when the earth heats up , it expands.
when the earth cools down, it shrinks.

global cooling would initially bring volcanic action.

Maybe and maybe not. Actually the surface would probably expand with heating.
Here is a link to a discussion somebody started. The main thing is he did some back of the envelope figuring on how much the crust would expand/contract. His calculations said that the equator would expand about 100 meters for 1 degree K. Even if his high end of 480 meters is closer then I don't think that would make a significant increase in volcanic activity. I think that the possibility of increased volcanic activity is based on other considerations. I didn't bother to check those out.

Bill Gill

to me it only seems natural that if the cooling is
occurring from the surface towards the center of the earth , then the magma becomes more pressurized and the lava gets squeezed out by the added pressure of the shrinking crust and upper mantle.

the 4 volcanoes in eastern russia seem to bear that out
but I suppose you have a better more reasonable explaination
as to why they appeared.

a little more information about the area in east Russia.
it makes Yellowstone national park look really tiny.

Paul, you assume lots, and you are also assuming that heating, or cooling changes,
are quickly transmitted through hundreds and thousands of miles of rock,
to effect the sort of changes you are talking about.
===

But, they’ve measured the change in temperature, for the crust of the planet, recently.
Discussed back in 2008 here:

http://www.ldeo.columbia.edu/~jsmerdon/papers/Beltrami_et_al_Journal.pdf
===

While the oceans have warmed the most, over the past 50 years:

The Continental Lithosphere has warmed more than the Atmosphere!

~

"This further supports the conclusion that the observed
warming of Earth during the last fifty years has been truly global
and extends upward into the atmosphere
as well as downward into the Earth’s oceans, cryosphere and continental crust." -Beltrami et al., 2002