Scientists call it Santa’s revenge. It’s the theory that persistent weather patterns at the mid-latitudes – like this winter’s tediously long-lasting polar vortex or California’s severe drought – are a direct consequence of climate change heating up the Arctic. New evidence suggests the link is real, even as experts continue to argue over how much it is influencing the weather on a day to day basis. The effect has implications for severe weather predictions, food security and water use across the northern hemisphere. If the data are right, they suggest that climate change in the Arctic is coming home to roost in a big and expensive way.