Thanks for reading the dispatch. Understanding the variability in a data set is indeed critical when describing trends. Throughout most of June 2009, ice extent fell about 2 standard deviations below the 1979-2000 mean. The chart that is presented above, but with standard deviations indicated by gray shading, can be found at http://nsidc.org/images/arcticseaicenews/20090706_Figure2.png. During April and May, the ice extent was below the 1979-2000 mean, but usually within 2 standard deviations of the mean.

Even better than visualizing the variability is examining the full data set. The website The Cryosphere Today provides a graph of ice extent anomaly from the 1979-2000 average, for the entire data set from 1979 to today. Following the graph from left to right, the downward trend is apparent. The graph is available from their main website http://arctic.atmos.uiuc.edu/cryosphere/ where it is titled “Tale of the Tape”, or here at http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg.

Variability in the data can also be described by testing for significance of trends. Meier et al. (2007) (see the citation above) tested for significant trends in the 1979-2006 satellite data of ice extent. They found that ice extent exhibited a significant decline in every month of the year, with the most dramatic declines occurring in summer months. The significance testing used an F test with a 99% confidence level and a null hypothesis of a zero trend. It is worth noting that the decline in ice is significant across the Arctic, but it is heterogeneous in space and time. Some regions of the Arctic are experiencing dramatic loss while other areas are experiencing little or no loss. I encourage you to read their paper for a detailed description.

Otherwise…you ain’t got jack.