It’s no secret that sea levels are rising due to global warming.
What might come as a shock, however, is the discovery that the rate of this rise is accelerating, a finding long hidden by an extraordinary natural event.
The culprit? A volcanic eruption so massive it distorted decades of climate science.
On June 15, 1991, the Mount Pinatubo eruption in the Philippines became the second-largest volcanic event of the 20th century.
This cataclysm spewed 5 cubic kilometers of debris into the air, with an ash cloud towering 35 kilometers (22 miles) above Earth’s surface.
The eruption unleashed 18 million tonnes of sulfur dioxide into the atmosphere, creating a reflective veil that cooled the planet by about 0.5°C (1°F) from 1991 to 1993.
Remarkably, this coincided with the launch of TOPEX/Poseidon, the first satellite altimeter designed to measure sea level changes.
The timing was devastating for climate science. Instead of accurately documenting the impact of warming on sea levels, the data captured a distorted reality—a short-term cooling period caused by the volcanic aftermath.
The result? Decades of confusion about why sea levels seemed to rise at a steady, linear pace when they should have been accelerating.
Volcanoes, Satellites, and a Climate Science Conundrum
When TOPEX/Poseidon launched in 1992, scientists expected its precise radar altimeter to confirm what they already suspected: that rising temperatures were driving melting ice caps and thermal expansion of seawater, causing sea levels to rise at an accelerating rate.
Instead, the satellite recorded a consistent rise of 3.5 millimeters per year (1.4 inches per decade).
For the first decade of its operation, the data showed something even more perplexing—a slight decline in sea levels.
This anomaly left scientists scratching their heads. If the Earth’s temperature was breaking records year after year, why wasn’t sea level rise keeping pace?
“We’ve been looking at the altimeter records and saying, ‘Why aren’t we seeing an acceleration in the satellite record?
We should be,'” explained John Fasullo, a climate scientist at the US National Center for Atmospheric Research.
The answer, it turns out, was buried in the sulfur-rich plume of Mount Pinatubo.
The eruption caused a massive ocean cooling event as the volcanic gases reflected sunlight back into space, temporarily lowering global temperatures.
This, in turn, masked the underlying effects of climate change on sea levels.
A Hidden Acceleration
To untangle this mystery, Fasullo and his team developed 40 advanced climate models, treating the Mount Pinatubo eruption as an anomaly.
Their findings were revelatory. The volcanic cooling caused a temporary 5-7 millimeter drop in sea levels, followed by a rebound effect once the cooling subsided.
This rebound created the illusion of steady sea level rise when, in reality, the data was skewed.
“The results were completely distorted,” said Fasullo. The apparent stability in sea level rise obscured the fact that it was actually accelerating, consistent with the intensifying effects of global warming.
With these corrections, scientists now have the first concrete evidence of an accelerating rise in sea levels.
However, because this recalibration essentially resets our understanding of historical data, it’s too early to quantify the exact rate of acceleration.
Fasullo estimates that within 5 to 10 years, we’ll have a clearer picture.
Why This Matters Now More Than Ever
For decades, the narrative around sea levels suggested slow, manageable change. This new research challenges that assumption.
An accelerating rise in sea levels has dire implications for coastal communities, which house nearly 40% of the global population.
If the current pace continues to quicken, cities like Miami, New York, Jakarta, and Tokyo could face more frequent flooding, infrastructure damage, and the displacement of millions.
And it’s not just the human cost—ecosystems like mangroves and coral reefs, critical to coastal resilience, could be irreversibly damaged.
Moreover, the deceptive stability of past sea level data may have lulled policymakers into a false sense of security.
“Our initial impression of sea level rise was not only influenced by climate change and the rate of change but also the recovery from the eruption itself,” Fasullo explained.
What Comes Next
While Mount Pinatubo’s eruption obscured critical climate data, it also underscores the complexity of Earth’s interconnected systems.
Volcanic cooling, though temporary, offered a rare natural experiment—an unintentional case study in how the planet reacts to sudden changes in atmospheric composition.
Looking ahead, scientists are eager to refine their models further.
By integrating more comprehensive data and extending the satellite record, they hope to better predict the pace of future sea level rise.
In the meantime, the evidence is clear: sea levels are not just rising—they’re rising faster than we realized, and the consequences will ripple across economies, ecosystems, and societies.
As Fasullo points out, “Once we get a few more years into the altimeter record, we should see a clear acceleration.”
A Call to Action
The realization that sea level rise is accelerating comes with an urgent call to act.
Governments must invest in climate adaptation strategies, from building resilient infrastructure to restoring natural barriers like wetlands.
Meanwhile, individuals can play a role by advocating for policies that curb emissions and mitigate the root causes of global warming.
The story of Mount Pinatubo reminds us of the planet’s unpredictability and our responsibility to understand and adapt to it.
As science catches up with nature’s complexities, one thing is certain: the time to act is now.
For those living along coastlines, the accelerating rise of the oceans is no longer a distant concern—it’s a pressing reality.
