| Date | May 2019 | Marks available | 3 | Reference code | 19M.2.SL.TZ0.4 |
| Level | SL | Paper | 2 | Time zone | no time zone |
| Command term | Explain | Question number | 4 | Adapted from | N/A |
Question
The rise in global temperatures has led to the melting of the sea ice in polar regions. Scientists have developed a number of computer models that can be used to make predictions about the rate of sea ice melting in these polar regions and its effect on coastal areas globally. In order to create a computer model a number of variables are identified.
A computer model of the effects of the melting of the sea ice in the Arctic Ocean may include the following variables:
- average ocean surface temperature (°C)
- albedo of the ocean (the proportion of light reflected from the ocean surface)
- precipitation (mm)
- salinity of the ocean (grammes of salt in one kilogramme of water)
- area of sea ice (km2).
In this model the following rules have been determined:
- for every 0.01 °C increase in ocean surface temperature, the area of sea ice decreases by 1 %
- for every 1 % decrease in the area of the sea ice, the sea level rises by 20 mm.
The initial values are:
- area of sea ice = 1 000 000 km2
- average surface temperature of the ocean is 0.00 °C.
The scientists observed when running the model numerous times using historical data there were significant differences between observed and expected results.
A second model was developed that included new variables and rules.
The surface of the ocean reflects the heat from the sun. The ratio between the area covered by the sea ice and the area where there is no sea ice (open ocean) affects the value of the average albedo. The lower the albedo, the quicker the sea ice will melt.
The average albedo is calculated using this formula:
Average albedo =
Note:
- area of sea ice = 1 000 000 km2
- area of open ocean = 1 000 000 km2
- albedo of sea ice = 0.6
- albedo of open ocean = 0.1.
The average albedo will change with every iteration of the model. Each iteration is 2 years after the previous.
The rules for the model are:
- the initial albedo is 0.35
- the rate of decrease in sea ice every 2 years is
- the starting year is 2019
- the sample rate is every 2 years.
Copy and complete the following table showing each variable’s data type and a suitable range of values that would represent the information shown above.
Using the rules and initial values above, construct the pseudocode that would enable the area of the sea ice and the sea level rise to be calculated if there was an increase of 0.04 °C in the ocean surface temperature.
Using the information above state the area of the sea ice.
Using the information above state the change in sea level.
Using the formula, rules and initial data given above, construct the pseudocode that would calculate the year that the area of sea ice will be less than 10 000 km2.
Identify two ways that this model could be implemented.
Explain why the accuracy of the simulation in predicting the area of the sea ice is critical.
Markscheme
Award [3 max]. 
Award [4 max].
Initialization – Original area of sea ice;
Initialization – Surface temperature change;
New sea ice area calculation;
Sea level change calculation;
Example algorithm:
OriginalSeaIceArea = 1000000
SurfaceTempChange = 0.04
NewSeaIceArea = OriginalSeaIceArea * (1 – SurfaceTempChange)
SeaLevelChange = -(NewSeaIceArea - OriginalSeaIceArea) / OriginalSeaIceArea * 100 * 20
Award [1 max].
960 000 (km2);
Award [1 max].
80 (mm);
Award [7 max].
Initialization – Initial areas of Ice and water, and starting year;
Use of loop;
Loop parameters (limits, condition, increment, end statement correct);
Average albedo;
Rate of decrease calculation;
Area of ice update calculation;
Area of open water update calculation;
Output;
Example algorithm:
IceArea = 1000000
OpenArea = 1000000
Year = 2019
Loop While IceArea > 10000
TotalArea = IceArea + OpenArea
AveAlbedo = ((IceArea * 0.6) + (OpenArea * 0.1)) / (IceArea + OpenArea)
Decrease = 0.3 / (AveAlbedo * AveAlbedo)
// allow Decrease = 0.3 / AveAlbedo ^ 2
IceArea = IceArea * (1 − (0.01 * Decrease))
OpenArea = TotalArea − IceArea
Year = Year + 2
End loop
Output "Date when there less than 10 000km2 of ice in the ocean
is " Year
Award [2 max].
Spreadsheets;
IDEs using code;
Award [3 max].
If the calculation of the rate of reduction of the sea ice is inaccurate the calculation of the amount of sea ice remaining;
At a given time will turn out to be wrong;
So, work to correct the problems may be too little/too great;
The year in which the sea ice is predicted to be 10 000 km2;
Will be wrong;
So, ice coverage may be more/less than expected in the calculated year;
Examiners report
Most candidates recognized this as a straightforward question. However, some candidates were unable to demonstrate the concept of data types and range of values for given variables.
This question was reasonably well answered and most candidates were able to produce some pseudocode. However, a few candidates struggled to apply all the required formulae and couldn’t produce all the required values.
The question was answered correctly by most of the candidates.
The question was answered correctly by most of the candidates.
The vast majority of candidates could not produce the correct pseudocode to calculate all the required values.
The skill to apply a loop in this question was poorly demonstrated by most of the candidates.
The question was not well understood by the majority of the candidates. Most of the responses were generic and off course.
Most candidates did not answer the question appropriately and focused more on generic points rather than being specific to the scenario.
