Mid-Holocene South China Sea Level 2-3 Meters Higher Than Today Due To 1-2°C Warmer Temps

The mechanisms driving the meters-higher sea levels a few thousand years ago do not support claims that CO2 is a driver.

A comprehensive analysis (Zhang et al., 2025^[1]) of the South China Sea region indicates warmer sea water was fundamentally responsible for sea levels that were, on average, 2-3 meters higher (and in some regions as much as 5-7 meters higher) than today from approximately 7000 to 4000 years ago.

“Understanding Holocene high sea levels in the South China Sea (SCS) is critical for understanding climate change and assessing future sea-level rise risks. We provide a comprehensive review of the Holocene highstand in the SCS, focusing on its age, height, and mechanisms. Records reveal a wide range for this highstand: ages span 3480–7500 cal yr BP, while elevations range from −7.40 to 7.53 m relative to the present. Positive elevations dominate (80.5% of records), with the most frequent range being 2–3 m.”

“…the Holocene high sea level in this region occurred between 7200 and 5000 yr BP…at least 2.9-3.8 m higher than today.”

Image Source: Zhang et al., 2025^[2]

It is assumed the meters-higher Holocene sea level highstand in the South China Sea (SCS) region are a function of global-scale mechanistic processes (glacial meltwater input, thermal expansion).

“Regionally averaged formation times suggest a broadly synchronous mid-Holocene high-sea-level event across the SCS, potentially reflecting a global background. The observed variability is attributed to the interplay of multiple factors: global processes like glacial meltwater input and seawater thermal expansion, particularly during the Holocene warm period, and regional neotectonic movements (uplift/subsidence), which are the primary cause of spatial differences in reconstructed elevations.”

Variance in temperature is the “fundamental controller of sea level” in the SCS.

Because CO2 concentrations were a “safe” and relatively static 265 ppm from approximately 7000 to 4000 years ago and yet sea surface temperatures were 1-2°C warmer than today and sea levels 2-3 meters higher, it can be concluded CO2 is not an influential mechanism affecting warming, thermal expansion, glacial meltwater input, or sea level variability.

“The mean annual temperature in the Holocene Climatic Optimum in South China and adjacent subtropical East Asia was about 1–2 °C higher than that of the present day. Rising temperatures cause glaciers to melt, which in turn causes sea levels to rise. This relationship implies that temperature is a fundamental controller of sea level in the SCS.”