The US president, Joe Biden, and Canadian prime minister, Justin Trudeau, have warned worried populations to brace for more.
Shocked climate scientists are wondering how even worst-case scenarios failed to predict such furnace-like conditions so far north.
Trapped in a vast heat dome that enveloped western Canada and the north-western US, temperatures had nowhere to go but up.
In Lytton, the Canadian national heat record was broken on Monday, smashed on Tuesday and then obliterated on Wednesday when the local monitoring station registered 49.6C (121F).
The previous week, northern Europe and Russia also sweltered in an unprecedented heat bubble.
“In the present-day climate, getting an extremely hot June is common and is likely to occur twice in three decades.
Climate models capture this effect very well and predict large increases in heat extremes. »