evidence: The Intergovernmental Panel on Climate Change is the international United Nations group tasked with summarizing climate change research every few years. Their 2013 report projected that sea level will rise by 2 to 3 feet by 2100 if we do not slow our carbon dioxide emissions by using less energy or using renewable energy. That is enough to threaten coastal cities and flood island nations. Even if we reduce our emissions, the report predicts that by 2100 sea level will rise by 1-2 feet, which is enough to cause much coastal flooding and erosion. Some scientists consider these estimates to be conservative, and expect greater sea level rise. The U.S. National Climate Assessment, for example, estimates that sea level will rise between 2 and 6 feet by 2100.