An international consortium of scientists has announced that ice losses from Antarctica have tripled in the last five years. Recent ice losses mean that sea levels are now rising faster than at any time in the past 25 years. Between 2012 and 2017, the continent lost 219 billion tonnes of ice per year, contributing 0.6mm per year to global sea level. Prior to 2012, Antarctica was losing ice at a steady rate of 76 billion tonnes per year (a 0.2mm per year sea level contribution).
The steep increase in ice loss has been driven by changes across Antarctica. The biggest change has been in West Antarctica where ice loss has risen from 53 billion tonnes per year in the 1990s to 159 billion tonnes per year since 2012. The ice is mostly coming off the huge Pine Island and Thwaites glaciers, which are being undermined by the warming of surrounding ocean waters. Ice shelf collapse at the Antarctic Peninsula, where air temperatures have risen sharply, has led to a further 25 billion tonnes per year increase in ice loss since the early 2000s. In East Antarctica, where the ice sheet has changed little over the past 25 years, ice accumulation now appears to be falling, tipping the mass balance towards decline.
The study, published in Nature, provides the most complete picture of Antarctic ice sheet change so far. The researchers combined data from 24 satellite surveys to produce the assessment of how and why Antarctica’s glaciers, ice shelves, and sea ice are changing. Satellites provide the best way to survey Antarctica’s changing ice cover, allowing scientists to track the extent, age, motion, and thickness of the ice.
The acceleration in ice loss has important implications for future sea levels. While Antarctica appeared to be tracking the lower range of IPCC sea level projections prior to 2012, this latest update suggests that it is in fact tracking the upper range after all – which allows for an additional 15cm rise in mean global sea level by 2100.
In another paper published in the same issue of Nature, a second group of researchers considered the future of Antarctica by looking at two scenarios for 2070. Under a high emission/low regulation scenario (+2.9°C rise in global air temperature), Antarctic ice loss is dramatic, leading to a marked acceleration in global sea level rise by 2070, threatening the world’s coastal regions. The continent is tipped into state where the accumulation of ice through snowfall on the continent is no longer enough to compensate for ice loss at the margins. A failure to effectively regulate tourism and resource interests will drive further changes to the continent. In contrast, the low emission/high regulation scenario (+0.9°C rise in global air temperature) sees Antarctica remain relatively unchanged.
How Antarctica’s future unfolds depends mostly on the choices that governments make over the next decade. However, as the latest assessment of Antarctica shows, presently, the world is headed toward the worst-case scenario, not the best-case.