China’s most populous city, Shanghai, has issued its highest alert for extreme heat for the third time this summer as sweltering temperatures repeatedly tested records this week. The commercial and industrial hub of 25 million people declared a red alert on Thursday, warning of expected temperatures of at least 40C (104F) in the next 24 hours. Temperatures soared as high as 40.6 C in the afternoon but fell short of Wednesday’s 40.9 C, which matched a 2017 record. Extreme heat conditions have also taken hold in parts of Europe. Firefighters…