| Date | November 2012 | Marks available | 3+3 | Reference code | 12N.1.bp.3 |
| Level | SL and HL | Paper | 1 | Time zone | |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
The graph shows several different ways of cooling the Earth by geo-engineering (the use of engineering to resolve environmental issues).
[Source: Jim Giles (29 March 2010), Hacking the Planet: Who Decides? New Scientist, issue 2754]
Identify the two most cost-effective options shown on the graph.
Explain how deforestation may contribute to global warming.
Explain two possible environmental consequences of global climate change.
Markscheme
Award [1 mark] for stratospheric sunshade and [1 mark] for afforestation.
Deforestation – burning of forests releasing CO2 / removes a valuable carbon sink [1 mark]
Increases CO2 in the atmosphere [1 mark]
CO2 is a greenhouse gas linked to global warming, through its role in helping raise the quantity of heat energy retained by the atmosphere [1 mark].
Credit should be given in a similar fashion to answers that refer to deforestation resulting in changed albedo.
The answer needs to focus on the loss of the trees – not on what replaces the trees for example, cattle ranching and methane.
The consequences may be at any scale and there are many possible answers.
Possible consequences include:
- rising sea levels [1 mark] due to thermal expansion [1 mark] floods lowlands [1 mark]
- melting ice / Earth’s albedo reduced/increased intake of solar radiation / warms climate further
- increased temperature of oceans / greater incidence of tropical storms / devastation caused by hurricane Sandy in Haiti, Cuba
- melting ice releasing freshwater into North Atlantic / shuts down ocean / may lead to falling temperatures in Europe.
Other possibilities: extinctions, moving biomes, bleaching of coral reefs, desertification, etc.
In each case, award [1 mark] for identifying a valid consequence with a further [2 marks] for two distinct points in the explanation, one of which could be exemplification.
Examiners report
Straightforward but the lack of units on the graph seemed to confuse some candidates.
Most responses had excellent knowledge and understanding of how deforestation leads to global warming with reference to forests being carbon sinks or increases via burning and how the increase in greenhouse gases led to the trapping of long wave radiation.
Most candidates could include valid consequences. They were able to identify a consequence such as rising sea levels and give an explanation of how this occurred. Weaker responses were characterized by very limited explanation. There were some who drifted from the environmental element of the question and explained the impacts on human activity, which was self-limiting.
