[thehappypm]

Just some rough physics..

Q = m c ΔT

m = mass of the crust (roughly 10^22 kg)

C = specific heat of crust (roughly 1000 J/kg·K)

ΔT = 1 K

Q = 10^25 joules would be needed to lower the earths crust by 1 degree K

About 10,000 years worth of today’s human energy consumption

[toomuchtodo]

Following on to this, enough sunlight hits the Earth in 30 minutes to power humanity for a year. So geothermal wouldn’t need to provide all of today’s human energy consumption, just that last bit that renewables, existing nuclear, transmission, storage, and demand response can’t provide for today.

(1GW of solar PV is deployed every 15 hours globally as of this comment)

[conditionnumber]

I wonder how much ΔT you need at the crust to meaningfully change Earth's magnetic field by altering convection patterns in the outer core. I don't know enough physics to attempt an answer.

[lazide]

The outer core is 2,890 KM (~ 1800 miles) below the earths crust, and has the mantle in the way. The crust itself is only 30KM thick. [https://phys.org/news/2017-02-journey-center-earth.html] The crust is basically a thin layer of slag on top of a giant ball of molten everything.

Even at million+ year timescales, I can’t see any way the temperature of the upper crust could matter to the core at all - even if the crust was at absolute zero.

Dirt insulates relatively well, and the amount of thermal mass present is mindboggling.

[thehappypm]

if you lived in the Earth’s core (~6000k) the surface (~300k) would be a rounding error above absolute zero anyway

[conditionnumber]

> would be a rounding error above absolute zero anyway

Kind of joking: unless there are nonlinear effects near 300K? Fig 4 [1] seems to suggest that the thermal diffusivity of the mantle grows very fast as temperature declines past 300K... but the data stop at 200K.

Reason for initial comment: we could probably set up a spherical heat equation to guess how crust cooling would change heat conduction at the outer core. But I have absolutely no idea how to reason about changes in heat conduction affecting the convection dynamics that generate the field. I was silently hoping for one of the domain experts lurking this forum to see it and share wisdom. (But overall it was a silly question, I know).

[1] https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...

[aDyslecticCrow]

Calculating or simulating how earths magnetic field behaves or is generated is quite a complex task. So im doubtful we can usefully estimate it to such precision. It would be interesting though.

[hollerith]

We know that if the convection in the outer core stops, the Earth's magnetic field stops, and removing enough heat from the core will stop the convection.

[aDyslecticCrow]

Yes but calculating the energy draw required for any measurable change in this effect is very different from knowing the rough process it operates on.

We know how weather works quite well, but knowing if it will rain in a week is an entirely different beast.

[hollerith]

I've seen a confident estimate in the form of a calculation. They know what kind of compounds (term?) are in the outer core and they know the minimum temperature those compounds need to be at to be free-flowing enough to sustain the field. And I'm pretty sure we know the current temperature of the outer core.

My memory is that the calculation found that if humanity switched to geothermal for all its energy needs, then in only about 1000 years, the core cools enough for the magnetic field to stop, but I am not sure.

(We should definitely deploy geothermal in the Yellowstone caldera though long enough to cool it down enough so that it will not erupt again.)

[lazide]

That is definitely not true hahaha. The outer core is several thousand km down, and the crust is only 30km thick. And we have the entire mantle below us.

Humanity could max out geothermal for a million years and never make a dent.

[hexpeek]

Whoa, this is a bit scary. As mentioned earlier, it should basically be used in a way where other energy sources are tapped first, and only the shortfall is covered.