In early January the high atmosphere above the Arctic warmed abruptly, which happens about six times a decade. That warming gradually weakened the jet stream below, causing frigid air to spill down across North America. Texas froze, and tragedy ensued. Some evidence points to a link between the quickly heating Arctic and cold spells to the south, but not everyone agrees, and it’s become a bit of a stalemate. Two things are certain: Winter is the fastest-warming season, and Texas missed warnings.
Scientists are much clearer about humanity’s role in more common extreme weather events. Some 40,000 people evacuated their homes in New South Wales in March after biblical rainfall. Aspects of Australia’s climate make parsing the climate influence of any precipitation event more complicated, but new work affirms that more greenhouse gas means more heat, a wetter atmosphere, and more extreme rainfall. It’s not only about more or less precipitation—the timing of the seasons is changing almost everywhere, with California’s rainy season now starting a month later than it did 60 years ago.