My point is not that the event won't happen as before, but that mankind may have absolutely nothing to do with it.
I've read some other articles about the PETM. The cause of the methane release appears to have been a fairly rapid decrease in sea level (cause unknown, as far as I can tell), leading to destablization of the sea floor methane deposits, which released into the atmosphere, and apparently were then converted to CO2, prolonging the initial warming caused by the methane. This process wasn't an all-at-once event, either.
Under current conditions, thought methane was increasing a bit in the atmosphere, the main gas on the rise is CO2. IF (big if) CO2 can induce the same temperature effect as the methane --> CO2 did in the PETM, it's possible that there could be ocean circulation changes, as other research has indicated. The main question is how much temperature change the increasing CO2 in the atmosphere will cause.