San Francisco's Treasure Island Is Sinking, but Rising Seas Will Soon Matter More

Treasure Island, a century-old artificial island in San Francisco Bay, is sinking at 5 to 11 millimeters a year, and its northwest corner is sliding sideways at up to 6 millimeters a year. Guoqiang Shi of The Hong Kong Polytechnic University and colleagues report the measurements in Communications Earth & Environment, published Nov. 12, 2026.

The authors project that sea-level rise will overtake the sinking ground as the main contributor to the island's flood exposure by 2030, and that under high greenhouse-gas emissions the island faces significant risk of flooding inland by 2050. Both dates come from models, not from measurements.

The study combines historical records, decades of satellite radar measurements of ground movement, three-dimensional modeling of how the ground deforms, and projections made with deep learning. It traces the sinking and the sideways movement to a foundation that is compressible and uneven.

The authors describe the island as a test case for aging land built out into the sea, point to acute problems for the redevelopment already planned there, and offer their approach as transferable to other reclaimed coasts with similar ground and climate.

The paper is open access. Communications Earth & Environment has posted it as an accelerated preview, a peer-reviewed version that carries a permanent DOI and will be replaced by a final version of record. The National Natural Science Foundation of China, the Research Grants Council of Hong Kong and the Otto Poon Research Institute for Climate-Resilient Infrastructure funded the work.