• Atmospheric/tri-cellular circulation (including Hadley, Ferrel & polar cells) creates patterns of climate that determine dominant vegetation types 1 mark

• Low pressure due to intense heating/high insolation at the equator causes rising moist air in the tropics, creating high precipitation giving rise to rainforests 1 mark

• Moving polewards (at high altitude), air cools, becomes denser and sinks forming a high-pressure zone/descending dry air (20–30° latitude/tropics) creates water-limiting/arid conditions giving rise to deserts 1 mark

• Some air continues towards the poles to equalize temperature difference/atmosphere transfers heat from (sub-)tropics to mid-latitudes giving rise to temperate biomes 1 mark

• Descending/dry air (high latitude/polar regions) creates water-limiting conditions in tundra 1 mark

4 marks max

Human impacts on the atmosphere affecting terrestrial biome productivity

• Increased greenhouse gas emissions (e.g. $\text{CO}_2$, $\text{CH}_4$, $\text{N}_2\text{O}$) from burning of fossil fuels/deforestation enhance the greenhouse effect 1 mark

• This leads to global warming/climate change which can:

  • Shift biome boundaries polewards/to higher altitudes 1 mark
  • Increase frequency/intensity of extreme weather events (e.g. droughts, floods) 1 mark
  • Disrupt phenological events/timings (e.g. earlier bud burst) 1 mark

• Increased temperatures can increase productivity in some biomes (e.g. tundra, boreal forests) but decrease productivity in others (e.g. deserts, tropical rainforests) 1 mark

• Increased atmospheric $\text{CO}_2$ can increase photosynthetic rates/productivity (CO$_2$ fertilization effect) 1 mark

7 marks max

Answers may include:

• understanding concepts and terminology of biodiversity; conservation strategies; tropical biomes; rainforests; swamps; coral reefs; hotspots; LEDCs & MEDCs; international v national conservation bodies; environmental value systems; productivity; carbon sinks; global warming; unsustainable exploitation; resources of tropical ecosystems; medicines; indigenous cultures; endangered species; Red List, etc.;
• breadth in addressing and linking threats to biodiversity with different societies, ecosystems, conservation strategies; the global dependence upon and significance of tropical biomes compared with others; implications of economic development in tropical regions with challenges of conservation; different EVS perspectives on reasons for conservation, etc.;
• examples of tropical biomes/ecosystems; their local societies; conservation efforts; reasons/needs for conservation, etc.;
• balanced analysis evaluating the extent to which conservation efforts are of particular importance for tropical biomes along with relevant limitations and counterarguments, etc.;
• a conclusion that is consistent with, and supported by, analysis and examples given e.g. “although the loss of any species may be considered of equal significance from an ecocentric point of view, the high productivity and biodiversity that characterize tropical biomes, along with the limited facility of local societies, which are often less developed, make tropical biomes a priority for international conservation efforts”;