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.

The table shows measurements for an industrial region over five decades. Which statement is best supported by the data?

• Sulphur dioxide emissions fell steadily throughout the period
• Surface solar radiation reached its highest recorded value in the decade with the greatest emissions
• The decline in surface solar radiation was reversed after emissions fell
• Surface solar radiation changed independently of sulphur dioxide emissions

Answer: The decline in surface solar radiation was reversed after emissions fell

Reflective sulphate aerosols scatter incoming shortwave radiation back to space, so radiation reaching the surface falls while emissions rise and recovers once they are controlled. This dimming signal partly masked greenhouse warming in industrial regions.

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.

The table shows monitoring data for a hypothetical reef system. Which statement is supported by these data alone?

• Bleaching increased every year without exception between 2015 and 2021
• The percentage of bleached sites rose and fell with the temperature anomaly
• Bleaching was caused by acidification rather than by rising temperature
• The whole reef system recovered fully in 2021 once the anomaly fell below +1.2 °C

Answer: The percentage of bleached sites rose and fell with the temperature anomaly

The data show covariation between anomaly and bleaching extent, nothing more: 2021 falls on both variables, so 'every year' is wrong, and neither causation by acidification nor full recovery can be read from a table of percentages.