Rainfall-magnetic field link during the Holocene

One of the fuelling factors in the debate about short-term climate change during the Holocene is the suggestion that variations in cosmic-ray bombardment might affect climate through these extra-solar particles’ possibly nucleating low-altitude clouds. It is a complicated idea, because changes in the Sun’s activity – the solar wind – modulate the cosmic ray flux, and short-term changes in solar irradiance at the Earth’s surface have also been suggested as a climate driver. To further obscure matters, any changes in the geomagnetic field would also affect cosmic-ray flux, yet geomagnetism is in turn a measurable proxy for cosmic ray intensities on Earth (Knudsen, M.F. & Riisager, P. 2009. Is there a link between Earth’s magnetic field and low latitude precipitation? Geology, v. 37, p. 71-74). The two Danish scientists have compiled the Holocene record of the geomagnetic dipole moment: effectively a measure of the strength of the magnetic field. In the paper they compare that record with δ18O changes in stalactites from China and the Oman, which are a proxy for changing low-latitude precipitation – in part the signal of the Indian Ocean monsoons. A correlation did emerge from the study, supporting the cosmic ray-climate theory. This further complicates the Earth’s climate system and therefore the models used by climatologists.

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