The theory of 1,500-year climate cycles in the Holocene was postulated by Gerard C. Bond of the Lamont-Doherty Earth Observatory at Columbia University, mainly based on petrologic tracers of drift ice in the North Atlantic. Later proponents of this view include S. Fred Singer of the University of Virginia and Dennis Avery of the Hudson Institute, an American think-tank. They suggest that the current global warming is a Bond or Dansgaard-Oeschger event, and is therefore natural and unstoppable. See also: Error: Template must be given at least one article name