Fivefold increase in rate of rising sea levels - study

The rate at which sea levels are rising around Ireland has increased more than fivefold since the beginning of this century, according to a major new scientific study.

Researchers who reconstructed a century of sea-level measurements around the Irish coastline found that the average annual rate of increase has risen from less than 1mm during most of the 20th century to more than 3mm since 2000.

One of the most striking findings is that average sea levels rose by just 1.3cm between 1925 and 1975, a period of 50 years, compared with approximately 9cm in the 31 years between 1993 and 2024.

The research also indicates that sea levels were rising at an annualised rate of approximately 4.3mm by 2024, the fastest rate estimated during the 100-year period examined.

Overall, the scientists calculated that sea levels around Ireland have risen by an average of almost 12cm since 1925.

The study, led by researchers at Maynooth University and published in the scientific journal Ocean Science, provides the most comprehensive assessment yet of how sea levels around Ireland have changed over the past century.

The researchers combined historical and modern tide-gauge measurements from six locations: Belfast, Malin Head, Dublin Port, Cork, Galway and Tarbert in the Shannon Estuary.

They found that the average annual rate of sea-level rise increased from 0.59mm between 1925 and 2000 to 3.13mm between 2000 and 2024.

That represents an increase of more than 400% in the rate of rise between the two periods.

The scientists also calculated that the annualised rate had reached an estimated 4.26mm by 2024, with similarly elevated rates evident around much of the coastline.

Dr Patrick McLoughlin, the lead author and a postdoctoral researcher at Maynooth University's ICARUS Climate Research Centre, said the findings provide a much clearer picture of how sea levels around Ireland have changed.

"The key finding is that the rate we are seeing today is very different from the average rate across most of the 20th century," he said.

"Sea level is rising faster, and understanding that acceleration, including its local variations is crucial for planning for future coastal change."

The scientists found that the acceleration in recent decades is broadly consistent with the pattern of rising global sea levels associated with human-induced climate change.

However, the rate of increase has not been the same around every part of Ireland.

The highest long-term rate identified was at Tarbert in Co Kerry, where relative sea levels increased by an average of 1.43mm annually over the century.

Galway recorded a rate of 1.38mm, compared with 1.28mm at Cork and Malin Head, 1.12mm at Dublin Port and 0.73mm at Belfast.

Some of these differences are explained by the continuing movement of the Earth's crust following the disappearance of the enormous ice sheets that covered parts of Ireland and Britain during the last Ice Age.

Land in parts of the northeast is still rising relative to other areas, while parts of the southwest are experiencing less uplift or some subsidence.

These movements influence how much the sea rises relative to the surrounding land, which is particularly important when assessing the risk of coastal flooding.

The researchers say the findings highlight the need to take account of local conditions when planning coastal protection measures and adapting infrastructure to climate change.

Dr Gerard McCarthy, an oceanographer and Associate Professor at Maynooth University who led the wider sea-level research programme, said the findings represented the culmination of ten years of scientific work.

"For many years, Irish sea level records were too short to conclusively show sea level rise here," he said.

The researchers overcame that problem by recovering and digitising historical observations, including records from Cork, Tarbert and Galway, which had not previously been incorporated into a comprehensive national assessment.

Dr McCarthy described the process as painstaking data archaeology, which enabled scientists to extend their analysis back over a century.

"This landmark publication shows us that climate change-driven sea-level rise is coming home to roost for Ireland," he said.

The findings provide strong evidence of a substantial acceleration in sea-level rise around Ireland since the beginning of this century.

The scientists warn that continued increases will heighten the potential for coastal flooding and inundation, creating growing challenges for communities, infrastructure providers and planning authorities.