“An unprecedented and worrying event”, confirmed Jean-Baptiste Sallée, oceanographer and climatologist at the National Centre for Scientific Research (CNRS) in France. “We are facing something unprecedented, with an iceberg that does not grow at a natural pace. The question is: have we entered a new regime? But it is still too early to answer,” he said. Until recently, the Antarctic ice sheet appeared to be spared the effects of global warming. For 35 years, it remained stable and even grew slightly, reaching a record of over 20 million square kilometres in September 2014 for the first time since 1979. “In 2015, everything turned upside down: we lost in 2-3 years what we won in 35 years”, said Francois Massonnet, climatologist at the Catholic University of Louvain, in Belgium. “Since 2016, we have broken records almost every year, and it seems that these records are not independent of each other,” he added. One hypothesis would be, according to Massonnet, that it would be a self-perpetuating phenomenon: the ocean warms more in the summer due to the lack of sea ice. Then, “when winter returns, first all the excess heat must be released before ice can form on the sea,” explained Massonnet. This thinner ice melts at a faster rate when summer returns. This retreat of the sea ice “is consistent with climate change that is beginning to have an impact on the Antarctic sea ice,” said Sallée. But researchers are reluctant to make a formal link to global warming because climate models have previously had difficulty predicting changes in Antarctic sea ice. What is known, however, is that the reduction of sea ice risks aggravating global warming. The ocean, which is darker in colour, reflects less of the sun’s rays compared to white ice and therefore stores more heat. As it melts, the ice sheet also loses its role as a buffer between the waves and the Antarctic ice sheet, accelerating the outflow of freshwater glaciers into the ocean. In addition, the retreat of the sea ice threatens the rich ecosystem that it shelters. Far from being an expanse of ice, “the ice pack forms terraces, tunnels, and labyrinths, being a refuge area for living things that can hide from such predators”, explained Sara Labrousse, a researcher specialized in polar ecology at CNRS. The ice shelf is especially home to krill, shrimp-like crustaceans that are the food of many predators such as whales, seals, and penguins. “The shoal is also a resting, moulting, and breeding area for many mammals and seabirds,” added Sara Labrousse. When the ice breaks too early in the season, young seals that have little fat and insufficiently waterproof fur can die of hypothermia after falling into the water, the researcher said. The retreat of the ice sheet “may endanger populations”, she warned.

By Roxana Stanica