What you need to know
- 5.16Recognising correlations and causal relationships in climate evidence.
- 5.25Conclusions on controversial issues can depend on who is reaching them.
This is a scientific-method lesson, not a party-political script. Named organisations appear as examples of interest, not as villains or saints. Greenhouse physics remains 5C 4.
By the end, you should be able to…
- Define correlationA relationship in which two variables change together. A correlation does not prove that one causes the other. and contrast it with a causal mechanism.
- Use greenhouse physics as the proposed causal link between CO₂ and warming.
- Explain why the source of a conclusion about climate action matters.
Build your understanding
Together, then because
A correlationA relationship in which two variables change together. A correlation does not prove that one causes the other. means two variables change together: CO₂ concentration and global mean temperature have both risen in the instrumental period. Ice-core series also show CO₂ and Antarctic temperature moving together across glacial cycles. Correlation is not yet “CO₂ caused the warming”. A third factor could drive both, or the arrow could run partly the other way: warmer oceans release CO₂.
A causal claim needs a mechanism. greenhouse gasA gas, such as CO₂ or methane, that absorbs infrared radiation in the atmosphere. absorb long-wave infrared. That physics, plus the size of the human carbon transfer from 5C 3, is why scientists treat rising fossil-fuel CO₂ as a cause of recent warming, not a coincidence. You still have to say that, not just point at two rising lines.
What would weaken a causal story
If warming had led and CO₂ had not risen, the simple greenhouse account of this century would be in trouble. If a proposed alternative (solar output, orbital cycles) matched the last 150 years better than greenhouse forcing, you would have to weigh it. Orbital Milankovitch cycles matter on ice-age timescales; they are a poor explanation of the post-1950 spike. Evaluate the alternative; do not ignore it.
Local weather is noisy. A cold February in one city is not a disproof, and a record summer is not, by itself, a proof. Causal evaluation uses long records, many sites, and a mechanism.
Who is reaching the conclusion
Specification 5.25 says conclusions about how much humans affect climate, or what actions to take, can depend on who is speaking. A company whose assets are fossil reserves has an interest in delaying cuts. A renewable manufacturer has an interest in subsidies. A government may protect jobs in one region. An IPCC assessment has a different process: many authors, open review, governments approving a summary. None of that replaces data — it tells you to ask who paid, what was omitted, and whether methods were public.
“Scientists disagree” can be true at the margin (how fast, which policy) and still false as a claim that there is no greenhouse mechanism. Read the actual question: degree of human influence, or choice of action, are the controversial parts 5.25 names.
NOT: two graphs that rise together do not, by themselves, prove the named gas caused the change.
- Warmer oceans can also release CO₂, so the arrow is not only one way in ice cores
- A cold week in one city is weather, not a disproof
- Ask who is reaching a conclusion about policy or the size of the human effect
- Disagreement about actions is not disagreement that the mechanism exists
- Milankovitch cycles are the orbital alternative named for ice-age timing
Two traps this diagram blocks
- Do not treat correlation as cause without a mechanism.
- Do not use one week of weather as the whole test.
From the diagram alone
Question
Explain why a graph of rising CO₂ and rising temperature is not, on its own, a complete causal argument. [3]
Show a model answer
The graph shows a correlation. A cause needs a mechanism, here the absorption of long-wave infrared by greenhouse gases. Another driver, or a reverse effect such as warmer oceans releasing CO₂, has to be considered before the gas is accepted as the cause.
| Claim type | What you still need | A weak version |
|---|---|---|
| Correlation | Two measured series that track | Two doodled lines with no source |
| Causal | Mechanism (greenhouse absorption) plus timing and size | “They both went up so it must be CO₂” with no physics |
| Action / policy | Who benefits, what was left out, quality of the data | Accepting a blog or a company advert as equivalent to an assessed report |
Make your reasoning visible
Borrow 1C language
correlationA relationship in which two variables change together. A correlation does not prove that one causes the other. is not cause — you already practised this on CVD risk.
Name an interest without smearing
“This report was funded by X, so check omissions” is specification-level. Abuse is not.
Key explanations
- The mechanism is that greenhouse gasA gas, such as CO₂ or methane, that absorbs infrared radiation in the atmosphere. absorb long-wave infrared, and human activity has increased those gases.
