Update: In an earlier version the legend on the graph had blue labeled as Antarctic even though it was Arctic. The body of the post had it right (thanks Tom,Hugh,Tom,Anthony,Mike and Sundance for noticing ).
The green is the AMO – Atlantic Multidecadal Oscillation. The red is Antarctic Sea Ice Extent. The blue is the Arctic Sea Ice Extent.
The dashed lines are the liner trends for each.
There are three amazing things:
1) The AMO trend is identical to the Antarctic trend even though the AMO is the sea surface trend of the North Atlantic Ocean! The trend are so close it is hard to see the AMO and Antarctic trends as separate items.
2) The Arctic trend is almost a mirror image of the Antarctic trend.
3) The cross over point is around 1997 which is when the AMO went officially positive (it sometimes goes opposite to the main trend for a few months)
The AMO is cyclic and will return to negative soon enough and this graph implies that sea ice trends will just reverse in a few years.
Click on the graph for a larger size.