Rising seas are eating Hawaii's beaches, which is bad news for beachfront homeowners and for the tourism-dependent islands, and it is already reshaping property law.

• Most of Hawaii's beaches are wearing away, and Oahu could lose 40% of its beaches within 20 years.
• Higher seas by 2050 mean worse erosion, storm water pushing further inland, flooding on high-tide days every other day, and salt getting into drinking water.
• Hawaii now bans new private seawalls, and sellers must tell buyers if a property is exposed to rising seas or has illegal barriers and fines attached.
• Some North Shore owners refuse to remove sandbags and barriers and are fighting big fines in court, since taking them out could send their homes into the ocean.
• The core fight is whether the state owes owners money for forcing removal, or whether protecting beaches was always a public duty that overrides private claims.

Outlook: The Hawaii Supreme Court will likely have to settle whether beachfront owners get paid when their barriers come down.