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Researchers at the UK Health Security Agency analysed data on 51,281 people who tested positive for Omicron or Delta between 5 and 11 December 2021 and their 151,592 close contacts. They found that whereas people infected with Delta spread the infection to roughly 11% of their household members, those who had Omicron spread it to almost 16% .
The record low was partly due to strong winds pushing ice out of the Ross Sea, a bay off the coast of Antarctica, to areas farther north, where it is warmer. There, the ice broke up and melted, says Walt Meier, a senior research scientist at NSIDC, who is based at the University of Colorado Boulder. “I think much, if not all, of the event can be ascribed to natural variability,” says Meier.
Unlike in the Arctic, where sea ice has declined rapidly since satellite measurements began, Antarctic sea ice has seen a lot of year-to-year variability — contradicting expectations raised by some climate models that predicted it should decline in response to increased greenhouse-gas emissions. “With so much variability, it is not too surprising that one could get a record low,” says Meier.