How did one volcano confuse scientists, ocean research?

Mt. Pinatubo erupted just before the first sea level temperature-gauging satellite was launched in 1991. Why that matters.

Beawiharta/Reuters/File
Thick ash rises from Mount Sinabung volcano during a 2015 eruption, as seen from Kuta Tengah village in Karo Regency, North Sumatra province, Indonesia.

Could one volcanic eruption skew the data on rising sea levels? Yes, according to new research.

Climate change models have long predicted that sea levels would rise as a result of warming. According to the same models, rising sea levels should also accelerate over time. 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.

Now, researchers might have finally figured out why. According to a study published Wednesday in the journal Scientific Reports, the Mt. Pinatubo volcanic eruption of 1991 actually cooled the planet, temporarily depressing sea levels and throwing off acceleration models.

"When we used climate model runs designed to remove the effect of the Pinatubo eruption, we saw the rate of sea level rise accelerating in our simulations," said NCAR scientist John Fasullo, who led the study, in a statement.

As water warms, it occupies increasingly more volume – an effect of thermodynamics. Meanwhile, melting ice sheets displace liquid water into the ocean, raising sea levels. But the actual rate of rise can fluctuate, so it’s imperative that scientists have an accurate model of acceleration.

Mt. Pinatubo, located on the Philippine island of Luzon, spewed 10 billion tons of magma when it erupted on June 15, 1991. Months later, NASA and French space agency CNES launched the first satellite altimeter, TOPEX/Poseidon, to monitor sea level from orbit. Many studies on sea level trends are based on data from the satellite.

But that original data was skewed, Dr. Fasullo and his colleagues say. The Pinatubo eruption ejected a huge mass of aerosols that blocked sunlight and temporarily cooled the oceans. As a result, the sea level dropped by about six millimeters.

Soon after, sea levels returned to normal. This rapid rise created an artificial impression of acceleration, researchers say, which masked subsequent accelerations.

"Now that the impacts of Pinatubo have faded, this acceleration should become evident in the satellite measurements in the coming decade,” Fasullo said, “barring another major volcanic eruption."

It’s still unclear exactly how fast acceleration is happening or where sea levels will be at the end of the century. But in the meantime, Fasullo and colleagues have answered a critical, lingering question of climate change.

“Accelerated sea level rise is real, and it's ongoing,” Fasullo told The Washington Post, “and it’s not something we should doubt based on the altimeter record.”

You've read  of  free articles. Subscribe to continue.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.