http://neven1.typepad.com/.a/6a0133f03a1e37970b01b7c955fe52970b-800wi

The “anomaly” is the difference between the sea ice volume and the mean sea ice volume for that month over the last 38 years. The curve is noisy and the error bars are big, but the blue regression line trend is clear.

Sea ice volume cannot be measured directly, but must be modeled with data from a variety of sensors using an algorithm incorporating many assumptions, so it is not as robust a metric as surface area or ice extent, which can be measured directly off satellite imagery. But even if we assume there are substantial systematic errors in this figure, the trend is still unmistakable. We are losing Arctic sea ice volume at the rate of roughly 300 cubic kilometers/year.