Turns out it's the little things we need to worry about in climate change. When they're in trouble, a great polar ecosystem may be, too.

The oceans are now absorbing so much carbon dioxide they are acidifying at an unprecedented rate, according to the International Program on the State of the Ocean.

Antarctic krill are under threat. Credit:Australian Antarctic Division

Geological records show the current acidification is unparalleled in at least the past 300 million years, IPSO's latest State of the Ocean report says.

''We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure,'' it says.