Source: Journal of Geophysical Research: Solid Earth
Rising seas threaten communities and ecosystems around the world. Efforts to stave off sea level rise—or mitigate the effects—will benefit from accurate predictions of how quickly it could occur.
Now new research by Ding et al. investigates and confirms the existence of a 64-year fluctuation in Earth’s global mean sea level; incorporating this repeating pattern into calculations of sea level rise predictions could improve their accuracy, according to the authors.
The new findings build on earlier analyses of historical tide gauge data that suggested the existence of a fluctuation in global mean sea level that repeats about every 6 decades. Alongside global warming, such a cycle could have contributed to accelerations in sea level rise detected via satellite radar altimetry over the past 30 years.
To confirm the existence of this multidecadal fluctuation, the researchers applied a novel method to analyze data from 44 separate tide gauge sea level records dating from 1933 through 2019. The technique they used is called optimal sequence estimation, which is a data stacking approach designed to detect patterns shared between different geoscience data sets.
The analysis confirmed that alongside fluctuations on other timescales, global mean sea level fluctuates regularly about every 64 years—by an average of about 1 millimeter and up to 18 millimeters in some ocean regions. The researchers validated their findings using additional data from 94 other tide gauges.
The research team also confirmed that the 64-year cycle can have a significant impact on calculations of regional sea level rise, indicating the importance of accounting for it to ensure accurate estimates in the future.
Meanwhile, what causes the fluctuation is unclear. However, the researchers note that it corresponds to certain fluctuations observed in Earth’s magnetic field, as well as to periodic oscillations in the length of a full day on Earth. These other patterns are associated with processes inside Earth’s core, and it is possible that the same core motions underlie the 64-year sea level fluctuation. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2021JB022147, 2021)
—Sarah Stanley, Science Writer
Stanley, S. (2021), Long-term sea level cycle affects predictions of future rise, Eos, 102, https://doi.org/10.1029/2021EO163664. Published on 27 September 2021.
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