Effective way to cause global extinction.
effective way to prevent the global cooling issue
this would make the species be a intergalactic species possibly as fragments of dead life will go to other galaxies maybe, maybe as a meteor due to accumulated stone ontop
As a result, the engines would be left to run unsupervised until the planet collided with a cosmic giant; most likely a star but possibly a neutron star or a black hole. So this project would cause the extinction of all life on that planet.
If the artificial volcanoes were built 4-5 times the height of Everest and with more power than any natural volcanoes, than propulsion could be acheived. Of course, as demonstrated in the save, this would burn all the oxygen on a planet and heat up the atmosphere to dangerous levels, killing of life. *Continued on the next comment*
it won't even work. Since volcanoes do not eject material from the planet into space at high speed, no velocity is added or subtracted. Therefore nothing happens to the planet's orbit.