Endless geothermal heat from the core is clearly the answer:
my favorite comment: "Removing heat from the mantle through millions of these geothermal bore holes, thus cooling the mantle. What could possibly go wrong?"
oh ffs.
for starters, killing our magnetic field, removing the protection we enjoy from solar radiation that also keeps our atmosphere from blowing away in the solar wind. There wouldn't be anybody left to enjoy the irony of actually destroying our planet while trying not to make it too warm.