Record-breaking heat wave hits Pacific Northwest with millions under advisory.

More than 12 million people in the Pacific Northwest are under a heat advisory as temperatures are expected to climb nearly 20 degrees higher than normal due to a "heat dome" caused by an abnormal area of high pressure. The extreme weather is also extending into Canada, where wildfires are raging. Climate change has increased the likelihood of such extreme heat waves, which are becoming hotter, longer, and more frequent around the world.