Yes, that is thought to have been so but they put out a lot of CO2 as well and particularly when they ignited massive coal seams. CO2 is always one of the gases as is water vapor. Methane is nasty enough. You’ve also got varying amounts of sulfur. Global cooling is a potential if there is a lot of ash and sulfur. You can’t just say that a volcano will cause short term cooling or long term heating. There are a lot of variables. I think with the end Permian the geologic record from the sediments to the fossils will eventually settle the argument -— Oops, I forgot, nothing is ever settled.