The belief that modern sea levels are unprecedentedly high takes another hit.
In southern South America sea levels were ~6 meters higher than today from 8000-6000 years ago, when CO2 hovered around 265 ppm but it was much warmer with less ice. Sea levels then gradually fell to present levels, the lowest in 8000 years.
“This sea level curve suggests that the LGM lowstand sea level occurred at ~18 ka BP at ~105 m below present sea level. The onset of the marine transgression resulted in rapid sea‐level rise in the Early Holocene, with a highstand of ~6 m above present between 8 and 6 ka BP, followed by a progressive fall to its present position.” – Desiage et al., 2023
Image Source: Desiage et al., 2023
Relative sea level on the coasts of Japan was approximately 2-5 meters higher than today during the Mid-Holocene, then fell to 1 to 1.5 meters higher than today during the Medieval Warm Period before continuing falling to present levels.
“It is known that RSL was higher than today in the mid-Holocene ‘far-field’, remote from the sites of former glaciation and subsequent isostatic rebound (Yokoyama et al., 2012, 2019a; Yokoyama and Purcell, 2021). This far-field elevation is known as the mid-Holocene sea-level highstand (HHS). … The RSL in the Harutachi area at 6000 years ago is estimated to be 0.5–2.5 m asl [above present sea level] (Okuno et al., 2014). … In Utoma, sea regression began around 3.5 kyr cal BP and the altitude of the local HHS is reported to be 2–3 m asl (Nakanishi et al., 2020a). In the Shizunai area, the HHS period continued until ∼4.0 kyr cal BP, when the sea level at that time was 4–5 m asl before falling to 1.0–1.5 m asl at 1.5–1.0 kyr cal BP (Nakanishi et al., 2022a).” – Nakanishi et al., 2023