claim: Arctic sea ice has been steadily thinning, even in the last few years while the surface ice (eg - sea ice extent) increased slightly.
evidence: Since the last glacial maximum about 20,000 years ago, the sea level has risen by more than 125 metres (410 ft), with rates varying from less than a mm/year to 40+ mm/year, as a result of melting ice sheets over Canada and Eurasia.