The summer of 2023 was hotter than any other in the Northern Hemisphere for the past two millennia.
Scientists previously determined that 2023 was the hottest year since 1850, when global modern temperature records began.
The extreme warmth of last summer not only smashed modern records but also exceeded the warmest summer prior to the instrumental record - in the year 246 - by more than half a degree Celsius.
It was almost 4C warmer than the coldest summer (in 536).
European Union's Copernicus Climate Change Service were saying the year of 2023 was "very likely" to have been the warmest in some 100,000 years.
More than 150,000 deaths in 43 countries linked to heatwaves for each year between 1990 and 2019.