| Date | May 2015 | Marks available | 3 | Reference code | 15M.2.HL.TZ2.1 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Discuss | Question number | 1 | Adapted from | N/A |
Question
Global warming has changed both the thickness and surface area of sea ice of the Arctic Ocean as well as the Southern Ocean that surrounds Antarctica. Sea ice is highly sensitive to changes in temperature.
Scientists have calculated a long-term mean for the surface area of sea ice in the Arctic and in the Southern Ocean around Antarctica. This mean value is used as a reference to examine changes in ice extent. The graph shows the variations from this mean (zero line) over a period of time.
Adélie penguins (Pygoscelis adeliae) are only found in Antarctica and need sea ice for feeding and nesting. Biologists are able to deduce how these penguins have responded to changes in their environment for the last 35 000 years, as the Antarctic conditions have preserved their bones and their nests. The image is a map of Antarctica and the surrounding Southern Ocean. It shows the trends in the length of the sea ice season (days of the year when sea ice is increasing) and the sites of nine Adélie penguin colonies.
State the trend in the surface area of sea ice in the Southern Ocean around Antarctica.
Distinguish between changes in the surface area of sea ice in the Arctic and Antarctica.
Discuss the data as evidence of global warming.
Describe the trends in the length of the sea ice season around the Antarctic Peninsula and in the Ross Sea.
Analyse the trends in colony size of the Adélie penguins in relation to the changes in the sea ice.
Discuss the use of Adélie penguins in studying the effects of global warming.
Markscheme
increasing/positive trend/correlation;
a. in the Arctic ocean the surface area of sea ice has declined whereas in Antarctica the surface area has increased;
b. the rate of change is greater for the Arctic than for Antarctica;
c. there are greater fluctuations in the surface area of sea ice in Antarctica than in the Arctic;
For mp a, it is acceptable if there is no comparative term such as “whereas” or “but”;
a. change / decrease / melting of sea ice is expected with global warming;
b. decrease of sea ice in Arctic is supportive evidence of global warming;
c. increase in sea ice in Antarctic is not supportive evidence of global warming;
d. Antarctic increase / both changes may be associated with climate change (caused by global warming);
e. global warming does not affect all areas in the same way / global warming has complex effects;
f. data is inconsistent/inconclusive / data on its own does not establish cause and effect / not over a very long period of time;
One mark for correct description of the trend off the Antarctic Peninsula and one mark for correct description for the Ross Sea; accept correct statements other than those listed in the scheme but do not award a mark for contradictions; marks can be awarded for correct statements about the sea ice season for Antarctica overall; Some students are referring to moving South in the Ross Sea when it is
clear that they are moving North. If you can discern their intention, then give the BOD on this;
Antarctic Peninsula:
a. decrease/stable at the base of the peninsula / decrease in the area of the penguin colonies/West of the tip / increase/+1 above and below the peninsula / variable pattern;
Ross Sea:
b. sea ice is increasing / +1 in the Ross Sea / area below / North of the Ross Sea / lower Ross Sea / Southern part of Ross Sea/closest to the South pole is stable/no change to the length of the sea ice season / variable pattern;
a. (off AP) sea ice season has declined as has penguin population;
b. colony 2 and 3 sea ice season has not declined and population increased;
c. colony 3 increase in population and growing length of sea ice season;
d. colony 2 has stable / increasing numbers and sea ice season is not changing;
e. colony size and sea ice season length/area are correlated;
f. Population numbers for colony 1 and 3 the same at start of study but both experience a big (opposite change);
Accept answers that refer to “sea ice” or “sea ice area”.
a. global warming leads to climate / environmental change; eg temperature change / ice melting
b. stable ice associated with stable population / no climate change;
c. ice changes associated with population changes;
d. changes in penguin population size can indicate climate change / global warming;
e. example of how climate change can alter population; eg prey availability / habitat loss;
f. not all species will be affected in the same way (so care needed in applying conclusions more widely)
g. there is information on changes of population over the past 35 000 years;
Examiners report
Nearly all students noted the positive trend.
Most students noted that while the Arctic showed a decline, Antarctica showed an increase. Weaker answers involved a descriptive account or failed to notice a second difference between the Arctic and Antarctic data. Noting that the rate of change for the Arctic was greater was more commonly included in answers than detecting that the data was more variable for Antarctica.
Most candidates noted that the data for Antarctica was supportive evidence of global warming. Weaker answers failed to state that the data was equivocal; strong candidates suggested global warming could lead to climate change with different outcomes in different locations.
Some respondents on the G2 forms raised concerns about the presentation of the data but most students earned these marks. A broad range of answers were accepted.
A number of candidates failed to link sea ice changes to population size changes. Better answers differentiated between colony 2 being stable and colony 3 having a growing ice season.
Many answered that penguin population changes could be used as indicators of the effects of global warming. Few extended the discussion to refer to historical data or limits to generalizing effects on penguins to other species.
