Global warming is melting Antarctic ice from below

Global warming is melting Antarctic ice from below

John Abraham
Wed 9 May 2018 06.00 EDT

•••••

In the Arctic, almost all the ice is floating on water – there is very little land. So, we talk about ‘sea ice’ in the north, formed from frozen sea water. On the other hand, Antarctica is a massive land mass that is covered by ice formed from snowfall (called an ‘ice sheet’). There is some floating ice around the perimeter of the land, but the vast majority of Antarctic ice is on land.

This difference not only affects how these regions response to climate change, but it also impacts their importance. We know that when floating ice melts, the ocean levels will not rise, because the ice was already floating in the water. But, when land ice melts, the liquid water flows into the ocean and causes the water levels to rise. So, at least from a sea-level perspective, land ice is more important than floating ice.

There are other differences between the north and south. One feature of the south is that there is a strong current that travels around Antarctica and partially shields it from waters elsewhere in the ocean. The Nasa Jet Propulsion Laboratory provides a good summary of some of the differences between the poles.
Advertisement

With global warming, both of the poles are warming quite quickly, and this warming is causing ice to melt in both regions. When we think of ice melting, we may think of it melting from above, as the ice is heated from the air, from sunlight, or from infrared energy from the atmosphere. But in truth, a lot of the melting comes from below. For instance, in the Antarctic, the ice shelves extend from the land out over the water. The bottom of the ice shelf is exposed to the ocean. If the ocean warms up, it can melt the underside of the shelf and cause it to thin or break off into the ocean.

•••••

Around Antarctica, water at the ocean surface cools down and becomes saltier. These combined effects make the surface waters sink down to the sea floor. But as ice melt increases, fresh water flows into the ocean and interrupts this buoyancy effect. This “freshening” of the water can slow down or shut down the vertical mixing of the ocean. When this happens, the cold waters at the surface cannot sink. The deeper waters retain their heat and melt the ice from below.

•••••