BIOLOGY · Stage 9 · Chapter 12: The Carbon Cycle and Climate Change
Biology 12.5 Evaluating evidence for climate change
5 min read 6 parts Lesson 5 of 6
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 6Types of evidence
- IPCC view
- the IPCC is convinced that rising atmospheric carbon dioxide from human activities is causing global warming and climate change.
- Direct measurements
- thermometer records from weather stations over 150 years, ocean temperatures, and satellite data on ice cover and sea level.
- Proxy records
- ice cores, tree rings and pollen show earlier climates.
- 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 6Mauna Loa Observatory
- 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
- scientists have collected data on the composition of the air there since the 1950s.
- Finding
- carbon dioxide concentration in the atmosphere is rising every year.
Section 3 of 6Looking back in time
1Ice cores3 points
- 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 rings3 points
- 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 cores2 points
- 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 together3 points
- 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 6Questions to ask about evidence
- Source
- who produced it, and is it a research organisation, a university or a company with an interest in the result?
- Method
- how was the data collected, were the instruments accurate and was the sample large and representative?
- Peer review
- was the work checked by other experts?
- Agreement
- do other independent studies give the same result?
- Logic
- do the conclusions follow from the data, or are they exaggerated?
Section 5 of 6Common errors in interpreting data
- Cherry-picking
- choosing a short period that fits a view, such as one cold winter, instead of the long-term trend.
- Weather and climate
- confusing the two.
- 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.
- Poor graphs
- a truncated axis can make small changes look large.
Section 6 of 6Weighing the case
- 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
- scientists give ranges for future warming because the outcome depends on future emissions and feedbacks such as melting ice.
- 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 |
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