Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 820–833 of the course textbook. Image credits are on slide 13.
Human activity has raised atmospheric carbon dioxide, mainly through burning fossil fuels and deforestation, and methane, for example from ruminants, rice fields and landfill. These gases absorb long-wave radiation and warm the atmosphere.
In a positive feedback, warming causes changes that lead to more warming. Examples are carbon dioxide released from the deep ocean, more solar radiation absorbed as snow and ice are lost, faster decomposition in thawing permafrost, and more droughts and forest fires.
Watch out: positive does not mean good. It means the effect increases the original change.
Warmer temperatures and less winter snow bring more drought, and primary production falls in the taiga. Forests turn brown and die back, so they may change from accumulating carbon to losing it.
Early break-up of Antarctic landfast ice threatens the breeding grounds of emperor penguins. Loss of Arctic sea ice removes the resting places of Pacific walruses.
Warmer surface water can prevent upwelling of nutrients. This changes its timing and extent, reducing primary production in the ocean and the flow of energy through marine food chains.
Species are moving upslope and towards the poles. On two mountains in Papua New Guinea, the upper limits of bird species moved up by about 110 to 150 m between the 1960s and 2012–13. Ranges of tree species in North America are contracting in the south and spreading north.
More dissolved carbon dioxide causes ocean acidification, which suppresses calcification. Warmer water causes bleaching, as corals expel their algae. Reefs cover less than 0.1% of the ocean yet hold about a quarter of marine species, so their loss could cause the ecosystem to collapse.
Approaches include afforestation, forest regeneration and restoring peat-forming wetlands. Hinewai Reserve in New Zealand is an example of rapid regeneration after degradation. Use a local peatland as a second example.
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Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all eight statements, from quick recall to data questions and a longer answer. It has 36 marks and takes about 35 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
Questions built on realistic experimental data, in the style of Paper 1B and Paper 2. Work them on paper and show your working. 13 marks in total. Your teacher has the mark scheme.
White syndrome is an infectious disease that kills coral tissue. Over six years, scientists surveyed reefs on the Great Barrier Reef. Each summer they counted the number of weeks in which the sea was at least 1 °C warmer than normal ("warm weeks"), and the number of new cases of disease per 1000 coral colonies. Reefs were grouped by coral cover.
The Antarctic soft-shell clam (Laternula elliptica) lives buried in mud on the sea bed, where the water is normally about 0 °C. Clams were kept at different temperatures for two weeks, then placed on mud, and the percentage that could bury themselves was recorded.
You will need: Two identical clear bottles, thermometers or probes, lamp, vinegar and sodium hydrogen carbonate
Safety: Eye protection. Lamps get hot. Keep bottles open while generating gas, to avoid pressure build-up.
Carry this out with your teacher's supervision and follow your school's lab rules.
Arrhenius calculated the warming effect of carbon dioxide in 1896. Today the IPCC brings thousands of scientists together to assess the evidence.
Consensus is not proof, yet it is meaningful. Consider how non-experts should decide whom to trust on complex issues.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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