The summer of 2023 was the hottest in the northern hemisphere in the past 2,000 years, researchers have found. It was almost four degrees warmer than the coldest summer during the same period. Last year was reported as the hottest year on record, but instrumental evidence only reaches back as far as 1850 at best – and most records are limited to certain regions. Now scientists from the University of Cambridge and the Johannes Gutenberg University Mainz have used past climate information from annually resolved tree rings over two millennia to show how exceptional the summer of 2023 was. Even al…