The core puts out 'x' amount of energy that heats the surface area to a certain temp. As the 40,000 miles of oceanic rifts keep expanding, the surface area of the earth increases. That means the average temp gets lower as the same amount of heat now has to heat a larger area. The good news is the cooling starts at the higher elevations first. More land in the 'warm areas' will become available as the ocean level lowers as water turns to ice in 'cooler' areas. The desert belt around the earth will become green, there will be more food available than there is now. Give or take a million years for that change to happen. Until then, enjoy cheap coal