When attempting to visualize a time series, it is often helpful to plot the data as a scatterplot with lines connecting the points. A good example of this is the sea ice extent graph on Cryosphere Today. It shows five time series all plotted on the same graph. This gives a user a lot of information in just one graphic. But by choosing this particular graph style, it can lead to confusion. A graph that is even more confusing is their ice area graph. This includes the annual cycle, which makes it nearly impossible for an average user to even tell if the ice area is decreasing.

They do offer a hemispheric anomaly figure which is much better, but it can still be misused/abused. For instance, the current anomaly is smal compared to the recent past. In fact, if one was so inclined, I could say that the sea ice anomaly is the same today as it was in 1980. Cherrypicking? Sure. But it’s happened before.

I’m going to look at sea ice extent plots. But instead of scatterplots, I’m going to use colored bar charts. The colors will be used to represent which quintile the particular data point fall in. I’ll use the ’standard’ colors where blues will represent colder temperatures and reds will represent warmer temperatures.

The spring sea ice extent is shown above and it’s clearly visible that the last 25 years or so have had the smallest amounts of ice. All of the red bars are located within the last 30 years and there are no “nomal” (green) or “above normal” (blue or purple) ice extents during this time.

The summer sea ice extent shows the same general pattern as the spring graph. However, the vertical axis spans a much larger range.

The autumn pattern is a little different than the summer and spring. There isn’t the large anomaly in the 1940s, and the distribution of ice extents before 1970 are fairly even except for the smallest values. That is, there is about the same number of oranges, greens, blues, and purples. The last few years are all in the red though.

The winter time series is the most unlike the others. Not all of the red bars represent recent years. There are 3 years before 1970 that are in the lowest quintile for ice extent. There are also 3 years in the last 10 that are in the 4th quintile (blue).

The annual sea ice extent is like the summer and spring figures. Most of the large ice extents are in the early years, and most of the small ice extents are in the later years.

This is the same information that is available on the Cryosphere Today website. However, by separating the months and using color to denote the quintiles, I believe that it is easier to interprete that the degree to which we are losing sea ice.

All plots derived from data from Cryosphere Today.

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