6.1 Introduction to the atmosphereIB Environmental Systems and Societies HL: Subtopic test

1. 1
   Manaus, in the Amazon basin close to the equator, receives more than 2 000 mm of rain a year. Arica, in the Atacama Desert of northern Chile at about 18° S, receives only a few millimetres of rain a year, and parts of the Atacama go years without measurable rain.

   (a)

   Which statement correctly describes conditions in the air above Manaus?

   [1 mark]

   • AThe air is sinking, warming and becoming drier
   • BThe air is cold and dense and flows from the poles
   • CThe air flows horizontally with no vertical movement
   • DThe air is heated, rises and cools, so water vapour condenses to form heavy rain

   (b)

   What is the overall result of the tricellular model of atmospheric circulation?

   [1 mark]

   • AHeat is moved from the poles to the equator
   • BHeat is redistributed from the equator towards the poles
   • CThe atmosphere stops moving at 30° latitude
   • DHeat is lost from the equator to space only

   (c)

   Explain why Arica receives so little rainfall.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Mount Everest is 8 849 m high. Air pressure is about 1 013 hPa at sea level, about half of that at an altitude of 5.5 km and about one third of it at the summit. Oxygen makes up about 21% of the air at every altitude, yet climbers above 8 000 m usually breathe bottled oxygen because each breath contains far fewer oxygen molecules.

   (a)

   Why does air pressure decrease as altitude increases?

   [1 mark]

   • AAir is heated by the Sun at high altitude and expands upwards without limit
   • BOxygen is converted to ozone at high altitude
   • CGravity pulls air molecules towards the Earth's surface, so the air is densest near the surface and thins with altitude
   • DMountain peaks absorb air molecules

   (b)

   Which statement about oxygen at the summit of Mount Everest is correct?

   [1 mark]

   • AThe percentage of oxygen is about the same as at sea level, but each breath contains fewer oxygen molecules
   • BThe percentage of oxygen is much lower than at sea level because it is used up by climbers
   • CThe percentage of oxygen is higher than at sea level
   • DThere is no oxygen at the summit

   (c)

   Explain, with reference to gravity, why the atmosphere becomes thinner with increasing altitude.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student looks up data on three greenhouse gases. Approximate concentrations: carbon dioxide 420 ppm, methane 1.9 ppm, nitrous oxide 0.34 ppm. Approximate 100-year global warming potentials (the warming caused by 1 tonne of the gas compared with 1 tonne of carbon dioxide): carbon dioxide 1, methane 28, nitrous oxide 265. Methane stays in the atmosphere for about 12 years, whereas carbon dioxide persists for centuries. Sources of methane include cattle, rice paddies, landfill sites and leaks from fossil fuel extraction.

   (a)

   Calculate the carbon dioxide equivalent of 2.5 million tonnes of methane, and explain what the global warming potential tells you.

   [3 marks]

   (b)

   Using the data, discuss why methane receives a lot of attention in climate policy even though its concentration is much lower than that of carbon dioxide.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Ice cores from Antarctica record cycles of cold glacial periods and warmer interglacial periods that repeated roughly every 100 000 years during the Quaternary (the last 2.6 million years). The Earth's orbit and axis change in regular ways: the shape of the orbit varies over about 100 000 years, the tilt of the axis varies over about 41 000 years and the axis wobbles over about 21 000 to 23 000 years. Much earlier, about 2.4 billion years ago, the atmosphere contained almost no free oxygen until photosynthetic bacteria (cyanobacteria) became abundant.

   (a)

   (HL) Explain how Milankovitch cycles cause glacial and interglacial periods, and how current warming differs from these natural changes.

   [6 marks]

   (b)

   (HL) Explain how the evolution of life has changed the composition of the atmosphere, and how this has influenced the evolution of life.

   [6 marks]

   Total for question 4: 12 marks

End of questions