Overview
- Analyzing 385 studies published from 2009 to 2025, the authors found roughly 90% relied on geoid baselines and another 9% misaligned datasets, with fewer than 1% correctly aligning land and sea measurements.
- Correcting baselines raises present-day coastal water heights by an average of 24–27 centimeters, with discrepancies exceeding 1 meter in parts of Southeast Asia and the Indo‑Pacific and smaller gaps in eastern North America and northern and western Europe.
- Recalculated exposure shows a 1‑meter rise would inundate about 31–37% more land, placing an additional 77–132 million people at risk compared with prior assessments.
- The authors released open coastal sea‑level datasets and tools and urged researchers and planners to rework hazard assessments using properly aligned, locally validated measurements.
- Outside experts acknowledge the technical issue yet caution that some planners already use local data and that adaptation choices will shape how the new baselines translate into on‑the‑ground impacts.