NicoleC, here is a link to a BBC documentary on the Permian Extinction: Click here.

The alarming thing about this extinction was its short timescale. The temperature went up by 5 degrees Centigrade / Kelvin over a few hundred thousand years; then in probably twenty to fifty thousand years, almost all life in the oceans died, and the temperature went up another 5 degrees.

The cause of the initial 5 degree rise was probably the eruption of the Siberian Traps; about twenty times the area and forty to fifty times the volume of the Columbia River basalts. There isn't likely to be vulcanicity on the same scale for the foreseeable geological future, but releasing all the CO2 buried and fixed in fossil fuels seems like a good way to try and repeat the same conditions, experimentally.