National Public Radio: This winter, many Brits have been shivering through their coldest cold snap in 30 years. Beijing’s residents witnessed their city’s biggest one-day snowfall in nearly 60 years. And on a flight from Dallas to Washington, D.C., an All Things Considered producer encountered a headwind strong enough to delay his plane. That’s uncommon, because the wind usually blows the other direction. So what’s behind all this unusual weather? According to Mark Serreze, it’s the …