal-role diagram; it is not a quantified climate sensitivity model.
Interpret the supplied visual. Why is “positive feedback” not a value judgment?
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

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.
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.

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