Ice Age sea levels and changing coastlines

How much lower was the sea?

The IPCC AR6 assessment gives an LGM global mean sea level roughly 125–134 m below present. This is an assessed range, not a guarantee that every coast stood exactly 130 m lower. Sea-level evidence and reconstructions carry uncertainty.

References: IPCC (2021) — AR6 Working Group I, Chapter 9, Table 9.6

What the timeline actually displays

This atlas uses the sea-level stack of Spratt and Lisiecki, distributed by NOAA. We subtract the stack’s 0 ka value of +8.49 m from every sample, so the map’s present-day reference is zero. We linearly interpolate the supplied 1,000-year samples.

The paper reports average uncertainty of roughly 9–12 m at one standard deviation across its stack. That is not a point-specific uncertainty interval for this map. A slider with 100-year steps does not create 100-year evidence.

References: Spratt & Lisiecki (2016) — A Late Pleistocene sea level stackNOAA Paleoclimatology — Spratt and Lisiecki sea-level dataset

Why local coastlines differ

Relative sea level describes the sea surface compared with the land at a location. Ice loading and unloading deform the solid Earth, and changes in ice mass also affect gravity and ocean water distribution. Local sea-level histories therefore differ from the global mean.

The atlas compares modern ETOPO1 elevation against a single global level. It omits regional sea-level change, glacial isostatic adjustment, sediment changes and checks for connection to the open ocean. Treat the resulting coastlines as broad geographic context, not surveyed ancient shorelines.

References: IPCC (2021) — AR6 Working Group I, Chapter 9, Table 9.6NOAA — ETOPO1 Global Relief Model

Read the colours carefully

The exposed-land layer highlights modern submerged terrain that lies above the selected sea-level threshold. It does not identify settlements, vegetation, navigable rivers or a proven migration route. Use the regional guides for the evidence behind individual landscapes.