Unstoppable Global Warming: Every 1,500 Years is a book about climate change, written by Siegfried Fred Singer and Dennis T. Avery, which asserts that natural changes, and not CO2 emissions, are the cause of Global Warming. Published by Rowman & Littlefield in 2006, the book sold well and was reprinted in an updated edition in 2007. The title refers to the hypothesis of 1,500-year climate cycles in the Holocene first postulated by Gerard C. Bond, mainly based on petrologic tracers of drift ice in the North Atlantic.