Melting ice sheets in North America were the primary driver of global sea-level rise between 8,000 and 9,000 years ago, according to a new study led by Tulane University and supported by Maynooth University.

The research, published in Nature Geoscience, challenges long-standing assumptions that Antarctica was the dominant contributor during this period.

The study found that retreating North American ice sheets alone caused more than 10 metres of global sea-level rise. This overturns decades of conventional wisdom and suggests that the role of Antarctica was comparatively minor. The findings have implications for understanding the risks of climate change in the present day.

Professor Torbjörn Törnqvist of Tulane University, a co-author of the study, said the amount of freshwater entering the North Atlantic Ocean was much larger than previously believed. This region is critical to the global climate system, influencing ocean currents such as the Gulf Stream. These currents help moderate temperatures in Northwest Europe and affect rainfall patterns in regions like the Amazon.

The study suggests that the climate system may have been more resilient in the past than recent research has indicated. Some studies have warned of a potential weakening or collapse of the Gulf Stream due to modern ice melt, particularly from Greenland. Törnqvist noted that scientists do not yet fully understand what drives this key component of the climate system.

A breakthrough in reconstructing ancient sea levels came when former Tulane postdoctoral researcher Lael Vetter discovered preserved marsh sediments near New Orleans. Radiocarbon dating of these samples extended the sea-level record back more than 10,000 years.

Building on this work, former PhD student Udita Mukherjee combined data from the Mississippi Delta with records from Europe and Southeast Asia. The comparison revealed significant differences in sea-level rise rates that could only be explained by a larger North American ice melt.

Mukherjee, now a postdoctoral fellow at the University of Hong Kong, said the inclusion of high-quality data from Southeast Asia was critical to the study. She emphasised the importance of a global perspective in climate research to improve understanding and support sustainable solutions.

The research was funded by the US National Science Foundation and included contributions from the University of Ottawa, Memorial University in Canada, Maynooth University in Ireland and the University of South Florida.