Sometime between the Paleocene and Eocene epochs, there was a mysterious, sudden, dramatic rise in global temperature. This moment in time was known as the "Paleocene-Eocene Thermal Maximum", shortened into "PETM". In just 20 to 50 millennia, the temperature rose by five to eight degrees Celsius, and this heatweave persisted for another 200 millennia (that's just the mean estimate.) As a result...well, I'll leave this map to visualize the results for you:
Now in an alternate Earth, the PETM hit at the same time at the same speed, but it persisted for three to four times longer than in our timeline. Would this make the global climate hotter?