Well, I may show my "crackpot" side here, but I think that there is a physical mechanism that can explain both global warming AND earthquakes, but it doesn't depend on CO2.
Specifically, the sun's magnetic field encompasses the earth. The earth is moving within that field. Physics says that anytime a conductor (and the earth's molten interior is most definitely "a conductor) moves in a magnetic field that an electric current is produced. The sun's magnetic field has DOUBLED in strength over the time we have measurements for. So, where does that energy which MUST be generated in the interior of the earth go??
I personally think that it is this non-photonic mechanism that explains most global warming, increased vulcanism, and increased earthquake activity, but thus far I have found ZERO scientific (or even non-scientific) discussion even of the concept.
Interesting theory. My understanding is that geothermal heat flux to the surface is fairly minimal compared to the incoming solar to the surface. Wikipedia says it is 10,000:1 which even if they are exaggerating by an order of magnitude, there’s still 1000x more heat from the sun than from the interior of the earth.