Question: If you don't know how thick the Arctic ice is, isn't it difficult to accurately calculate its volume?

NASA Lead Scientist Determines A Trend From One Point | Real Science

“In 2009 for the first time, we were able to figure out (from satellites) what the thickness of the Arctic ice was – and we are finding that it is thinner now.”

Polar Science Center » Arctic Sea Ice Volume Anomaly, version 2

The blue line represents the trend calculated from January 1 1979 to the most recent date indicated on the figure.