A detailed review of scientific information has indicated an accelerating rate of sea level rise, and the primary driver behind this phenomenon might not be what one would initially expect. The findings from a new study have been published in the journal Science Advances.
While the melting of glaciers and the diminishing ice sheets are commonly recognized as contributors to a gradual increase in sea levels, the slow and consistent thermal expansion of our oceans often goes overlooked.
However, research suggests that it is precisely this thermal expansion that is the leading cause of rising sea levels globally.
As temperature increases in ocean water, it occupies more space—a process known as thermal expansion—meaning the seawater takes up a larger volume.
According to the researchers in the new study, the expansion of the ocean’s waters is the principal factor behind sea level rise.
The analysis, conducted by an international team of scientists, helps to resolve certain discrepancies observed in prior sea level research, where key factors—including ice melt and ocean warming—did not quite add up to the observed rise in sea levels.
“For many years there has been a frustrating gap between how much the oceans were observed to be rising, and how much we could explain with individual causes,” stated John Abraham from the University of St. Thomas in the USA. “This work shows that with better tools, processes, and more intelligent analysis, this knowledge gap can be filled. We can now explain sea level rise with more confidence.”
This process is referred to as balancing the Global Mean Sea Level (GMSL).
Ensuring that the numbers align is a method to validate the data scientists have collected and to confirm that nothing is being missed in our understanding of what causes sea levels to rise.
This aids in improving the predictions made by climate models that simulate the effects of sea level rise over time and across the globe—so that measures can be taken.
The researchers divided their analysis into three periods: a long-term span from 1960 to 2023 (covered by tide gauge and satellite data), from 1993 to 2023 (the era of satellite imagery), and from 2005 to 2023 (the years scientists utilized oceanographic buoys known as Argo floats).
According to the data, from 1960 onwards, global mean sea level has increased by an average of 2.06 millimeters per year.
However, the rate of increase is accelerating: between 2005 and 2023, it rose by 3.94 millimeters per year—approximately twice the average rate.
The researchers determined that among the contributing factors to this rise, the expansion of warming oceans accounted for 43 percent of this increase.
The melting of mountain glaciers was responsible for 27 percent, the Greenland ice sheet for 15 percent, and the Antarctic ice sheet for 12 percent. The remaining 3 percent is attributed to changes in land water storage.
The researchers believe that advancements in data collection technologies and analytical methods have enabled the accurate balancing of the global mean sea level. For instance, higher-resolution satellite imagery has improved estimates of glacial melt across the planet.
“Although previous studies have closed the GMSL budget, their results diverge due to different selections of datasets,” the researchers wrote. “The current estimates derived from community data allow for reconciliation of differences between multiple estimation methods, reduce random errors caused by the use of a single source, and minimize the influence of dataset choice.”
The researchers warn that these trends are expected to persist for a considerable period. Even with rapid emission reductions, modeling suggests the global ocean will continue to warm for at least another half-century.
The researchers advocate for further work to gather more comprehensive data on land water storage (including reservoirs and irrigation systems) and to identify regional variations in sea level rise.
All of this contributes to a more profound understanding of the potential dangers posed by rising ocean levels, particularly for the most vulnerable populations. It is estimated that millions of lives and livelihoods will be at risk in the coming decades.
The long-term consequences, however, will affect everyone on Earth, irrespective of their proximity to the coast. Rising sea levels will disrupt food chains, trade networks, and population distribution.
A certain degree of damage is now unavoidable, but the extent of this impact remains to be determined.
Limiting emissions to curb global warming will yield benefits, and a complete understanding of the problem’s scope is crucial for minimizing its consequences.
“Accelerating sea level rise poses a significant threat to low-lying coastal areas,” the researchers stated. “Understanding the drivers of sea level rise is paramount for the prediction of future sea level changes and contributes to climate change adaptation and mitigation efforts.”
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