A new tropical Atlantic subsurface temperature reconstruction indicates it was 7°C warmer than today during the Younger Dryas/Bølling-Allerød (~15,000-11,500 years ago), when CO2 concentrations hovered around 210-220 ppm.
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003376
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003376