The week began with a biting cold snap that hammered much of the U.S., the product of a jet stream that slips out of its usual path more often these days. Then came the catastrophe of rampant and deadly wildfires in a California desiccated by extreme drought. And then the capper: meteorologists on Friday confirmed that 2024 was the hottest year on record. Scientists say the week’s extreme weather is one of the hallmarks of climate change. By Melina Walling.