Geomagnetic storms are temporary disturbances of Earth's magnetosphere. They are caused by solar wind shock waves or clouds of magnetic field interacting with the Earth's magnetic field. A severe geomagnetic storm could potentially shut down power grids on a continental scale for months.
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Roodman, David (2015d) Coming down to earth: what if a big geomagnetic storm does hit?, Open Philanthropy, August 21.
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