Isn't ice building up in some places, like Antarctica (and doesn't that offset losses in the Arctic)?

As the amount of summertime ice has declined in the Arctic Ocean, it has increased in the Southern Ocean adjoining Antarctica.  The processes controlling ice in these two areas are not the same, though, and the implications for global climate are very different.

Southern sea ice forms and decays each year around the edge of Antarctica.  However, the continent itself remains virtually covered with ice year round. In the Arctic Ocean, there is about twice as much summer ice as there is around Antarctica. The loss of summer ice in the Arctic threatens to expose much of the ocean to the midsummer sun. Since dark ocean absorbs far more sunlight than does the brighter sea ice, this leads to a warmer ocean and, thus, further melting, in a warming feedback loop. The total loss of summer sea ice in the Arctic would also have profound implications for the people and wildlife of this region.