The British Prime Minister Tony Blair declared recently that there was no bigger long-term question facing the global community than the threat of a climate change due to man-made greenhouse gases. Unfortunately, the focus is misplaced. It is not the atmosphere which determines the fate of the climate. It is the ocean which does it. Naval warfare during the two World Wars determined two major climate changes: a sustained warming which started at the end of World War I and lasted 20 years, and the next climatic shift which started during the winter 1939/40 and caused a four-decades global cooling. The extensive fighting at sea was a real threat for the normal course of the climate. How could the course of international conflicts have been managed if the world's leading statesmen of the 20th century had been concerned with the climatic changes due to the impact that a war at sea could have had on the ocean and on the climate? Would Adolf Hitler have reconsidered his war aims in the summer of 1939 if the United States had warned him of their immediate implication in the looming war in case his decision would bring 1000 naval ships out on sea, thus generating a substantial climatic shift? The naval war thesis is an intriguing contribution to the 'global warming issue' and has the potential of revolutionising the current climate change debate.