More directly, I go with undersea volcanism. They still really don’t know the seafloor, not much data on energy leaking out of the mantle.
But what causes the vulcanism to increase?? That takes LOTS of energy. If my hunch is right, and (some/all??)of the magnetic field energy is deposited in magma, then you have the "driver" for the increase in vulcanism.
There is no question that vulcanism HAS increased. THAT there is data for. But why??? I find it hard to believe that photons hitting the earth's surface somehow drive undersea volcanoes.