If you go to a beach this summer, you might end up sunbathing in disputed territory. That’s partly because of climate change and partly because of a legal principle from the Roman Empire. Most beaches have a natural defense against rising seas: The sandy area simply moves landward. But when property owners install sea walls or other barriers to protect beachfront homes and other buildings, the beach has nowhere to go. So it vanishes underwater. Geologists call it coastal squeeze. It’s not a new problem, but it’s been accelerating recently as climate change causes sea levels to rise. And that’s prompting urgent questions about how coastal landscapes should be managed.