Evidence for Change
How we know the climate has changed over time, from ice cores and tree rings to written records, and the natural and human causes behind the change.
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How do we know it changed?
The climate has shifted many times over the long history of the Earth, long before anyone kept records. So how can scientists tell what past climates were like, and what has driven the changes? This module looks at the evidence for climate change and at the natural and human causes behind it.
Evidence words to know
Learn these before you sort the evidence and causes.
Natural against human
Climate change has both kinds of cause.
Name the evidence, split the cause
In the exam, name a specific type of evidence rather than saying scientists say so. An ice core or a set of tree rings is a real, datable source. When you explain a cause, decide clearly whether it is natural, from the planet itself, or human, from what people do. Keep the two kinds of cause in separate sentences.
Match the evidence
- ice cores
- tree rings
- written records
- preserved pollen
- trap old air deep in their layers
- show a wider band in a good year
- diaries and harvest logs from the past
- shows which plants grew long ago
Natural or human cause?
- a change in the orbit of the Earth
- a large volcanic eruption
- burning coal, oil and gas
- clearing large areas of forest
- a natural cause from the planet
- a natural cause that dims sunlight
- a human cause adding greenhouse gases
- a human cause removing carbon stores
Why use an ice core?
Why is an ice core useful evidence for past climate?
- Its layers trap bubbles of old air that show what the atmosphere was like.
- Scientists simply guess from how cold it feels.
- Because ice never changes at all.
- Because it grows one ring each year.
Spot the human causes
Select the TWO human causes of climate change.
- Burning coal, oil and gas for energy
- Clearing forests for farmland
- A slow change in the orbit of the Earth
- A change in the output of the Sun
Read the ice-core layers
An ice core forms one layer a year. The top layer is labelled year 100 and a deeper layer is labelled year 60. Subtract to find how many years of climate history lie between them. What is the answer?
Order the ice-core method
Put the steps of using an ice core in order, earliest first.
- Drill out a core of ice
- Count the yearly layers
- Test the trapped air
- Work out the past climate
Complete the facts
Scientists read past climates from evidence such as _____ cores and tree _____. A change in the orbit of the Earth is a _____ cause, while burning coal, oil and gas is a _____ cause.
Spot the natural causes
Tap the TWO natural causes of climate change.
- volcanic eruptions
- changes in the Sun
- exhaust from traffic
- gases from factories
Classify it
Read each item and choose the best label.
- A team drills deep ice and tests the air trapped in its layers. What are they using?
- A huge volcanic eruption throws dust high into the air and cools the planet for a time. What is this?
- A country burns huge amounts of coal, adding greenhouse gases to the air. What is this?
Explain the evidence and causes
Explain how scientists know the climate has changed and describe both a natural and a human cause of that change.
- Name two types of evidence and say what each one shows
- Describe one natural cause of climate change
- Describe one human cause of climate change