The cold weather is localised to parts of the mid to upper northern hemisphere – the rest of the world isn’t experiencing these same conditions (as indicated by Dawei’s link). Globally it’s the hottest it’s ever been.
What we’re experiencing is a short term weather event that started on 17th-18th December and will last another 10 to 14 days. It’s caused by an area of high pressure over the Arctic which is feeding cold air into much of the US, parts of Canada, Northern Europe, parts of Russia and parts of China – and nowhere else.
It’s a cyclical event with a periodicity of approx 16 years. If it hadn’t happened this year it would have happened in 1 or 2 years time. It’s next due to occur in 2025 (give or take a year).
In the larger scheme of things you’re looking at 3 weeks out of 150 years, clearly no conclusions can be drawn from such a short timeframe.