What you need to know
- 5.16Records of carbon dioxide levels and pollen in peat bogA waterlogged habitat where dead plants decompose very slowly, so their carbon is stored as peat. as climate evidence.
Ice-core chemistry beyond “trapped air” is enrichment. Required 5.16 names remain CO₂ records, temperature records, pollen in peat and dendrochronology.
By the end, you should be able to…
- Explain how bubbles in ice extend the CO₂ record beyond Mauna Loa.
- Keep pollen as a vegetation proxy, not a gas analyser.
- Separate method from extra named isotopes you need not learn.
Build your understanding
Air from before flasks
Direct CO₂ analysers at Mauna Loa start in 1958. Ice sheets trap bubbles of old air as snow densifies. Measuring those bubbles extends the carbon-dioxide record through glacial cycles. NOAA’s paleoclimatology archive treats ice cores alongside tree rings and sediments as proxy and trapped-gas records. You are not expected to name every Antarctic core.
The method still has limits: dating the ice, whether the bubble matches the exact year of the snow, and laboratory contamination. It is a CO₂ record, which 5.16 already asked for, not a fifth unspecified technique.
Peat as a different archive
Peat stores organic matter, including pollen, under waterlogged, often acidic conditions that slow decay. That is why 5.16 names pollen in peat bogA waterlogged habitat where dead plants decompose very slowly, so their carbon is stored as peat. rather than “any old mud”. The carbon locked in peat is also a store in the 5.18 cycle — draining and burning peat is both a habitatThe place where an organism lives. loss and a CO₂ source. The Thinking Bigger point is that one landscape can be an evidence archive and a carbon store.
Do not treat a peat pollen diagram as a Keeling curve. One is plant communityAll the populations of different species living in one habitat at the same time. through depth; the other is gas concentration through time. They can be dated onto a shared axis; they still measure different things.
Make your reasoning visible
Trapped air versus proxy
Ice-core CO₂ is still a gas measurement. Pollen is a biological stand-in for climate.
Do not inflate the syllabus
Extra isotope names from a research paper are not automatic 5.16 content.
Avoid this misconception
The claim: Ice cores measure temperature because ice is cold.
The correction: Bubbles hold gases. Temperature is reconstructed from other properties or from other records. Cold ice is the storage medium, not the thermometer reading.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Why can ice cores extend a CO₂ record that flasks cannot?
Show suggested answer
They trap ancient air bubbles, so concentration can be measured for times before continuous instrumental sampling.
Practice question
Retrieval and explanation · suggested answer
Why is peat specified, not any soil, for pollen evidence?
Show suggested answer
Waterlogged, often acidic peat preserves pollen by slowing decomposition.
Practice question
Retrieval and explanation · suggested answer
Which 5.16 methods are still required after this page?
Show suggested answer
CO₂ records, temperature records, pollen in peat bogs, and dendrochronology.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A student argues that because ice cores contain CO₂, pollen is redundant. Defend keeping both in 5.16.
Show a hint
Gas versus community.
Explore the reasoning
CO₂ is one greenhouse gas. Pollen shows how plant communities — and therefore local climate and seasons — actually changed. A gas record without ecological response, or a pollen record without a greenhouse mechanism, is incomplete. They answer different parts of “climate change and its causes”.
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.
The world’s climate lumber room
5C · Thinking BiggerNOAA NCEI’s paleoclimatology programme archives ice cores, tree rings, corals and sediments so that natural climate variability can be compared with the instrumental era. That institutional archive is…Specification 5.16Read & use the scienceClose article
Why this matters
NOAA NCEI’s paleoclimatology programme archives ice cores, tree rings, corals and sediments so that natural climate variability can be compared with the instrumental era. That institutional archive is why 5.16 can name several independent methods. Their files are not a school graph to copy. Each archive has a different time resolution and a different biological or physical proxy. Independent signals can be compared, but they should not be treated as identical direct measurements of air temperature.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.16 understand the different types of evidence for climate change and its causes, including records of carbon dioxide levels, temperature records, pollen in peat bogs and dendrochronology, recognising correlations and causal relationships
Use the science
Why store both ice-core gas and tree rings if both “show climate”?
Explore a possible response
They measure different variables (air composition versus growth). Agreement between independent methods is stronger than one archive alone.
Explore the source
- NOAA NCEI: paleoclimatologyNOAA NCEI
Air trapped in ancient ice
5C · Looking at the EvidenceNOAA explains that bubbles in ice cores preserve samples of past atmosphere, while properties of the surrounding ice record other environmental information. This gives a different kind of…Specification 5.16Read & use the scienceClose article
Why this matters
NOAA explains that bubbles in ice cores preserve samples of past atmosphere, while properties of the surrounding ice record other environmental information. This gives a different kind of evidence from tree rings or pollen in a peat bog. A paleoclimatologist compares archives because each proxy measures something different and covers different times and places. Past carbon dioxide and temperature can be correlated, but correlation alone does not identify every causal pathway. Physical knowledge of greenhouse gases and independent observations strengthen the interpretation. Ice is therefore an archive to analyse, not a perfect thermometer or a single decisive graph.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.16 understand the different types of evidence for climate change and its causes, including records of carbon dioxide levels, temperature records, pollen in peat bogs and dendrochronology, recognising correlations and causal relationships
Use the science
Why is comparing ice-core gas with temperature proxies stronger than reading only one ice-core variable?
Explore a possible response
They are partly independent measurements. Agreement can support a pattern, while differences reveal uncertainty or other influences.
Explore the source
- How can ice teach us about climate?NOAA NCEI