Arctic Sea Ice Time Series Report – Exemplar
Purpose and Introduction Statement
Climate change and global warming is one of the most talked about issues in the world today. An increase in extreme
weather events and rising global temperatures are evident. What has caused these changes is contentious and a matter
of much debate. However, the Arctic sea ice levels are one gauge that scientists use to monitor and track the changes in
climate.
In this study I will look at Arctic sea ice levels throughout the period 1990 and 2010. We will track the seasons and see
how the sea ice levels change throughout the year. However, our main purpose will be to track any changes in the long
term trend of the average Arctic sea ice area.
To further the study I will also look to see if we can track the data further into 2011 and 2012 as well as seeing if there is
any further historic data. I would also like to relate this time series to average global temperatures. As well, I will also
look at sea ice area levels in the Antarctic and see if I can find similar trends.
Time Series Graph
Main Feature of the Time Series
Long term trend:
Over the first three or so years it appears that the Arctic sea ice area increased slightly from approximately 9.5 million
km2 after which it then fluctuated down then back up over the next three to four. Since about 1997 however, the
overall long term trend for the area of sea ice in the Arctic is that it has continued to gradually decline. The trend has
fallen from approximately 9.5 million km2 in January 1997 to approximately 8.5 million km2 in March 2010. This
represents a decrease in sea ice area of approximately 1 million km2 over the given time period or a fall of about 6250
km2 per month since January 1997. The Holt Winters model, as seen on a later graph, would also suggest a linear long
term trend and one that continues on a gradual decline.
Seasonal trend:
The seasonal pattern of the Artic sea ice area levels is very consistent from year to year. Peak months are regularly
around February and March after which the ice tends to melt until the trough months of August and September where
the lowest area of sea ice is generally recorded. Peak sea ice areas average just under 4 million km2 above the trend,
while troughs tend to average around 5 million km2 under the trend. These peaks and troughs correspond with the
Northern hemisphere’s summer and winter months. The seasonal plot also tends to highlight that as the years pass, the
sea ice area, while regular in the seasonal patterns, does tend to decrease overall. This is however more the case in the
trough months than the peak months.
Residuals:
Overall the residuals are generally quite small and fall below 10% in regards to the contribution towards the variation in
sea ice areas (see table below). This means that the residuals in general can be considered to not be of any note. What
is of note however is that while having been fairly smooth between 1997 and 2007, the residuals have begun to vary
more over the last 3-4 years indicating that more unpredictable fluctuations are occurring and so residuals could begin
to be more of a concern in the future. There also one residual in September 2007 which does stand out and did seem to
have an impact on the raw data at that time.
Arctic sea ice area Minimum
Maximum
Range
2
(million km )
Raw data
2.5
13.5
Trend
8.5
9.5
Seasonal
-5
4
Residual
-1
1
Note that these are ball-park figures taken from the iNZight plots
Approx %
Contribution
11
1
9
2
1/11 x 100 = 9%
9/11 x 100 = 82%
What the table above does indicate as well is that most of the variation in the Arctic sea ice areas can be accounted for
by the seasonal component. 82% of the overall variation in this series can be accounted for by the seasonal component,
while the trend and the residual components account for the remaining variation.
Predictions
Using the Holt-Winters model, I have produced the predictions for the next two years, or 24 months. These are given in
the table below, along with their prediction intervals.
(Note that with monthly data it is actually sufficient just to show the next twelve months only)
After visual inspection of the plot, as well as the other graphs, I am confident that the predictions given for the Arctic
sea ice areas are going to be quite accurate and reliable. This is due to a number of reasons. Firstly it can be seen on the
plot that there is little variation in between the raw and fitted data indicating that the model produced is a good fit.
Secondly, as shown in the graphs, the seasonal trends are very regular and consistent from year to year and thirdly, the
residuals, or unpredictable elements are not significant and do not appear to contribute greatly to the variation in sea
ice areas.
Therefore I am going to predict that the area of sea ice in the Arctic in September 2011 is going to be between 1.89
million km2 and 4.05 million km2, while the area in September 2012 is going to fall between 1.13 million km2 and 4.86
million km2. It is important to note that caution is needed when extrapolating; especially when predicting further out
from the most recent data and this is indicated by the widening confidence limits for the second prediction.
