Antarctica's cracking ice sheet is part of a process that could reshape the world

The first summer without an Arctic ice sheet is already on the horizon. The massive chunk of frozen ocean has capped the northern pole of our planet year-round for millennia, but it's now at risk of receding until it disappears entirely.

Unlike its northern sibling, the kilometers-thick Antarctic ice cap in the south is seated on a buried continent rather than on water. It's bigger and older than the Arctic ice sheet, and less vulnerable to threats of a warming climate.

Researchers generally agree, however, that the Antarctic will also lose significant amounts of ice mass as the Earth's temperature rises. The timeline and extent of that loss is just less clear. Unlike the charts of the Arctic's annual ice, which seem to have taken a plunge toward zero over the last decade, the Antarctic's process has been more wobbly. As recently as 2014, the southern ice cap reached is largest extent on record.

Here's what we know about Antarctica's strange, ancient ice, and what could happen in its future.