“What the researchers didn’t expect were ‘enormous holes’ in the [Arctic] sea ice…. ‘We can’t explain them yet,… And the Antarctic blew us away.’ ”
via Nimbus data rescue.
Nor is the current satellite record, dating only to the late 1970s, enough to cover a single entire sea-ice cycle which can take roughly 60 years to complete, in conjunction with the other oceanic temperature cycles such as the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO).
When you hear the words “in recorded history” appended to a claim about climate change, it is important to remember that our recorded history for most elements of the climate is very limited. Even truly-global air temperature measurements by satellites began only in late 1978. Global ocean heat content measurements began only in the 2000s (and still, it’s only to a depth of 3000 meters–we have no real clue as to what’s going on below that depth in any reliable way), and excludes areas in the ocean covered by sea ice such as the Arctic and Antarctic.
The earth’s climate system is, and always has been, in a constant state of change. So are the data available to measure that climate system.