- A warmer ocean releasing CO₂ is a reason to check the direction of the arrow, especially on long ice-core records.
- One local weather event is too short to confirm or reject the long-term claim.
Avoid this misconception
The claim: If two graphs rise together, the first named gas caused the climate change.
The correction: That is a correlation. Cause still needs a mechanism and a check that other drivers do not fit better.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
CO₂ and temperature have both risen. Why is that not, by itself, proof of cause?
Show suggested answer
They are correlated. A causal claim needs a mechanism (greenhouse absorption of infrared) and consideration of other drivers.
Practice question
Retrieval and explanation · suggested answer
State the mechanism that links extra CO₂ to warming.
Show suggested answer
CO₂ is a greenhouse gas: it absorbs outgoing long-wave infrared, so extra CO₂ enhances the greenhouse effect.
Practice question
Retrieval and explanation · suggested answer
Give one reason a conclusion about climate action might depend on who reaches it.
Show suggested answer
The author may have financial, political or campaign interests that affect which options they emphasise or omit (for example a fossil-fuel producer versus an assessed scientific panel).
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Ice cores show CO₂ falling as ice ages deepen. A student says that proves temperature causes CO₂, so fossil fuels cannot cause warming. Untangle the two timescales.
Show a hint
Both directions can exist; they do not cancel 5.17.
Explore the reasoning
On ice-age timescales, orbital warming can outgas CO₂ from oceans, a feedback. That does not stop extra fossil CO₂ absorbing infrared now. Two causal arrows can exist. The industrial rise in CO₂ is too large and fast to be explained as a passive response to a small temperature wiggle.
Recall this lesson
Lesson recall questions
Question 1 of 5: How can pollen in a peat bog be used as evidence of past climate?
Evidence for climate change
Practice question
Retrieval and explanation · suggested answer
How can pollen in a peat bog be used as evidence of past climate?
Lesson: 5C 5: Looking at the Evidence
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Process is part of the evidence
5C · The Global Warming Debate: Correlation or Causation?The IPCC describes itself as assessing published science through many authors and rounds of review, with governments then approving a summary line by line. That process does not…Specification 5.25Read & use the scienceClose article
Why this matters
The IPCC describes itself as assessing published science through many authors and rounds of review, with governments then approving a summary line by line. That process does not make every sentence perfect. It is different from a single-interest press release. 5.25 asks you to notice the difference, not to memorise the panel’s organogram. Authors assess a body of published evidence and state confidence and uncertainty. This makes an assessment different from a laboratory measurement: conclusions are reasoned from many studies, not simply read from one instrument.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.25 understand the way in which scientific conclusions about controversial issues, such as what actions should be taken to reduce climate change, or the degree to which humans are affecting climate change, can sometimes depend on who is reaching the conclusions
Use the science
Why is “the IPCC is a UN body” not a sufficient reason to discard its physical chapter?
Explore a possible response
Institutional home is an interest to note; you still have to engage the measurements and mechanisms. Source criticism is not the same as refusing the data.
Explore the source
Who checks an assessment report?
5C · The Global Warming Debate: Correlation or Causation?The IPCC publishes drafts for expert and government review, and authors respond to comments before a report is finalised. Review editors check that comments are considered. This does…Specification 5.25Read & use the scienceClose article
Why this matters
The IPCC publishes drafts for expert and government review, and authors respond to comments before a report is finalised. Review editors check that comments are considered. This does not make every conclusion infallible, but it means the work is more than one person’s opinion or a viral screenshot of a graph. A science-policy analyst reads the evidence, confidence language and stated assumptions before recommending action. The same habit helps students distinguish a disagreement about measurements from a disagreement about costs or priorities. One can question a conclusion without pretending that the review process or the underlying observations do not exist.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.25 understand the way in which scientific conclusions about controversial issues, such as what actions should be taken to reduce climate change, or the degree to which humans are affecting climate change, can sometimes depend on who is reaching the conclusions
Use the science
A headline quotes one IPCC sentence. What should you inspect before deciding whether it supports a proposed policy?
Explore a possible response
Check the full claim, evidence, confidence, assumptions and whether the policy conclusion follows from the assessed science or adds value judgements.