Comment by epohs

Tough to tell exactly what you’re referencing, but you might be thinking about the Paleocene–Eocene thermal maximum, which was a natural increase in carbon in the atmosphere that led to higher temperatures. So, in some ways very similar to what we’re seeing now, but if my understanding is correct, even the PETM which was “dramatic” on a geological timescale took thousands of years to ramp up, and played out over 200,000 years. What we’re seeing now is happening much quicker, and is highly correlated with human influence.