At the time of the IPCC AR5, very few scientific studies relevant to the impacts of global warming of 1.5℃ above pre-industrial levels were available. In 2018, the IPCC concluded a Special Report on the impacts of global warming of 1.5℃ levels and related global GHG emission pathways, following an invitation expressed in the Decision text of the Paris Agreement . The report assessed available literature on global warming of 1.5℃ and on comparisons between global warming of 1.5℃ and 2℃ above pre-industrial levels. It also addressed possible pathways for achieving the ambitious goals of the Paris Agreement. Key findings from this report include the following, directly quoted :
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report