Biology & life sciences · 11 / 12
Earth and climate: stocks, flows, evidence
Final-year concepts · Worked example and 4 exercises with solutions, at your pace.
The principle, simply
A reservoir holds an amount; a flow transfers matter or energy per unit time. The carbon cycle connects air, oceans, organisms and rocks. Interpret climate evidence by identifying period, indicator and mechanism; local observations differ from global trends. Independent evidence strengthens an explanation.
- 01Reservoirs
- 02Flows
- 03Period balance
- 04Evidence and scale
WORKED EXAMPLE
From principle to reasoning
A forest takes up carbon through photosynthesis and releases it through respiration and decomposition. Its stock increases when inputs exceed outputs over the period.
Solve a problem in this subject
- Frame a question
State the relationship to explain and its scale: molecule, cell, organism, population or geological time.
- Describe evidence
Give a measurable observation, unit, comparison and conditions before explaining it. Observation and inference do different jobs.
- Connect a mechanism
Use a precise concept and label arrows as production, transfer, action or transformation. Sequence alone does not prove causation.
- Answer with a limit
Connect evidence and knowledge to the question. Distinguish the simplified model from living systems and identify a missing condition.
YOUR TURN
01 · Try before checking
Why does one cold day not refute a climate trend?
One hint
Compare time and spatial scales.
Reveal and understand the solution
Weather describes short-term conditions; climate concerns distributions and trends across long periods. An isolated observation cannot describe the global distribution.
Compare method, conditions and answer; identify the exact part to revisit.
IMPROVE THROUGH PRACTICE
Three additional challenges with solutions
Start with the first challenge. Write your method before opening a hint; use the solution to find the first step that needs work.
Why does one cold day not refute decades of climate change?
A hint to get started
Compare time and spatial scales.
Step-by-step solution
- Weather describes short-term local conditions.
- Climate uses distributions and trends over long periods.
- One observation cannot overturn a global long-term trend.
Which step did you miss? Retry without help, then explain why the method works.
Melting replaces a bright surface with dark ground. What happens to absorbed sunlight?
A hint to get started
The bright surface reflects more.
Step-by-step solution
- Albedo decreases.
- More incoming radiation is absorbed.
- This can amplify warming: a positive feedback in this mechanism.
Which step did you miss? Retry without help, then explain why the method works.
Temperature and CO₂ series covary. How can reasoning go beyond correlation?
A hint to get started
Add mechanisms and independent observations.
Step-by-step solution
- First describe covariation and uncertainty.
- Examine physical mechanisms, possible causes and independent data.
- Correlation alone does not prove causation; converging evidence can support an explanation.
Which step did you miss? Retry without help, then explain why the method works.
The trap to avoid
Do not confuse stocks and flows or correlation with an established mechanism.
Without notes, can you…
- Explain the principle in your own words?
- Rebuild the diagram and its connections?
- Solve the exercise and justify the method?
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