A record-breaking heatwave spread from the U.S. Mountain West to the East and into Canada on July 14 local time, with more than 100 million people under heat advisories. Hot, dry weather has fueled wildfires in southwestern Ontario, Canada, and northern Minnesota, USA. Over the next few days, air quality in the U.S. Midwest and Northeast is expected to be affected.

On July 9, in Phoenix, Arizona, a man was walking down the street. On that day, the highest temperature in Phoenix, Arizona, reached 45 degrees Celsius. 

Temperatures in many parts of the United States are expected to rise to between 32 and 37 degrees Celsius in the coming days, with some areas nearing 38 degrees Celsius. Ottawa and Toronto in Canada are forecast to reach a high of 38 degrees Celsius on the 14th. Canada’s Environment and Climate Change Department stated that hot, humid air could degrade air quality, with the Air Quality Health Index potentially approaching high-risk levels.

U.S. weather authorities forecast a slight drop in temperatures this weekend, but the “heat dome” is expected to persist over the Western mountain regions. A “heat dome” refers to a persistent ridge of high pressure in the upper atmosphere that, together with nearby low-pressure systems, forms an “Ω‑shaped” circulation pattern. This configuration traps hot air within a region, inhibiting the influx of cooler air and causing temperatures to rise continuously, thereby triggering extreme heat waves.

In addition, the UK Met Office released its annual report on the 15th, noting that extreme weather events are becoming increasingly frequent in the United Kingdom. Compared with the last century, the UK’s climate has undergone significant changes, with temperatures continuing to rise and an increase in extreme weather events. The number of days when London’s temperature exceeds 30 degrees Celsius has tripled compared with the 1980s. Last year was the hottest on record for the United Kingdom.

The report indicates that since the 1980s, temperatures in the United Kingdom have risen by approximately 0.25 degrees Celsius per decade, with all regions affected. Taking southeastern England, where London is located, as an example, the temperature on the hottest day is 4.5 degrees Celsius higher than in the past. The reach of the heatwave has expanded northward, extending into high-altitude mountainous regions.