The Permian–Triassic Mass Extinction, about 252 million years ago, led to massive loss of marine species and significant declines in terrestrial plants and animals. Intense global warming had been triggered by a period of volcanic activity in Siberia. Super-greenhouse conditions persisted for around five million years afterwards because the demise of tropical forests, and their slow recovery, limited carbon sequestration.
www.leeds.ac.uk/main-index/news/article/5813/new-fossils-reveal-climate-tipping-point-in-most-famous-mass-extinction