If you want to see firsthand the impact of climate change, take a trip to Es Trenc, one of Mallorca’s finest beaches. Here, massive concrete bunkers — once built by Spain’s then-Dictator Francisco Franco — were originally hidden amid the sand dunes. Today, these structures stand out like sore thumbs — rising sea-water levels have swallowed up parts of the beach and radically altered this coastal landscape. In total, scientists have…