Flashcards · 0680 · Topic 4

The atmosphere and human activities flashcards

17 cards on Topic 4, subtopics 4.1 to 4.4. Pick a subtopic or study them all.

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What is the composition of dry air?: About 78% nitrogen, 21% oxygen, just under 1% argon and about 0.04% carbon dioxide. Water vapour varies.
Troposphere vs stratosphere: Troposphere: the lowest layer, holding most of the air, where weather happens. Stratosphere: the layer above, containing the ozone layer.
What is the natural greenhouse effect?: Gases such as carbon dioxide, methane, water vapour and nitrous oxide absorb heat radiated from the Earth’s surface and re-emit some back, keeping the Earth warm enough for liquid water and life.
Why is ozone helpful high up but harmful at ground level?: In the stratosphere it absorbs much of the Sun’s harmful ultraviolet radiation. At ground level it is a pollutant.

What is the enhanced greenhouse effect?: Extra warming caused when human activities add greenhouse gases to the atmosphere, so more heat is retained and average global temperature rises.
What are the main human sources of carbon dioxide, methane and nitrous oxide?: Carbon dioxide: burning fossil fuels, deforestation, cement making. Methane: rice paddies, cattle, landfill, gas leaks. Nitrous oxide: nitrogen fertilisers, burning biomass.
What are the impacts of climate change?: Rising sea level from thermal expansion and melting land ice, changing rainfall with more droughts and floods, changing crop yields, shifting habitats and species loss, and more heatwaves and extreme weather.
Mitigation vs adaptation to climate change: Mitigation reduces the cause: renewable energy, energy efficiency, tree planting, less deforestation. Adaptation copes with the effects: sea walls, drought-tolerant crops, water storage, early warning systems.

What causes acid rain?: Sulfur dioxide (from burning sulfur-containing fossil fuels and smelting ores) and nitrogen oxides (from vehicle engines and power stations) dissolve in water droplets to form acids. Normal rain is about pH 5.6; acid rain is lower.
What are the impacts of acid rain?: Acidified lakes and rivers harm fish and invertebrates; soils lose nutrients and release aluminium that damages tree roots; leaves are damaged; limestone, marble and metal structures corrode.
How can acid rain be reduced?: Flue-gas desulfurisation (scrubbers) in power stations, low-sulfur fuels or renewables, and catalytic converters on vehicles to reduce nitrogen oxides.
Why is liming a lake only a partial solution to acid rain?: It treats the effect, not the cause, so it must be repeated.
Why is acid rain an international problem?: Winds carry the gases across borders, so acid rain often falls in countries that did not produce the pollution.

What causes ozone depletion?: Chlorofluorocarbons (CFCs), once used in aerosols, refrigerators and foam packaging, reach the stratosphere, where ultraviolet light releases chlorine atoms that destroy ozone repeatedly.
What are the effects of ozone depletion?: More ultraviolet radiation reaches the surface, raising the risk of skin cancer and cataracts and harming plankton and crops.
What was the Montreal Protocol?: An international agreement of 1987 to phase out CFCs and similar substances, widely seen as successful international cooperation. The ozone layer is slowly recovering.
Is ozone depletion the main cause of global warming?: No. They are separate problems: ozone depletion lets in more ultraviolet radiation, while climate change is caused mainly by the enhanced greenhouse effect.