On top of the maps contours are drawn indicating the confidence of the statistics (larger is better). Since the sea ice does not retreat and expand completely every year, not all areas experience the same number of freeze-ups and break-ups over an equal period of years. Therefore, some areas may experience relatively few freeze-ups and break-ups, thus reducing the confidence in the statistics of the area. This is illustrated by the contours overlayed the plots, indicating the percentage of years the statistic was able to be estimated from. In addition, only areas having more than 6 samples are considered for statistical robustness.

Click here to change between the full period and the wmo standard climate period.