A wave of predictions that a polar vortex will make this January the coldest in years sent natural gas prices up this week, and experts say it could test supplies in the U.S. and Europe.

Natural gas prices have surged nearly 25% over the last month. Energy experts attribute the rise to cold weather expected in January and geopolitical issues around the globe. The cold temperatures could make the month one of the coldest Januarys in over a decade.