Arctic Sea Ice Time Series Report Exemplar

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.

Some scientists have gone so far as to predict an ice free Arctic. This is a quote from a scientific article by E. Hansen.

“When this condition is met, conditions favorable to melt could lead to a nearly ice free Arctic Ocean during summer. With winter old ice modal thicknesses close to 2.0 m, we are very close to crossing this threshold. As such, the record low sea ice extents observed in 2007 and 2012 are mere manifestations of the thin old level ice. The scenario of a nearly ice free Arctic Ocean seems closer than ever.” E. Hansen 2013.

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 and see if we can predict future sea ice levels in the arctic.

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 and about 4000 km2 per month over the whole time period. If we just look at the period since January 1997 there is a fall of about 6250 km 2 per month. 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% as most are well under 1.1 million km2. 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 Approx % (million km2) Contribution Raw data 3 11 14 Trend 8.5 9.5 1 1/11 x 100 = 9% Seasonal -5 4 9 9/11 x 100 = 82% Residual -1 1 2 Note that these are ball-park figures taken from the iNZight plots 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 fairly 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 CO 2 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.