Core: Global climate - vulnerability and resilience practice questions.

Which natural cause of climate change operates on a timescale of tens of thousands of years and paces the glacial-interglacial rhythm?

• The 11-year sunspot cycle
• Explosive volcanic eruptions injecting aerosols
• The El Nino-Southern Oscillation
• Milankovitch orbital cycles

Answer: Milankovitch orbital cycles

Eccentricity, axial tilt and precession redistribute insolation over roughly 23 000 to 100 000 years, which is why they set the pace of ice ages. Volcanic, ENSO and solar-cycle forcings act over years to a decade and cannot explain a 100 000-year cycle.

Which of these processes acts as a negative, that is stabilising, feedback in the global climate system?

• Methane released from thawing permafrost in Siberia, Russia
• Faster plant growth taking up more carbon as CO2 rises
• Lower surface albedo as Arctic sea ice retreats
• More atmospheric water vapour as the lower atmosphere warms

Answer: Faster plant growth taking up more carbon as CO2 rises

A negative feedback damps the original change, and extra carbon taken up by stimulated plant growth removes some of the gas that caused the warming. The other three amplify the initial change, because 'positive' in this context means self-reinforcing, not beneficial.

Global mean sea level rose by about 0.20 m between 1901 and 2018. Which pairing names the two processes that dominate this rise?

• Melting of Arctic sea ice and increased river discharge into the oceans
• Subsidence of ocean basins and increased rainfall falling over the oceans
• Thermal expansion of ocean water and melting of land-based ice
• Melting of Arctic sea ice combined with thermal expansion of ocean water

Answer: Thermal expansion of ocean water and melting of land-based ice

Floating sea ice already displaces its own weight, so its melting adds almost nothing to sea level; only ice stored on land (Greenland, Antarctica, mountain glaciers) plus the expansion of warming water raise the ocean surface.

Glaciers in Peru's Cordillera Blanca have been retreating for decades. Their meltwater feeds the Rio Santa, on which irrigation, hydropower and coastal water supply in the Callejon de Huaylas and on the Pacific coast depend during the dry season. Which description best fits the medium-term water supply consequence?

• Dry-season flow falls at once and then recovers as more ice melts
• Dry-season flow is unaffected, because rainfall replaces the lost meltwater
• Dry-season flow rises permanently, because more ice melts every year
• Dry-season flow rises at first, then falls as the ice store shrinks

Answer: Dry-season flow rises at first, then falls as the ice store shrinks

A shrinking glacier is a store being emptied: melt output exceeds input for a while, so rivers run high, but once the ice volume is small the dry-season buffer disappears. The apparent water surplus is therefore a warning sign, not a gain.

A delta city raises its embankments and builds cyclone shelters so that residents can cope with more intense storm surges. Using the mitigation and adaptation categories applied to responses to global climate change, how are these measures best classified?

• Mitigation, because the works lower the city's greenhouse gas emissions
• Mitigation, because sea defences slow the rate of global warming
• Adaptation, because they change how people cope with the impacts
• Adaptation, because they cut greenhouse gas concentrations in the atmosphere

Answer: Adaptation, because they change how people cope with the impacts

In the climate-change categories, mitigation acts on the cause by cutting emissions or concentrations and adaptation acts on the consequences, so defences that reduce harm without changing emissions are adaptation however large the engineering. Take care: in the geophysical hazards option the word mitigation is used differently, for measures that reduce the damage a hazard does.

Under the Paris Agreement adopted in 2015, how are national emission targets arrived at?

• The UNFCCC secretariat allocates a legally binding emissions quota to every state
• Each state submits its own nationally determined contribution
• Only high-income states accept targets; all others are exempt until 2030
• Targets are auctioned between states in a single global carbon market

Answer: Each state submits its own nationally determined contribution

Paris is a bottom-up architecture: states pledge their own contributions and revisit them on a five-year cycle. The binding elements are procedural - reporting and review - not the emission figure itself.