I'm sceptical how global warming could affect tectonic activity, especially volcanism. However, I think the guy has a point regarding the change of sea level at the end of ice age and that the situation might be somewhat comparable. After all, the end of the ice brought about a vast increase of the shelf areas being submerged that were previously dry land (like the Doggerland).
from my point of view, global warming means that also Earth's core is warming up... it can happen in periods when sun's activity is much stronger (periodic process)...and with increased temperature fluids expand, so global warming would easily cause earthquakes and increased volcanic activity....
very small increase in temperature of Earth's core means that its volume and surface needs to be significantly larger (significantly from our point of view as we live on a thin layer of dried cool surface of a melting hot ball).... so what happens is that either expanding fluid pushes tectonic plates to increasingly move or when that is not enough it explodes through a holes on the surface (those holes we know as volcanos)
but global warming also can cause global cooling.... extremely increased volcanic activity can cause volcanic winters due to lot of ash preventing sun rays to reach the earth...so sun stops heating the earth and its surface and core cool down... explosions of megavolcanos could be a significant part of mechanism that triggered ice ages in the past....and those explosions are caused by earth's core expanding due to long period of extreme sun activity...
it is earth's way to achieve stability by having periods of global warming and global cooling exchanging in sequence as a reaction to regular changes in strength of sun activity (probably not simply periodic - several different frequencies involved)......though amplitudes of extreme cooling and warming are probably becoming less extreme with time because earth's core is also cooling down exponentially...
during global cooling life on earth is just surviving in few refuge areas...
mega earthquakes would be a reaction to a moderate increase of sun activity, mega volcanos would be reaction to extreme sun activity when small movements of tectonic plates are not enough to compensate need of hot fluid of earth's core to expand...
sun has increased activity in last decades, but I do not believe it is anywhere near to trigger a megavolcano that can cause global cooling....but is possibly enough to continue with trend of some mega earthquakes in next years..
this is all elementary physics... i am surprised that there seems to be no exact model with identified parameters... guess it is because geology scientists are not really engineers.. instead all those non engineer scientists give us stories of CO2 effect theory that should make us feel guilty...but they do not provide exact models... they base theory on observing correlation in shape of curves representing temperature and CO2 and disregard that increase of CO2 in past comes from increased volcanic explosions that are a consequence of sun's extreme activity warming up Earth's core, and not actual cause of the temperature increase... ozone layer is another story as it does keep Earth from warming up and is now damaged by our activity, but not due to CO2 increase, but because of massive use of other gasses (e.
g ones based on chlorine (Cl), and bromine (Br). ) that damage it