Interestingly enough, when I compare the predicted Arctic sea ice areas to the actual data gathered from the internet, I
notice that while they fall within the prediction interval, they are actually lower than the fitted data predicted by the
Holt Winters model.
i.e. The Holt Winters model predicted a fitted sea ice area of 2.9704 million km2 for September 2011, whereas the
actual recorded area was less at approximately 2.92 million km2. When it came to September 2012, the model
predicted an area of 2.9917 million km2 whereas the actual data recorded was clearly less at approximately 2.2 million
km2. This would indicate that the Arctic sea ice areas are indeed decreasing in the trough months and that there could
be more unpredictable elements now contributing to the variation in the data. It also indicates that the predictions
calculated by the Holt Winters model were not as accurate as initially thought.
NOTE: Another way to determine the accuracy of a model is to redo the time series minus the final three data points
and then use the model to see how close the predictions calculated are to the actual raw data values originally given.
Relating to Other Time Series
Antarctic sea ice area:
From the above graphs it can be seen that unlike the Arctic sea ice areas, the Antarctic area appears to be remaining
relatively constant in terms of the long term trend. The level from the period of January 1990 to March 2011 has
remained at around 8.5 million km2
In terms of the seasonal patterns, the area of Antarctic sea ice areas has also remained very consistent. As expected,
since we are now dealing with the southern hemisphere, peak months are usually around September and average about
5.5 million km2 above the trend, whereas trough months are usually around February and average about 6.5 million
km2 below the trend.
As for the residuals, they are even smaller for the Antarctic sea ice areas and account for less than 5% of the variation.
Also, unlike the Arctic sea ice, the Antarctic has less variation in its residuals remains smoother throughout the entire
time series. In terms of contribution, the Antarctic also has the seasonal component contributing the most to the
variation at around 89%.
Historic Data (1979 to 1990):
As seen by the image on a previous page, the average Arctic sea ice area, while still regular in its seasonal pattern, was
clearly much greater when records first began and as such it has clearly decreased on a regular basis since 1979. This
decrease has occurred in throughout the entire season, although the decrease has appeared to be more pronounced
during the trough months.
Global Temperatures:
From the above graph it can clearly be seen that since 1880 the average global temperature has raised by almost a
whole degree Celsius. Of interest to me however is the data from around 1990 as when compared to the Arctic sea ice
areas, it can be seen that over the time that the sea ice area has been decreasing, the global temperatures have been
rising and also at what looks like the greatest rate over the last 100+ years of data. This would suggest that the rising of
global temperatures could be having an effect on Arctic sea ice areas.
Having that said, it was seen that over the same time period the Antarctic sea ice area has not decreased suggesting
that either there is something else that could be causing the sea ice in the Arctic to melt, or that the global warming
phenomenon is only affecting the ice regions in the Northern hemisphere. Either way, this clearly represents an
opportunity for further research. This research could either be to confirm whether or not the global warming
phenomenon is restricted to the Northern hemisphere or whether there is indeed something else, like CO2 emissions
causing the Arctic sea ice areas to melt as it has.
Conclusion
While appearing to remain fairly constant at the beginning of the time series, I feel that the Arctic sea ice areas have
gradually been declining since around 1996. While the predictions (which from many accounts appeared to be quite
reliable) showed that the sea ice areas would be remaining constant if not slightly increasing over 2011 to 2012, the
most recent data obtained showed that the areas indeed had continued to decrease.
When comparing it to average global temperatures, it seemed apparent that there could be a relationship between the
temperatures rising at the same time that the Arctic sea ice areas have been decreasing. However, when the Antarctic
sea ice areas were investigated it was clear that this had remained constant over the same time period which was not
what I would have expected.
This would suggest that there is opportunity for further research as I have already mentioned above by either looking
into whether the effect of global warming on the sea ice areas is indeed restricted to just the Northern hemisphere or
whether or not there is another phenomenon, such as the recently discussed CO2 emissions or the much reported ozone
depletion that could be causing the Arctic sea ice areas to continue decreasing as they have.
In terms of usefulness, I believe that my findings as well as the results of any further investigations could be of use to
environmental scientists who are studying the melting sea ice areas in the Arctic as well as ministers and Government
employees who are focused on the effects and subsequent laws related to global warming and emissions etc. Other
countries who could be affected by rising sea levels would also gain use from these findings as flooding and loss of
coastal land is becoming a focal point for a number of countries, especially the smaller island nations.