Reuters: While much of the Northern Hemisphere has shivered in a cold snap in recent weeks, temperatures in the Arctic soared to unusually high levels, U.S. scientists reported. This strange atmospheric pattern is caused by natural variability and not by rising levels of greenhouse gases. However, it could affect Arctic ice which in turn may impact global warming, said Mark Serreze, director of the U.S. National Snow and Ice Data Center in Colorado. “It’s very warm over the Arctic, with …