This week, many people who live in the U.S. have woken up to hazy skies. Wildfire smoke from Eastern Canada continues to trail down the East Coast and as far west as Minnesota. State and local authorities have issued air-quality warnings throughout the affected regions, and it could be days before they’re lifted. Wildfire pollution may be a new threat to some of these regions, but with global temperatures climbing, it could be more common in the future.