Glaciers are the ‘canary in the coal mine’. Shrinking glaciers are the world’s most visual, most impressive evidence of globally warming temperatures. This is particularly evident around the Antarctic Peninsula, which is currently warming at around six times the global average. This warming is driving dramatic changes in snow and ice cover; glaciers are thinning, accelerating and receding, and their buttressing ice shelves are collapsing.
The Antarctic PeninsulaThe ~400 glaciers around the Antarctic Peninsula are particularly sensitive to climate change because they are relatively small and are located on a high mountainous spine, projecting northwards from the Antarctic continent towards warmer latitudes. Although the ice sheet here would only raise global sea levels by 0.2 m on full melting, it is the most responsive and most rapidly changing of all the ice sheets in Antarctica. These small, steep outlet glaciers have fast response times, so changes in their environmental conditions are quickly reflected in their length and volume. Repeated satellite imagery has shown that 87% of the glaciers around the Antarctic Peninsula have been receding for decades. The lower parts of tidewater glaciers, which end in the ocean, are thinning as they are melted by warm ocean waters encroaching onto the continental shelf. Measurements of 300 glaciers on the Antarctic Peninsula showed that they are accelerating in response to this frontal thinning, directly contributing to sea level rise at an ever increasing rate.
Ice shelves are the floating extensions of grounded glaciers. They fringe 75% of Antarctica’s coastline and collect 20% of Antarctica’s snowfall over 11% of its area. They melt from below, and calve icebergs into the ocean. Melting ice shelves do not contribute directly to sea level rise, because they’re already floating, but they do play an important role in ice dynamics. This is because ice shelves stabilise the grounded glaciers. When they are abruptly removed, the equilibrium is disrupted and the glacier must adapt to its new conditions. This means that the glaciers recede, thin and accelerate upon ice shelf collapse – all of which contribute ice to the world’s ocean and results in sea level rise. Several ice shelves on the northern Peninsula have already collapsed [video], resulting in dramatic glacier readjustment, which is still continuing 25 years after ice-shelf removal. The remaining, more southerly ice shelves around the Pacific sector of the Antarctic Peninsula are melting very rapidly at their base. Their thinning renders them vulnerable. During warm summer seasons, meltwater ponds on their surface, melting downwards and weakening the ice shelves structurally. Computer simulations predict that more ice shelves around the Antarctic Peninsula will collapse over the next few decades.
The West Antarctic Ice Sheet
Unlike the Antarctic Peninsula, the West Antarctic Ice Sheet is a massive ice sheet, capable of rising global sea levels by up to 3.3 m. What is concerning is that the West Antarctic Ice Sheet is currently exhibiting some rapid changes. Pine Island Glacier is one of the largest ice streams in Antarctica, with a 1.5 m sea-level-equivalent of ice. It is buttressed by a large ice shelf, and the ice stream itself rests on ground that is up to 2000 m below sea level, and it gets deeper further inland. That makes the ice stream vulnerable to melting at its base by warm ocean waters. Pine Island Glacier is currently accelerating, thinning and receding, and if the stabilising ice shelf collapses, could dramatically raise global sea levels within a few centuries.
The East Antarctic Ice Sheet
The East Antarctic Ice Sheet is the behemoth of Antarctica, with enough ice to raise global sea levels by 53 m on full melting. The East Antarctic Ice Sheet is a massive, 3000 m thick ice sheet, largely grounded above sea level (and so more stable than West Antarctica). It is the location of the South Pole, and it is the coldest, highest and driest of all the ice sheets. Little warming is currently observed over East Antarctica, and it has a slightly positive mass balance; that is, it is growing slightly. However, it is not growing enough to offset losses from West Antarctica and the Antarctic Peninsula. The outlet glaciers fringing the East Antarctic Ice Sheet are also currently fluctuating and receding, suggesting that they be more sensitive to climate change than previously thought. Computer simulations suggest that global warming will result in increased snowfall over Antarctica, but this may just cause glacier acceleration rather than glacier growth, and will still be insufficient to offset the massive losses expected elsewhere in Antarctica.