Describe on a molecular level how the greenhouse effect occurs.

Suggest two factors that influence the relative greenhouse effect of a gas.

allows (higher frequency) radiation from sun/incoming radiation to pass unhindered;

long wavelength/infrared/IR radiation radiated/emitted by Earth;

Do not accept reflected.

(some IR radiation is) absorbed by greenhouse gases;

Do not accept "trapped / blocked" or statements that refer to absorption of incoming IR radiation.

causes (increased) vibration in bonds;

Accept “causes (increased) bond stretching/bending/deformations”.

emits/re-radiates IR radiation (some of which returns to Earth);

Do not accept “heat/IR radiation reflects/bounces”.

Any two for [1] of:

abundance/concentration (in atmosphere)

strength/intensity/power of IR absorbance / ability to absorb heat radiation

lifetime/duration / rate of depletion/decomposition in atmosphere;

Many students could identify another greenhouse gas and a source, usually CFCs, but it was surprising how many did not read the “other”! It was disappointing how few students could accurately explain the greenhouse effect – the term “reflect” was used too often and, in addition, many continue to confuse it with ozone depletion and acid rain. Only a handful of students could identify the factors that affect how much various gases contribute to the overall effect. In the final part of the question a major weakness was a failure to link an effect with a consequence.

Many students could identify another greenhouse gas and a source, usually CFCs, but it was surprising how many did not read the “other”! It was disappointing how few students could accurately explain the greenhouse effect – the term “reflect” was used too often and, in addition, many continue to confuse it with ozone depletion and acid rain. Only a handful of students could identify the factors that affect how much various gases contribute to the overall effect. In the final part of the question a major weakness was a failure to link an effect with a consequence.