The largest uncertainties in future sea-level rise contributions come from the polar ice sheets. With most ice lost from Antarctica through ocean driven melting at the base of its ice shelves (basal melt), ocean warming will play a primary role in determining the future behaviour of the Antarctic Ice Sheet. While retreating and thinning ice shelves do not directly increase sea level, the ice shelves are less able to protect and buttress the ice sheet, triggering a dynamic response in the ice sheet. It is now believed this could occur more rapidly than previously though adding urgency to the need to understand how the ocean influences ice sheet stability.
Melt of glacial ice, in the form of icebergs or floating ice shelves and glacier tongues, also makes an important contribution to the high-latitude freshwater balance. Interest in ice shelf basal melt has increased with growing evidence that the continental ice sheets can respond rapidly to changes in the floating ice shelves that acts as a buttress to inhibit the flow of ice to the sea. For example, the rapid collapse of the Larsen-B ice shelf was followed by a dramatic acceleration of the flow of glaciers feeding the ice shelf area If the ice sheets respond rapidly to changes in the floating ice, present estimates of the rate of future sea-level rise may be too conservative. Warmer ocean temperatures have been linked to an increase in the basal melt rate and the retreat of grounding lines in Antarctica, with a 1°C increase in ocean temperatures increases basal melt rates by ~10 m yr-1.
The dynamic response of the ice sheets will be determined largely by what happens in the ocean, as air temperatures over the Antarctic continent are unlikely to increase enough to cause widespread surface melting, unlike Greenland. Reducing the uncertainty in future estimates of sea-level rise requires observations of changes in ocean temperature and circulation and an improved understanding of both how warm water is transferred from the deep ocean to the cavity under the ice shelf and ocean-ice shelf interaction. Ice shelves are just beginning to be added to climate models, but the ice shelf melt rates depends strongly on oceanic properties and circulation under the ice shelf both of which are not well-represented in present models; hence long-term observations of the ocean near and beneath ice shelves are crucial for testing and improving models.