Not sat data...the other data was gathered by ships and coastal observations and thus is like comparing apples to oranges.
I am aware that the data is not satellite data; but going back to the 1950s at least, ice extent was estimated by aerial survey. Going back further than that, ship and coastal surveys provide the data. How would you argue that such observations are so flawed that they do not provide a reasonably accurate indication of sea ice extent?
I offer the following references for your examination. If you have problems with the methodologies, explain what they are.
Global Warming and Northern Hemisphere Sea Ice Extent
The key reference is 13, by Chapman and Walsh. Here's their Web site:
Arctic Climate Research at the University of Illinois
The data is online and Dr. Chapman invites anyone with questions about it to contact him by email. Why don't you email him and discuss how the data quality of the observational archive compares with the more recent satellite data?
Here is the documentation page for the sea ice data. I recommend reading the "Expert User Guidance" section:
Walsh and Chapman Northern Hemisphere Sea Ice Data Set
dangus, there are a couple of nice papers out there reporting that increased Antarctic sea ice is a consequence of global warming. I've posted the links to them before and I'm a tad lazy today. Google works to find them.