Climate change - mitigation and adaptation practice questions.

A coastal city raises its flood defences and installs pumping stations to clear seawater from low-lying districts. This response is best classified as

• mitigation, because it lowers the concentration of greenhouse gases in the atmosphere
• adaptation, because it reduces vulnerability to an impact
• adaptation, because it reduces the city's own greenhouse gas emissions
• mitigation, because it removes the cause of the rise in sea level

Answer: adaptation, because it reduces vulnerability to an impact

Mitigation acts on the causes - the emissions and sinks that drive the change - while adaptation acts on the consequences. Sea defences do nothing to slow sea level rise; they reduce the harm it causes.

Which climate strategy works by enlarging a carbon sink rather than by reducing emissions at source?

• replacing coal-fired power stations with wind farms
• improving the insulation of the existing housing stock
• reforesting degraded upland catchments
• raising the fuel efficiency standard required of new cars

Answer: reforesting degraded upland catchments

A sink moves carbon out of the atmospheric storage into biomass and soil, whereas the other three reduce the flow of carbon into the atmosphere but remove none of what is already there.

It has been proposed that sulfate aerosols could be injected into the stratosphere to cool the planet. The main environmental objection is that this would

• remove carbon dioxide from the atmosphere and so reduce ocean acidification
• lower planetary albedo and so accelerate the warming it aims to stop
• convert stratospheric ozone directly into photochemical smog at ground level
• raise planetary albedo but leave carbon dioxide unchanged

Answer: raise planetary albedo but leave carbon dioxide unchanged

Solar radiation management treats a symptom: it cuts the incoming shortwave flow, but the carbon dioxide storage keeps growing, so ocean acidification continues and the cooling would end abruptly if the injections stopped.

A public health campaign persuades people to replace part of the beef in their diet with pulses. The largest climate benefit of this shift comes from

• lower methane emissions from ruminant digestion
• lower nitrous oxide emissions from burning crop residues
• reduced release of halocarbons from food processing plants
• extra carbon dioxide taken up by the pulse crop itself

Answer: lower methane emissions from ruminant digestion

Cattle are the dominant agricultural source of methane, and each kilogram of beef also carries the land and feed grown to produce it. Carbon taken up by a food crop is returned when the food is digested, so it is not a net removal.

Two low-lying countries face the same rise in sea level over the next fifty years. The one likely to suffer far greater loss of life is the one with

• a higher proportion of its population living in inland highland areas
• less capacity to fund defences and early-warning systems
• a larger share of its territory lying above ten metres elevation
• a smaller total population living inside the coastal zone

Answer: less capacity to fund defences and early-warning systems

Impact is a product of exposure and of the capacity to adapt, so two societies facing the same hazard can experience very different outcomes. Vulnerability, not the hazard alone, decides how much damage a given change does.

A government commits its country to reaching net zero greenhouse gas emissions by a stated date. This commitment means that by that date

• remaining emissions are balanced by an equal removal from the air
• no greenhouse gas of any kind is released within the country
• emissions per person have fallen to the current global average level
• all electricity in the country is generated without combustion

Answer: remaining emissions are balanced by an equal removal from the air

Net zero accepts that some emissions, from cement, aviation and agriculture, will be very hard to eliminate, and requires an equal removal by sinks or engineered capture to offset them. The weakness of the target is that it can be met on paper by promising removals that do not yet exist at scale.