| Date | November 2011 | Marks available | 3 | Reference code | 11N.3.sl.TZ0.E2 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | E2 | Adapted from | N/A |
Question
The temperature of the Earth is increasing. There is considerable scientific evidence to suggest this is due to an increase in the concentration of greenhouse gases as a result of human activity.
Explain how this enhanced greenhouse effect causes the average temperature of the Earth to increase.
Compare the contributions of carbon dioxide and methane to the enhanced greenhouse effect.
Markscheme
incoming solar radiation is short(er) wavelength/high(er) frequency/high(er) energy radiation / UV radiation;
(re-)radiated/emitted (by the Earth’s surface) as long(er) wavelength/low(er) frequency/ low(er) energy/IR radiation;
the energy is absorbed in bonds in greenhouse gases / the molecules vibrate when IR radiation is absorbed;
the energy is (re-)radiated/(re-)emitted as IR radiation;
carbon dioxide is more abundant;
methane is more effective at absorbing IR radiation;
Award [1] for statement that “CO2 is more abundant and CH4 is more effective”
with no mention of “at absorbing IR radiation”.
Accept converse arguments.
Examiners report
It was surprising to see that many candidates could not score full marks in a question on the greenhouse effect which appears often in examination papers. The use of unacceptable language (reflecting, bouncing, trapping, etc.) cost many candidates marks.
Although most knew that carbon dioxide was more abundant, far fewer could clearly express the point about methane being better at absorbing IR radiation.
