We mentioned recently the rebound in Arctic ice levels compared to those found at the end of last summer; now that the 2013 minimum has been reached, Forbes' Alex Knapp points out that 2013's figures still show the 6th lowest ice extent in recorded history. "This pattern is expected to continue as average global temperatures continue to rise, leading to further Arctic Ice melts. The volume of sea ice – that is, how thick the Arctic ice is, has also been steadily declining over the same period. And although the charts above only go back to the 80s, the loss of sea ice began several decades prior to that. In 2011, a paper published in Nature estimating Arctic ice extent for the past 1450 years shows a sharp decline in Arctic ice beginning in the mid-20th century."