4.11.1Theme D — Continuity and change
Causes of Climate Change — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 13 of 14 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4The Greenhouse Effect
Short-wave radiation from the Sun warms the surface, which then radiates longer-wavelength heat back towards space.
Natural effect
- Natural effect Gases such as carbon dioxide and methane absorb heat radiated from Earth's surface and re-emit it, keeping the planet warm enough for life.
Greenhouse gas
- Greenhouse gas Any gas in the atmosphere that absorbs infrared radiation from the surface and so reduces heat lost to space.
Enhanced effect
- Enhanced effect Human activities have raised carbon dioxide and methane concentrations, strengthening the effect and causing global warming.
Terminology
- Terminology The greenhouse effect is natural;
- global warming is the rise in temperature;
- climate change is the wider long-term shift in weather patterns.
| Gas | Main human sources |
|---|---|
| Carbon dioxide | Burning fossil fuels, deforestation, peat harvesting, soil degradation |
| Methane | Cattle farming, rice paddies, landfill, fossil fuel extraction |
Part 2 of 4Evidence and Correlation
Scientists use patterns in data and an understanding of mechanisms to judge how strongly evidence supports a conclusion.
Evidence and Correlation
Rising concentrations
- Rising concentrations Carbon dioxide and methane have increased steeply since the industrial revolution, when fossil fuel use began to rise.
Ice cores
- Ice cores Air trapped in Antarctic ice shows that temperature and carbon dioxide rose and fell together over hundreds of thousands of years.
Positive correlation
- Positive correlation As one variable increases the other also increases;
- a negative correlation is when one rises as the other falls.
Correlation versus causation
- Correlation versus causation A correlation alone does not prove one variable causes the other;
- mechanisms and other evidence are also needed.
Part 3 of 4Positive Feedback Cycles
Positive feedback amplifies a change and moves a system further from its starting state.
1
Warming melts polar ice and snow, which are light-coloured and reflective, exposing darker land and sea that absorb more heat.
2
Higher temperatures speed up the enzyme-controlled decomposition of organic matter, so decay organisms release more carbon dioxide.
3
Thawing permafrost releases trapped carbon dioxide and methane, the latter produced by methanogenic archaea.
4
Warmer, drier conditions bring more droughts and wildfires, which release carbon dioxide and remove photosynthesising plants.
5
Each effect adds more greenhouse gas or absorbed heat, causing further warming and driving the system towards a tipping point.
Part 4 of 4Exam Checklist & Tips
4.11.1 – Key Points for the Exam
- Greenhouse gas A gas that absorbs infrared radiation emitted by Earth and so warms the atmosphere.
- Albedo The fraction of incoming light that a surface reflects.
- Permafrost Ground that remains frozen throughout the year.
- Positive feedback A process in which a change causes further change in the same direction.
- Anthropogenic Caused by human activity.
Common Mistakes
- Using greenhouse effect and global warming as if they mean the same thing.
- Saying that correlation proves causation in the carbon dioxide and temperature data.
- Calling methane a form of carbon dioxide; it is a separate gas, CH₄.
- Describing positive feedback as a good outcome; it means amplification, not benefit.
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