8.4Chapter 8: Weather and Climate

Gathering evidence of climate change — Alhussan Biology - Stage 8 Revision Notes & Topical Questions

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Lesson summary

8.4 Gathering evidence of climate change — Ice Cores, Tree Rings and Bog Pollen — Alhussan International Academy — Biology (Stages 7–9) notes: Describe how scientists gather evidence of modern and past climate change using measurements, fossils, ice cores, tree rings and pollen.C…

Carbon dioxide in the air
Surface temperature
Extreme weather events
Polar ice cover
Peer review
Developing knowledge

Part 1 of 7Investigating modern climate change

1Carbon dioxide in the air

Carbon dioxide in the air it is analysed and is rising every year.

2Surface temperature

Surface temperature it is measured in many places and global temperatures are rising.

3Extreme weather events

Extreme weather events droughts, storms and floods are recorded and are happening more often and more extremely.

4Polar ice cover

Polar ice cover as global temperature rises, more ice melts from land and glaciers, and sea levels rise.

Part 2 of 7Peer review and sharing knowledge

1Peer review

Peer review checking of a scientist's work by other scientists before it is published in a scientific journal.

It makes sure the work is reliable and the experiment can be repeated.

2Sharing

Sharing scientists share discoveries and methods worldwide, so everyone gains and understanding moves forward.

3Developing knowledge

Developing knowledge scientific knowledge grows as scientists work together and build understanding over time.

Part 3 of 7Why indirect evidence is needed

Records

Records thermometers and weather records go back only about 150 to 200 years.

Proxy evidence

Proxy evidence natural records in which the climate left a trace.

Evidence must be dated and compared from several sources to be trusted.

Graphs of natural climate cycles over thousands of years are built from evidence from many sources.

Part 4 of 7Fossils

Fossils

Fossils the remains of animals and plants from millions of years ago.

Climate clue

Climate clue the type of fossil found in an area shows the climate there when the organisms were alive.
Fossil shells on a cold UK beach came from animals that needed a warm, Mediterranean climate, which shows change over 35 million years.

Part 5 of 7Ice cores

Formation

Formation in Antarctica and Greenland each year's snow is compressed by later snowfall into layers of ice, so the oldest ice is at the bottom.

Cores

Cores scientists drill cylinders of ice, some more than 3 km long and covering up to 800 000 years.

Trapped air

Trapped air tiny bubbles hold ancient air, which is analysed for carbon dioxide, methane and the mixture of gases in the past atmosphere.

Temperature

Temperature oxygen isotopes in the ice reveal the temperature when the snow fell.

Findings

Findings carbon dioxide and temperature have risen and fallen together, and current carbon dioxide is higher than at any time in the record.

Part 6 of 7Tree rings

Growth

Growth a tree grows a new ring of wood each year.
A warm, wet year gives a wide ring, and a cold or dry year gives a narrow ring.

Use

Use counting rings gives the age of the tree, and measuring widths gives the climate year by year.

Longer records

Longer records long-lived trees and old timber from buildings extend the record back thousands of years.

Limitations

Limitations rings show only local conditions and the life of the tree, and growth is also affected by disease and competition.

Part 7 of 7Pollen in bogs and ice

Preservation

Preservation pollen grains have tough coats that survive for thousands of years in waterlogged, acidic peat bogs where oxygen is too low for decomposers,
- and also in ice.

Dating

Dating peat builds up in layers, so deeper layers are older.

Method

Method a core is taken and the pollen in each layer is identified under a microscope, because each plant species makes pollen of a different shape.

Interpretation

Interpretation pollen of cold-loving plants such as birch and pine suggests a cool period, and oak and hazel suggest warmer conditions.

Evidence	What it shows	Limitation
Ice core	Temperature and greenhouse gases	Only polar regions
Tree rings	Yearly growth, warm or cold, wet or dry	Limited age; local
Bog pollen	Plant types, so temperature and rainfall	Dating can be uncertain

Key terms

Term	Meaning
Proxy evidence	A natural record in which past climate left a trace.
Ice core	A cylinder of ice drilled from a polar ice sheet.
Peer review	Checking of scientific work by other scientists before publication.
Fossil	The preserved remains of an organism from long ago.
Pollen	Grains made by plants, each type with a different shape.
Peat	Partly decayed plant material that builds up in waterlogged bogs.

Avoid these mistakes

Saying tree rings measure temperature only — water and nutrients also affect growth.

Forgetting that the oldest ice is at the bottom of the core.

Believing pollen is preserved in all soils — it needs waterlogged, oxygen-poor conditions.

Saying evidence from one ice core proves global changes.

Last updated: 18 October 2026