http://www.bbc.co.uk/news/science-environment-22271972
The earliest satellite maps of Arctic and Antarctic sea-ice have been assembled by scientists.

They were made using data from Nasa’s Nimbus-1 spacecraft, which was launched in 1964 to test new technologies for imaging weather systems from orbit.

The satellite’s old pictures have now been re-analysed to determine the extent of the marine ice at the poles in the September of that year.
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Interesting results but sounds like very tedious work.

Antarctic is possibly in the range of natural variability, so the same may apply to the Arctic?