Such short-term warming due methane clathrates is certainly possible. A study based on a coupled climate–carbon cycle model (GCM) assessed a 1000-fold (from <1 to 1000 ppmv) methane increase - within a single pulse, from methane hydrates (based on carbon amount estimates for the PETM, with ~2000 GtC), and concluded it would increase atmospheric temperatures by >6 °C within 80 years. https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis#Model...