Climate change and the greenhouse effectIB MYP Physics: Revision notes
Section 1
The greenhouse effect
The Sun's radiation warms the Earth's surface. The warm surface then emits infrared radiation back towards space.
Greenhouse gases in the atmosphere, mainly carbon dioxide, methane and water vapour, absorb this infrared radiation and re-emit it in all directions, including back towards the surface. So less energy escapes to space and the surface stays warmer.
This natural greenhouse effect is essential: without it the average surface temperature would be well below freezing.
Greenhouse gases do not reflect the Sun's light. They absorb infrared radiation from the Earth and re-emit it in all directions.
Section 2
The enhanced greenhouse effect
Human activity has added extra greenhouse gases, so more infrared radiation is trapped. This is the enhanced greenhouse effect.
- Burning fossil fuels for electricity, transport and industry releases carbon dioxide.
- Deforestation removes trees that absorb carbon dioxide, and burning them releases it.
- Cattle farming and rice paddies release methane, and so do rubbish dumps.
The carbon dioxide concentration has risen from about 280 parts per million before industrialisation to over 420 today.
Section 3
Evidence for global warming
Global warming is the rise in the Earth's average surface temperature. Evidence comes from several independent sources:
- thermometer records over more than a century show rising average temperatures
- measurements of carbon dioxide in the air, such as at Mauna Loa in Hawaii, show a steady rise
- air trapped in ice cores shows past carbon dioxide levels and temperatures
- glaciers and ice sheets are shrinking and sea level is rising
The link between carbon dioxide and temperature is a correlation, and scientists support it with the science of how greenhouse gases absorb infrared.
Section 4
Consequences of climate change
- Sea-level rise: land ice melts and adds water to the oceans, and the warmer ocean water expands. Low-lying coasts and islands flood.
- Extreme weather: more heatwaves, droughts, floods and stronger storms.
- Ecosystems: habitats change, so some species cannot cope.
- People: crop failures, water shortages, loss of homes and migration.
Melting floating sea ice does not raise the sea level much, but melting land ice does.
For a six-mark explanation, link each step: more CO₂, more infrared trapped, higher temperature, then melting and expansion, then sea-level rise.
Section 5
Reducing emissions and the link to energy resources
Most carbon dioxide comes from burning fossil fuels, so energy choices matter.
- Replace coal, oil and gas with renewable resources or nuclear power, which release little carbon dioxide when generating.
- Use energy more efficiently, for example LED lighting, better insulation and public transport.
- Stop deforestation and plant trees.
- Reduce methane from farming and waste.
- Governments agree targets together, because climate change is a global problem.
There are trade-offs: renewables cost money to build and can be unreliable, but fossil fuels cause the enhanced greenhouse effect.
Must know
- Greenhouse gases (CO₂, methane, water vapour) absorb and re-emit infrared radiation
- Human activity causes the enhanced greenhouse effect
- Evidence: temperature records, CO₂ measurements, ice cores, melting ice
- Consequences: sea-level rise and extreme weather
- Reduce emissions with renewables, efficiency and trees
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Climate change and the greenhouse effect
- Scientists at a mountain observatory in Hawaii have recorded that the concentration of carbon dioxide in the atmosphere has risen from about 280 parts per million before the Industrial Revolution to over 420 parts per million today.Explain how greenhouse gases help to keep the Earth's surface warmer than it would be without them.2 marks
- Climate scientists in Brazil study how land use changes the atmosphere. In one region, large areas of rainforest have been cleared by burning to create farmland for cattle.Explain why clearing the forest by burning increases the concentration of carbon dioxide in the atmosphere.2 marks
- Students compare how much two clear, sealed bottles warm up when lit by the same lamp for 10 minutes. Bottle A contains air. Bottle B contains air with extra carbon dioxide added. Each bottle starts at 21 °C and the experiment is repeated three times. The temperature rises in bottle A were 3.0 °C, 3.4 °C and 3.2 °C. The temperature rises in bottle B were 5.1 °C, 5.6 °C and 5.3 °C.Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).