Fifty-six million years ago, the Earth experienced an exceptional episode of global warming. In a very short time on a geological scale, within 10 to 20,000 years, the average temperature increased by five to eight degrees, only returning to its original level a few hundred thousand years later. Based on the analysis of sediments from the southern slope of the Pyrenees, researchers from the University of Geneva (UNIGE) measured the impact of this warming on river floods and the surrounding landscapes. The amplitude of floods increased by a factor of eight—and sometimes even by a factor of 14—and vegetated landscapes may have been replaced by arid, pebbly plains. Their disturbing conclusions, to be published in Scientific Reports, show that the consequences of such global warming may have been much greater than predicted by current climate models.