Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere—probably linked to changes in deep ocean circulation—occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling–Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known.