[southern_cross]

Given that most of the "really cold" places are well below freezing, then any warming from "well below freezing" to "a little bit less well below freezing" means that most of the snow and ice (maybe pretty much all of it) still stays frozen. And what does melt may just quickly refreeze pretty much in place when temps drop again, as they usually do. So there's that.

Also, in the oceans salt water has to get to at least a couple of degrees below zero C before it actually freezes, at which point it turns into freshwater ice as it expels its salt. But then that freshwater ice has to warm back up to at least zero C before it melts again, leading to a small but real "anti-melting" bias. So there's that.

Also, floating ice actually increases in density (decreases in volume) as it melts and turns to water. I forget the exact numbers, but it has to warm by several degrees above freezing before it expands to the point where it actually takes up more volume that the frozen/not-quite-frozen variety. This leads to small but real "anti-expansion" bias. So there's that.

Fun stuff, huh?