Warming of the Arctic caused by climate change has increased the number of polar vortex outbreaks, when frigid air from the far north bathes the central and eastern United States in killer cold, a study finds.

The study in the journal Science Thursday is the first to show the connections between changes in the polar region and February's Valentine's Week freeze that triggered widespread power outages in Texas, killing more than 170 people and causing at least $20 billion in damage.

The polar vortex normally keeps icy air trapped in the Arctic. But warmer air weakens the vortex, allowing it to...