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

1. 1
   Nairobi, Kenya, lies almost on the equator and has two rainy seasons a year, when the zone of rising air known as the Intertropical Convergence Zone (ITCZ) passes overhead. Cairo, Egypt, lies near 30° N and typically receives under 30 mm of rain a year. Both cities have similar hours of daylight for much of the year.

   (a)

   Which statement best explains why the equator receives more solar energy per unit area than the poles?

   [1 mark]

   • AThe equator is much closer to the Sun than the poles are
   • BThe equator has more greenhouse gases above it than the poles
   • CThe Sun's rays strike the equator at a steeper angle, so the energy is spread over a smaller area and passes through less atmosphere
   • DThe poles are covered by ice, which stops sunlight reaching them

   (b)

   In the tricellular model of atmospheric circulation, what happens to air at about 30° N and 30° S?

   [1 mark]

   • AIt rises, cools and releases heavy rain
   • BIt sinks, warms and becomes dry, producing desert conditions
   • CIt moves directly from the equator to the poles at ground level
   • DIt stays at the same height and does not move

   (c)

   Explain why Nairobi has high rainfall while Cairo is dry.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In rural northern India, many households cook on open fires or simple stoves that burn wood and cow dung. These release black carbon, tiny dark particles of soot. Winds carry black carbon over long distances and some of it settles on Himalayan snow and glaciers. While suspended in the air, black carbon also absorbs sunlight.

   (a)

   Black carbon is best described as

   [1 mark]

   • Aa greenhouse gas formed by the reaction of nitrogen with oxygen
   • Ba gas that destroys stratospheric ozone
   • Ca liquid droplet formed by condensation of water vapour
   • Dan aerosol made of solid particles suspended in the atmosphere

   (b)

   What is the effect of black carbon settling on snow and glaciers?

   [1 mark]

   • AIt lowers the albedo, so more solar radiation is absorbed and melting speeds up
   • BIt raises the albedo, so more solar radiation is reflected
   • CIt has no effect because snow is always white
   • DIt cools the snow by emitting infrared radiation to space

   (c)

   Suggest how replacing open fires with cleaner stoves could reduce the rate of warming in the region.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student compares three planets using published data. Earth: mean surface temperature 15 °C, atmosphere about 0.04% carbon dioxide, distance from the Sun 1.00 AU. Venus: mean surface temperature about 465 °C, atmosphere about 96% carbon dioxide at a surface pressure about 92 times that of Earth, distance 0.72 AU. Mars: mean surface temperature about -63 °C, atmosphere about 95% carbon dioxide but at a surface pressure only about 0.6% of Earth's, distance 1.52 AU. Calculations suggest that Earth, without any atmosphere, would have a mean surface temperature of about -18 °C.

   (a)

   Calculate the difference between Earth's actual mean surface temperature and the temperature it would have with no atmosphere, and state how greenhouse gases cause this difference.

   [3 marks]

   (b)

   Using the data, evaluate whether distance from the Sun alone explains the surface temperatures of Venus and Mars.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A letter to a local newspaper states: "Scientists want to cut greenhouse gas emissions because the greenhouse effect is damaging our planet. We would be better off if the greenhouse effect did not exist."

   (a)

   Explain how the greenhouse effect warms the Earth.

   [6 marks]

   (b)

   Evaluate the claim made in the letter.

   [6 marks]

   Total for question 4: 12 marks

End of questions