claim: The most notorious was 252 million years ago; it began when carbon warmed the planet by five degrees, accelerated when that warming triggered the release of methane in the Arctic, and ended with 97 percent of all life on Earth dead.”
evidence: The IPCC's Fifth Report, released in 2014, states that relative to the average from year 1850 to 1900, global surface temperature change by the end of the 21st century is likely to exceed 1.5 °C and may well exceed 2 °C for all RCP scenarios except RCP2.6.