Now, after more than twenty years of head-scratching, we finally have an explanation: the Mt. Pinatubo volcanic eruption of 1991. But while concrete increases in sea level have been recorded, the rate has remained at a consistent 3 millimeters per year for over two decades. However, the anticipated acceleration expected to result of climate change is likely obscured in the satellite record, due to the coincidence of the Pinatubo eruption, which cooled the Earth temporarily and lowered sea levels.
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The study lends support to climate model projections that show the rate of sea level rise escalating over time as the climate warms.
The new study was led by the National Center for Atmospheric Research (NCAR) and is published in the journal Scientific Reports.
‘Now that the impacts of Pinatubo have faded, this acceleration should become evident in the satellite measurements in the coming decade, barring another major volcanic eruption’.
Study co-author Steve Nerem of the University of Colorado Boulder, added: “The study shows that large volcanic eruptions can significantly impact the satellite record of global average sea level change”.
Amazingly, this all happened at the same time as when NASA and French space agency CNES chose to launch the world’s first satellite altimeter, called TOPEX/Poseidon, which would allow scientists to start monitoring sea level changes from orbit. Decision-makers have debated whether communities should make plans based on the steady rate of sea level rise as measured by satellites in recent decades, or based on the accelerated rate expected in the future as predicted by climate scientists.
However, as the aerosols emitted by the volcano slowly dissipated, sea levels began to slowly rise to pre-eruption levels, delaying the recorded sea-level rise to the late 1990s. Analysis of the satellite record has not borne that out, however. Indeed, the eruption had a cooling effect, because of the sunlight-blocking volcanic aerosols that were emitted – so the real impact of rising temperatures on ocean levels may have so far been concealed.
This rebound made it look like sea levels experienced a sharp increase, followed by a decline, and then ultimately, it appeared to even itself out, but in reality, the results were completely distorted.
The study, Kopp explained by email, found that the Pinatubo eruption would have caused seas to fall “just before the start of the altimetry record, the recovery from which was spread out of the remainder of the 1990s and therefore masked some of the acceleration that would otherwise have been seen in the tide-gauge record between the 1990s and the 2000s”.
In 1991, Mount Pinatubo in the Philippines erupted in what was the second biggest volcanic eruption this century.
In fact, for the first decade of operation, the radar altimeter actually showed a decrease in sea level – not exactly what you’d expect when the planet continues to break temperature records every year, and the melting of our icebergs has accelerated.
Prior to the launch of the worldwide TOPEX/Poseidon satellite mission in late 1992, sea level was mainly measured using tide gauges.
“It sounds like a small number”, he said of the 3.5-millimeter annual increase in sea levels, but “when you have exponential growth, that can quickly become a big number”. In the early days of monitoring sea level from space, Earth’s oceans were rebounding from the temporary effect of the volcano, causing the rate of sea level rise to be artificially high.
The study was funded by NASA, the U.S. Department of Energy, and the National Science Foundation, which is NCAR’s sponsor.
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“The satellite record is unable to account for everything that happened before the first satellite was launched, ” Fasullo said. In fiscal year (FY) 2016, its budget is $7.5 billion. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards.
