Global temperatures hit a record on Monday, underscoring the dangers of ever-increasing carbon emissions generated from burning fossil fuels.

The average worldwide temperature was 17C (63F), just above the previous record of 16.9C reached in August 2016, according to data from the National Centers for Environmental Prediction. The new high underscores the extremity of 2023’s summer in the northern hemisphere.

“This is not a milestone we should be celebrating, it’s a death sentence for people and ecosystems,” said Friederike Otto, a senior lecturer at the Grantham Institute for Climate Change and the Environment. “Worryingly, it won’t be the hottest day for a long time.” The El Niño weather phenomenon is set to break more records this year, she said.

The heat this summer has already put millions of people around the world at risk. China is experiencing its latest scorching heat wave less than two weeks after temperatures broke records in Beijing. Extreme heat in India last month has been linked to deaths in some of its poorest regions. Last week saw a dangerous heat dome cover Texas and northern Mexico, while the UK baked in its hottest June on record.