(a)     Major greenhouse gases are water vapour and carbon dioxide. State two other greenhouse gases.

(b)     Describe how greenhouse gases cause the greenhouse effect.

(c)     Discuss three possible implications of global warming on world food production.

(a)     methane / \({\text{C}}{{\text{H}}_4}\);

nitrous oxide / \({{\text{N}}_2}{\text{O}}\);

ozone / \({{\text{O}}_3}\);

chlorofluorocarbons/CFCs / specific CFC / halocarbon /

hydrochlorofluorocarbons/HCFCs;

(b)     greenhouse gases / named gas(es) are transparent to/allow to pass through short(er)-wavelength / high(er)-energy radiation / UV light from Sun / OWTTE;

greenhouse gases/named gas(es) absorb long(er)-wavelength/IR radiation from Earth / OWTTE;

(part of) absorbed radiation is re-radiated to Earth / OWTTE;

(c)     droughts – food production decreases;

more rainfall – food production increases / may lead to flooding so decrease in food production;

warmer climate – food production increases;

severe weather / excessive rainfall / very hot climate – food production decreases;

deserts increase in size – food production decreases;

pests/insects multiply/spread over larger areas – food production decreases;

Allow other reasonable assumptions.

No mark if the effect on food/crops/plants is not explicitly stated.

Whilst most candidates could identify greenhouse gases correctly, many were distracted by gases associated with acid rain such as \({\text{S}}{{\text{O}}_{\text{x}}}\) and \({\text{N}}{{\text{O}}_{\text{x}}}\), a disappointingly small percentage could correctly explain how they affected the temperature of the earth with many confusing it with ozone depletion. Many candidates managed to score some marks on the effects of global warming, though often they failed to relate the change they were discussing to food production.