Perhaps things would be clearer if you where not referring to a Fall graph but posting a Winter Graph

This is the Fall graph.

http://climate.rutgers.edu/snowcover/ima...

I don't know but if the world is warmer, then you would think there would be less in spring. But you would also think the same for all the seasons. Perhaps there is more evaporation now so more snowfall? It's just a guess though.

ice extent increases in winter and melts in summer

However ice area doesn't dictate ice volume and both Arctic and Antarctic are losing more volume yearly

The seasons.

summer

be increasing in the fall

http://climate.rutgers.edu/snowcover/images/nhland_season1.png

But is decreasing in the spring

http://climate.rutgers.edu/snowcover/images/nhland_season2.png

Any ideas?