Global surface heat flow

Because of the variability of 1/ rock's conductivity and radiogenic heat production, 2/ the thickness of continental and oceanic crusts, 3/ sedimentation or erosion rates at the Earth's surface, 4/ mantle heat flow (mantle upwelling or downweling in the asthenospheric mantle), one can expect large variation of the lithospheric geotherm. The surface heat flow is a proxy for geotherm. Regions with "warmer" geotherms are characterized by higher surface heat flow, whereas regions with "colder" geotherms are characterized by lower surface heat flow. Over the past few decades, measurements of surface heat flow have revealed that the heat flow at the Earth's surface is largely inhomogeneous with oceanic area releasing 2 to 3 times more heat than continental areas. This is because oceanic lithospheres are thinner than continental lithospheres with therefore larger conductive heat transfer in oceanic areas.