Constraints on global mean sea level during Pliocene warmth

Area of Science:

• Paleoclimatology
• Sea Level Science
• Ice Sheet Dynamics

Background:

• Reconstructing past sea levels is crucial for understanding ice sheet responses to prolonged warming.
• Existing estimates of Pliocene global mean sea level (GMSL) have considerable uncertainty, limiting assessments of ice sheet stability.
• The Pliocene epoch, particularly warmer periods like the mid-Piacenzian Warm Period and Pliocene Climatic Optimum, serves as a valuable analog for future climate scenarios.

Observation:

• New GMSL data were derived from phreatic overgrowths on speleothems in Mallorca, Spain, spanning 4.39 to 3.27 million years ago.
• This speleothem record offers a unique, sea-level-linked archive with reliable U-Pb dating and a long timespan.
• The data allowed for quantification of uncertainties related to potential tectonic uplift.

Findings:

• During the mid-Piacenzian Warm Period (2-3°C warmer than pre-industrial), GMSL was approximately 16.2 m higher due to ice-volume changes, reaching 17.4 m with thermal expansion.
• During the Pliocene Climatic Optimum (4°C warmer than pre-industrial), GMSL was 23.5 m above present levels, with an additional 1.6 m from thermal expansion.
• Six distinct GMSL data points were established for the Pliocene, providing a more precise sea-level curve.

Implications:

• The findings demonstrate the high sensitivity of Earth's ice sheets to even moderate global warming.
• This detailed Pliocene GMSL reconstruction provides critical calibration targets for improving future ice sheet models.
• Understanding past sea level dynamics is essential for predicting future coastal impacts and informing climate policy.