Paleoclimatology observations are useful to assess multiple hazards of environmental change while excluding direct anthropogenic impacts . Ancient intervals of rapid climate warming that occurred between 300 and 50 million years ago  were triggered by the release of greenhouse gases . The sources of greenhouse gases varied but include volcanic degassing from continental flood basalts and methane hydrates stored in marine sediments and soils . Six extreme ancient hyperthermal events are known from the last 300 Ma, when tropical SSTs reached 1.5°C-10℃ warmer than pre-industrial conditions, and with substantial impacts on ancient life . Warming and deoxygenation in the oceans were closely associated in hyperthermal events , with anoxia reaching the photic zone and abyssal depths , whereas ocean acidification has not been demonstrated consistently  .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report