Letter: Heating Earth's crust

From John King

Mike Follows’s letter (5 February, p 28) shows a lack of understanding of the subject of crustal expansion first raised by Peter Mockeridge and Nathalie Bugeaud (15 January, p 28). His calculation that global warming will cause heat to penetrate downwards by only 10 millimetres is not worth the envelope it was written on. Thermal conductivity does not work like that, and anyway the Earth’s crust is being heated from below. That a NASA spokesman should reject Mockeridge and Bugeaud’s entirely reasonable and well-founded thesis only goes to confirm the impression that new ideas do not figure in the agency’s current ethos.

Speaking broadly, the crust is in a steady thermal condition, conveying heat upwards from the mantle to the atmosphere, in places via the oceans. But if the temperature of the atmosphere changes, so will the temperature of the rocks at the surface and the thermal gradient throughout the Earth will readjust, over a timescale of centuries.

Mockeridge and Bugeaud’s estimate that this mechanism is capable of producing 20 metres of overthrust at tectonic plate margins for a rise of only 1 kelvin has a horrible current relevance given the Asian tsunami, but this effect is probably not going to cause earthquakes where otherwise none would have occurred. Rather, we should expect intervals between earthquakes to be shorter during periods of global warming, and for some time after temperatures stabilise at the surface.

Of course global cooling would generate a similar influence.

Wymondham, Norfolk, UK