> Is this because of geothermal energy leaking upwards

No. The heat energy comes from the sun. Power flux from geothermal is measured in milliwatts per square meter, while the sun can provide more than a kilowatt during the day. So real geothermal heating is negligible at the surface. That's why the temperature a few feet down equals the average annual temperature at the surface.

The only reason people call this "geothermal" is because marketing people realized that this sounds more impressive than "ground source heat pump". It really should not be called "geothermal", because that's something very different. Real geothermal involves extremely deep drilling (not feasible for residential use) or unusual geology.

Geothermal energy: https://en.wikipedia.org/wiki/Geothermal_energy

Geothermal heating > Extraction (GCHE, GHX) || Ground source heat pump (GSHP) https://en.wikipedia.org/wiki/Geothermal_heating

GSHP: Ground source heat pump: https://en.wikipedia.org/wiki/Ground_source_heat_pump

Heat pump: https://en.wikipedia.org/wiki/Heat_pump #Types :

> Air source heat pumps are the most common models, while other types include ground source heat pumps, water source heat pumps and exhaust air heat pumps.

Heat pump > Types:

- SAHP: Solar-assisted heat pump; w/ PV

- acronym for a heat pump with TPV thermophotovoltaic heat to electricity:

- acronym for a heat pump with thermoelectric heat to electricity:

- TAHP: Thermoacoustic heat pump

- ECHP: Electrocaloric heat pump

Electrocaloric effect > Electrocaloric cooling device studies: https://en.wikipedia.org/wiki/Electrocaloric_effect#Electroc...

GCHE, GHX: Ground-coupled heat exchanger: https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger

Acronyms! From https://www.google.com/search?q=Ground-coupled+heat+exchange... :

HGHE: Horizontal Ground Heat Exchanger: a GCHE installed horizontally e.g. in trenches

VGHE: Vertical Ground Heat Exchanger: GCHE installed vertically e.g. in boreholes or piles.

PGHE: Pile Ground Heat Exchanger: A specific type of GCHE that is integrated into the structural foundation piles of a building.

Solar chimney or Thermal chimney: https://en.wikipedia.org/wiki/Solar_chimney

OTEC: Ocean Thermal Energy Conversion: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... and the ecological salinity gradient:

FWIU archimedes spiral turbines power some irrigation pumps in Holland at least. Is there an advantage to double/helical archimedes spirals in heat pumps if/as there is in agricultural irrigation?

Screw turbine: https://en.wikipedia.org/wiki/Screw_turbine

Noiseless double-helical Achimedes spiral wind turbine on a pivot like a pinwheel: Liam F1 average output with 5m/s wind: 1500 kWh/yr (4.11 kWh/day); Weight: ~100 kg / ~220 lbs; Diameter: 1.5 m / 4.92 ft

What about CO2 and heat pumps? Would a CO2 heat pump make sense?

Absorption Heat pump (AHP) https://en.wikipedia.org/wiki/Absorption_heat_pump

Adsorption Heat pump (AHP)

CO2-Sorption Heat Pump: a Adsorption Heat pump (AHP) that uses CO2 as the adsorbate.

NISH: Nano-Ionic Sorption Heat Pump; with e.g. sustainable hydrogels

Is it better to just recover waste heat from other processes; in a different loop?

LDES heat pump

Supercritical CO2 heat pump

Aerogels don't require supercritical drying anymore,

There's also buoyancy. The pyramid builders may have used buoyancy in a column of heated bubbly water to avoid gravity, in constructing the pyramids as a solar thermohydrodynamic system with water pressure.