6.2 Climate change — causes and impactsIB Environmental Systems and Societies HL: Subtopic test

1. 1
   The Great Barrier Reef off Queensland, Australia, has suffered mass coral bleaching in several recent summers, including 2016, 2017, 2020 and 2022, when sea temperatures stayed well above the normal summer maximum for several weeks. In bleaching, corals expel the symbiotic algae that live in their tissues and supply most of their food and colour. Reefs given several years to recover can regrow, but repeated events have left some sections with much lower coral cover. The reef supports tourism and fishing businesses along the Queensland coast.

   (a)

   What causes coral bleaching on the Great Barrier Reef?

   [1 mark]

   • AIncreased ultraviolet radiation from ozone depletion
   • BOverfishing of herbivorous fish
   • CSea temperatures remaining abnormally high for several weeks, causing corals to expel their algae
   • DAcid rain falling directly on the reef

   (b)

   Which statement about the resilience of the Great Barrier Reef is correct?

   [1 mark]

   • AResilience is unaffected by repeated bleaching
   • BResilience is the number of tourists the reef can support
   • CA reef with high resilience never changes
   • DRepeated bleaching events with little time for recovery reduce the reef's resilience

   (c)

   Explain how repeated mass bleaching could affect the people of coastal Queensland.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Researchers reconstruct past climates using (i) pollen grains identified at different depths in a peat core from a Scottish bog, (ii) the ratio of oxygen isotopes in Antarctic ice cores and (iii) the widths of annual rings in long-lived oak trunks. In addition, weather stations, satellites and observatories record temperature and gas concentrations directly. The team also tests a global climate model by running it with conditions from past decades and comparing its output with the records.

   (a)

   Which of these is an indirect measurement (proxy) of past climate?

   [1 mark]

   • ATemperature recorded by a weather station
   • BPollen preserved in a peat core
   • CCarbon dioxide concentration measured at an observatory
   • DRainfall recorded by radar

   (b)

   What is hindcasting?

   [1 mark]

   • ARunning a climate model using past conditions and comparing its output with recorded past climate to test its validity
   • BPredicting climate for the next century
   • CCounting tree rings to find the age of a tree
   • DMeasuring greenhouse gas concentrations in ice

   (c)

   Explain how pollen in a peat core can provide information about past climates.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In 2022 floods in Pakistan affected about 33 million people and killed more than 1 700; roughly a third of the country was under water, and many poorer rural households lost homes, crops and livestock. In 2022 Pakistan emitted under 1% of global carbon dioxide emissions, about 1 tonne per person per year, while the United States emitted about 13% of the global total, about 14 tonnes per person per year.

   (a)

   Describe how the 2022 floods affected society at different scales and how socio-economic conditions influenced the impact.

   [3 marks]

   (b)

   (HL) Using the data, discuss the political and economic implications of the fact that countries differ in their responsibility for and vulnerability to climate change.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Climate scientists warn that the Amazon rainforest and the Greenland ice sheet are two parts of the climate system that could pass thresholds. In the Amazon, deforestation and drought reduce transpiration and rainfall, which can turn rainforest into dry savanna. Greenland's ice sheet is melting faster as it loses surface height and reflectivity. A commentator writes: "The Earth has already passed the planetary boundary for climate change, so it is too late for our efforts to make any difference."

   (a)

   Evaluate the commentator's claim that, because the planetary boundary for climate change has been passed, efforts to act are pointless.

   [6 marks]

   (b)

   (HL) Explain what is meant by a tipping point and how tipping cascades could develop in the climate system.

   [6 marks]

   Total for question 4: 12 marks

End of questions