D4.3 Climate change. Practice questions with markscheme.

• B: chicks are reared on the landfast ice and cannot survive in water until they fledge; if the ice breaks out before fledging the chicks are lost; adults are strong swimmers so open water helps rather than hinders feeding (A), eggs are incubated on the adults' feet, not directly on ice (C), and krill live in the open ocean (D);

• D: interacting species can shift their seasonal timing (phenology) at different rates, decoupling events that evolved to coincide;

• A: warming extends vector/pest ranges and (usually) increases generations per year; III is backwards;

• C: short-wave solar radiation passes through; the surface re-emits long-wave radiation, which greenhouse gases absorb and re-emit, warming the lower atmosphere;

• B: CO₂ (fossil fuels, deforestation) and CH₄ (agriculture, waste, fossil-fuel extraction) are the main anthropogenic greenhouse gases;

• nutrients (nitrate / phosphate) in surface water are used up by phytoplankton and sink to deep water in dead organisms / faeces;
• upwelling of (cold) deep water, driven by ocean currents / winds, returns nutrients to the surface;
• warmer surface water is less dense, so it forms a stable layer that prevents / delays upwelling (or currents change so the timing and extent of upwelling are altered), OWTTE;
• phytoplankton become nutrient-limited, so primary production / photosynthesis decreases;
• less energy is fixed at the base of the food chain, so less is available to zooplankton, fish and higher trophic levels (and fisheries decline), OWTTE;

Do not accept 'less oxygen' as the reason for reduced production.

• axes labelled: pH of the seawater on the horizontal axis, with the direction of the scale shown, and rate of calcification on the vertical axis;
• the rate of calcification is highest at the highest (present-day) pH;
• the rate falls as pH falls / as the seawater becomes more acidic;
• the line reaches zero, or becomes negative (net dissolution of calcium carbonate), at the lowest pH values;

Accept a straight line or a curve. No numerical values are required; credit shape and trend only.

• burning of fossil fuels (and cement production) releases CO₂;
• deforestation reduces CO₂ uptake (and releases carbon when burned);
• agriculture/livestock/waste release methane (and nitrous oxide);
• (so) atmospheric greenhouse-gas concentrations have risen (far) above pre-industrial levels;
• greenhouse gases absorb long-wave radiation emitted by Earth and re-radiate it, retaining heat;
• the enhanced greenhouse effect raises global mean temperature;
• positive feedback: melting ice lowers albedo, so more radiation is absorbed → more warming;
• positive feedback: thawing permafrost releases CH₄/CO₂ → more warming;
• warmer oceans absorb less CO₂ (and hold more water vapour, itself a greenhouse gas), OWTTE;

• positive feedback: warming triggers a change that causes further warming (self-reinforcing);
• albedo/ice loss: melting sea ice replaces reflective white surface with dark ocean, which absorbs more radiation;
• permafrost thaw releases methane and CO₂ from decomposing organic matter;
• (warming oceans hold less dissolved CO₂ / droughts and fires release forest carbon);
• each loop's product feeds its cause, so change can accelerate once thresholds/tipping points are passed;
• (hence) warming may continue even if emissions fall, an argument for early action, OWTTE;