“[D]uring the last 6 ky, repeated, meter-scale, rapid (<300 y) rises alternated with meter-scale falls…interpreted as global.” – Higgs, 2026

A new study uses excavation evidence (wall ruins, coins, pottery) to suggest sea level rise (SLR) rates reached ~4 m in ~70 yrs (60 mm/year, or 20 times the modern rate of 3 mm/year) from 430 to 500 CE across southern England.

Sea levels reached 3 m higher than today ~1500-2000 years ago, concurrent with the Roman Warm Period. Consequently, the coasts were 1.5 – 3 km farther inland versus today at this time.

Sea level falls were similarly rapid (for example, ~2 m in less than 100 years). Indeed, “dozens of authors found further evidence for Holocene SL [sea level] fluctuations of up to 5 m.”

These SLR rates were absolute or eustatic (due to water loading from melted ice sheets), and the fluctuations were likely global in scale. Similar meters-per-century SLR rates occurred in New Zealand, France, Brazil, and Florida (USA) during this period.

Image Source: Higgs, 2026

A 2024 study indicated that, 8200 years ago, near-global sea levels rose 6.5 meters in a span of just 140 years. This is 470 centimeters per century, 4.7 centimeters per year, during a period when CO2 levels were alleged to be a “safe” and stagnant 260 ppm.

Image Source: Nunn et al., 2024

The net melt of the Greenland ice sheet (GIS) is thought to have been the largest contributor to sea level rise in recent decades. But, to put the GIS change in context, the entire ice sheet melt contribution to sea level rise was just 1.2 total centimeters from 1992-2020 (Simonsen et al., 2021).

Image Source: Simonsen et al., 2021