[cmbuck]

Yes, this seems much better than coal/oil, but isn't there a finite amount of heat under Earth's crust? Have we studied what would happen if we cool Earth's internal temperature by extracting heat in this way?

The Magnetoshpere which protects us from radiation is generated by the magma under the crust[1]. Eventually, if we interfere with the magma currents too much, don't we run the risk of damaging our magnetosphere?

[1] https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Physi...

[Retric]

> isn't there a finite amount of heat under Earth's crust?

We can't make meaningful change over the next million years which is vastly past any reasonable projections.

The earth is 6 * 10 ^ 24 kilograms. Changing that much mass by 1 degree would take ~2000 Joules * 6 * 10 ^ 24 kilograms, but we don't get 100% efficiency so let's say it's 10% for a nice low estimate to get 1.2e + 27J.

Worldwide energy use is 5.67 × 10^20J / year. So circa 2 million years of total worldwide energy supply for a 1 degree change. Of course it's not a static value as nuclear reactions and tidal friction are also adding energy, while energy also slowly escapes though the crust.

[cmbuck]

Thank you for this analysis. A 1 degree change over 2 million years strikes me as rather unlikely to meaningfully affect magma currents

[astrodust]

The movie The Core, like so many others, are only plausible if your math is really, really wrong.

[everyone]

I would just guess off the top of my head that, because of the sheer volume of the earths interior and the amount of energy stored there as heat, the energy to run our entire civilisation for 1000's of years would be trival compared to it.

http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/imggeo/ea...

The 4.7 km well is still in the earths crust, not even reached the lithosphere. As far as the earths interior is concerned it might just be like an era of slightly increased vulcanism.

[hwillis]

The heat in the earths core is actively generated as well, by radioactive decay and viscous friction. It's not all just left over heat. In that way it's kind of like asking if windmills will cause the wind to run out. Heat is constantly moving from the interior to the exterior of the earth, and we are really just tapping into that rather than breaching a dam that does not leak.

[sandworm101]

No. The total heat energy down there is astronomical. And earth is heated by the sun. And the heat removed from the rock isnt being flung out into space. Much of it will return through the ground. We are just moving it a few km up from where it is. The earth is thousands of kms thick. We are toying with heat within the pond scum atop an immense ocean of hot rock.

[rb808]

Also excuse my ignorance - but does the heat released warm the Earth's atmosphere? I realize it doesn't create greenhouse gases, but wonder if the newly released heat would make a difference to sea & air temperatures, or just gets radiated away.

[hwillis]

It actually warms the atmosphere infinitesimally less than other methods of generating power (aside from solar, wind or hydro). Normally when you burn something to generate electricity the excess heat is released into the air. The same process, with the same efficiency (in fact, slightly better), still happens in geothermal but it also very very slightly reduces the amount of heat coming up from the earths core elsewhere.

[saalweachter]

The short answer is "it depends what they are using as a cold source". They are probably heating the ocean.