The heat wave baking the U.S. Pacific Northwest and British Columbia, Canada, is of an intensity never recorded by modern humans. By one measure it is more rare than a once in a 1,000 year event — which means that if you could live in this particular spot for 1,000 years, you'd likely only experience a heat dome like this once, if ever.
Portland, Oregon, has already broken its all-time record hottest temperature at 108 degrees on Saturday and the peak of the heat wave has not even been reached yet. Canada is expected to register the nation's all-time highest temperature before the event is done. These are extremely dangerous numbers, especially in a region not used to heat like this, where many people do not have air conditioning.