The Double Heat Dome

Five years ago, summer in Lytton, British Columbia, became “a living hell.” Temperatures climbed to nearly 50°C in late June, the highest figure recorded in Canada, and a wildfire spread into the town in early July. Ninety percent of Lytton burned, forcing about 250 residents to evacuate.

That disaster followed the formation of a vast heat dome over western Canada and the northwestern United States. Heat domes develop when strong, hot high pressure settles over a region while heat flows in from the Pacific or Africa. The pattern that produced the sweltering conditions on the Korean Peninsula was different: two high-pressure systems formed a “double heat dome.”

A hot, dry Tibetan high-pressure system remained nearly stationary about 10 kilometers above the ground. Around five kilometers lower, a hot and humid North Pacific high-pressure system continued expanding toward the peninsula. Together, they pressed down like two pot lids, preventing heat rising from the surface from escaping and allowing temperatures inside the system to build.

The column links the pattern to the jet stream, which normally pushes the Tibetan high northeastward or back toward Tibet. Rising summer temperatures in the Arctic have reduced the temperature gap with the equatorial region, weakening the jet stream. That is why global warming is being cited as one factor behind the heat dome.

The same system has also acted as a barrier against typhoons. None of the 23 typhoons this year, including “Wandering,” which recently dissipated off Japan, made landfall on the Korean Peninsula. Meteorologists say the heat dome is changing typhoon paths or causing storms to weaken early. Yet typhoons also replenish agricultural and household water supplies and oxygenate coastal waters. The column argues that the benefits and harms of blocking them are difficult to measure, while the unpredictable reach of human-driven weather changes is plainly worrying.