12.5Chapter 12: The Carbon Cycle and Climate Change
Evaluating evidence for climate change — Alhussan Biology - Stage 9 Revision Notes & Topical Questions
5 min read 8 parts Lesson 5 of 6 1 quiz
Lesson summary
12.5 Evaluating evidence for climate change — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the types of evidence for climate change and judge their quality by considering source, method, sample and bias.IPCC view — the IPCC is convinced that rising atmosp…
- Direct measurements
- Proxy records
- Biological evidence
- Tree rings
- Peat bog cores
- Putting evidence together
Section 1 of 8Types of evidence
Types of evidence
IPCC view
- IPCC view the IPCC is convinced that rising atmospheric carbon dioxide from human activities is causing global warming and climate change.
Direct measurements
- Direct measurements thermometer records from weather stations over 150 years, ocean temperatures, and satellite data on ice cover and sea level.
Proxy records
- Proxy records ice cores, tree rings and pollen show earlier climates.
Biological evidence
- Biological evidence plants flower earlier in spring and species move towards the poles or up mountains.
- For example the Jersey tiger moth is spreading north in the UK as temperatures rise.
Section 2 of 8Mauna Loa Observatory
Site
- Site it sits high on a volcano in Hawai'i, where the air is clean and there is little human activity or plant life.
Data
- Data scientists have collected data on the composition of the air there since the 1950s.
Finding
- Finding carbon dioxide concentration in the atmosphere is rising every year.
Section 3 of 8Looking back in time
1Ice cores
- Ice cores cores of ice from the Antarctic build up in layers, and the bubbles of trapped air are thousands of years old.
- Analysing the gas gives carbon dioxide concentrations up to thousands of years ago.
- The deepest layers are the oldest.
2Tree rings
- Tree rings each ring represents a year of growth, and rings are wider in warm, wet years than in cooler, drier years.
- Counting the rings gives the age of the tree.
- Some trees live for hundreds or thousands of years, so tree-ring evidence is combined with ice cores.
3Peat bog cores
- Peat bog cores the plants that formed peat grew thousands of years ago, and cores give a record up to 12 000 years back.
- Pollen is preserved in the peat and shows which plants grew at different times.
4Putting evidence together
- Putting evidence together scientists combine sources to reconstruct atmosphere and temperature over time, identify trends and link them to causes.
- Combining sources increases validity.
- The evidence is very strong that carbon dioxide is increasing and causing warming, and strong that the rise results from human activity.
Section 4 of 8Questions to ask about evidence
Source
- Source who produced it, and is it a research organisation, a university or a company with an interest in the result?
Method
- Method how was the data collected, were the instruments accurate and was the sample large and representative?
Peer review
- Peer review was the work checked by other experts?
Agreement
- Agreement do other independent studies give the same result?
Logic
- Logic do the conclusions follow from the data, or are they exaggerated?
Section 5 of 8Common errors in interpreting data
1Cherry-picking
- Cherry-picking choosing a short period that fits a view, such as one cold winter, instead of the long-term trend.
2Weather and climate
- Weather and climate confusing the two.
3Correlation without cause
- Correlation without cause two graphs may both rise without one causing the other.
- The carbon dioxide and temperature link is supported by physics (infrared absorption) as well as by correlation.
4Poor graphs
- Poor graphs a truncated axis can make small changes look large.
Section 6 of 8Weighing the case
Temperature record
- Temperature record the global average has risen about 1.1 °C since 1880 even though individual years rise and fall.
- The rise matches the increase in carbon dioxide from human sources and fits predictions based on the greenhouse effect.
- Natural factors such as solar output and volcanoes cannot explain the recent warming.
Uncertainty
- Uncertainty scientists give ranges for future warming because the outcome depends on future emissions and feedbacks such as melting ice.
Balanced conclusion
- Balanced conclusion evidence from many independent sources strongly shows the Earth is warming with human activity the main cause,
- while details remain uncertain.
| Stronger evidence | Weaker evidence |
|---|---|
| Long-term data from many places | Data from one place or a few years |
| Peer-reviewed, repeated by others | Unpublished or from an interested group |
| Methods explained, with uncertainty given | Claims without methods |
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Proxy evidence | A natural record of past climate. |
| Cherry-picking | Choosing only data that fit a view. |
| Peer review | Checking of scientific work by other experts. |
| Validity | How well the evidence supports the conclusion. |
| Mauna Loa Observatory | A site in Hawai'i recording atmospheric carbon dioxide since the 1950s. |
| Correlation | A relationship between two variables. |
Section 8 of 8Exam technique
1
Accepting a claim because it appears on a website.
2
Believing uncertainty means the science is wrong.
3
Using only one period of data.
4
Forgetting to check who funded the research.
Marked practiceQuizzes for this lesson
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