Volcanic eruption masked acceleration in sea level rise

Volcanic eruption masked acceleration in sea level rise
Mount Pinatubo's 1991 eruption and its effects masked sea level rise. Credit: USGS

The cataclysmic 1991 eruption of Mount Pinatubo in the Philippines masked the full impact of greenhouse gases on accelerating sea level rise, according to a new study.

"These scientists have disentangled the major role played by the of Mount Pinatubo on trends in global mean ," said Anjuli Bamzai, program director in the National Science Foundation's Division of Atmospheric and Geospace Sciences, which funded the research. "This research is vital as society prepares for the potential effects of climate change."

Satellite observations of the ocean surface, which began in 1993, indicated the rate of sea level rise was holding fairly steady at about 3 millimeters per year. As the pace of warming oceans and melting glaciers and ice sheets accelerated, scientists expected to see a corresponding increase in the rate of sea level rise. Analysis of the satellite record has not borne that out, however.

Researchers have now determined that the expected increase in sea level rise due to climate change was likely hidden because of a happenstance of timing: Pinatubo erupted in 1991, two years before the first satellite observations of the ocean began. The eruption, which temporarily cooled the planet, caused sea levels to drop and effectively distorted calculations of sea level rise in subsequent decades.

The study lends support to climate model projections that show the rate of sea level rise escalating over time as the climate warms. The findings were published today in the open-access journal Scientific Reports, published by Nature Publishing Group.

"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 National Center for Atmospheric Research (NCAR) scientist John Fasullo, who led the study. "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 . So we must be careful to consider these effects when we look for the effects of climate change in the satellite-based sea level record."

The findings have implications for the extent of sea level rise this century and may be useful to coastal communities planning for the future. 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.

Volcanic eruption masked acceleration in sea level rise
In this simulation, the rise in sea level puts the coast of Louisiana underwater. Credit: NASA

Reconstructing a pre-Pinatubo world

Fasullo and Nerem, along with Benjamin Hamlington of Old Dominion University, wanted to pin down how quickly sea levels were rising in the decades before the satellite record began.

Prior to the launch of the international TOPEX/Poseidon satellite mission in late 1992, sea level was mainly measured using tide gauges. For the researchers, variations in measurement technique and location meant that the pre-satellite record was best used to get a ballpark estimate of global mean sea level.

To complement the historic record, the research team ran the NCAR-based Community Earth System model 40 times with slightly different—but historically plausible—starting conditions. The resulting simulations characterize the range of natural variability in the factors that affect sea levels. The model was run on the Yellowstone system at the NCAR-Wyoming Supercomputing Center.

A separate set of model runs that omitted volcanic aerosols—particles spewed into the atmosphere by an eruption—was also assessed. By comparing the two sets of runs, the scientists were able to pick out a signal (in this case, the effect of Mount Pinatubo's eruption) from the noise (natural variations in ocean temperature and other factors that affect sea level).

"You can't do it with one or two model runs—or even three or four," Fasullo said. "There's just too much accompanying climate noise to understand precisely what the effect of Pinatubo was. We could not have done it without large numbers of runs."

Using models to understand observations

Analyzing the simulations, the research team found that Pinatubo's eruption caused the oceans to cool and sea levels to drop by about 6 millimeters immediately before TOPEX/Poseidon began making observations.

Volcanic eruption masked acceleration in sea level rise
Sea level rise puts wetlands along US coastlines and around the world at risk. Credit: NOAA

As the sunlight-blocking aerosols from Mount Pinatubo dissipated in the simulations, sea levels began to slowly rebound to pre-eruption levels. This rebound swamped the acceleration caused by the warming climate and made the rate of sea level rise higher in the mid- and late 1990s than it otherwise would have been.

This higher-than-normal rate of sea level rise in the early part of the satellite record made it appear as though the rate of sea level rise was not accelerating over time. In fact, according to the study, if the Pinatubo eruption had not occurred—leaving sea level at a higher starting point in the early 1990s—the satellite record would have shown a clear acceleration.

"The satellite record is unable to account for everything that happened before the first satellite was launched," Fasullo said. "This study is a great example of how computer models can give us the historical context that's needed to understand some of what we're seeing in the satellite record."

Understanding whether the rate of is accelerating or remaining constant is important because it drastically changes what sea levels might look like in 20, 50 or 100 years.

Because the study's findings suggest that acceleration due to climate change is already under way, the acceleration should become evident in the satellite record in the coming decade, Fasullo said.

Since the original TOPEX/Poseidon mission, newer satellites, including the recently launched Jason-3, will continue to track sea level.

"Sea level rise is potentially one of the most damaging effects of , so it's critical that we understand how quickly it will rise in the future," Fasullo said. "Measurements from Jason-3 will help us evaluate what we've learned in this study and help us better plan for the future."

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Climate change already accelerating sea level rise, study finds

Journal information: Scientific Reports

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Aug 26, 2016
Seems that the dire effects of Global Warming that were predicted years ago are always 'masked' by something. I guess that's one way to keep the scam going.

Aug 26, 2016
This is what "science" has come to. Instead of looking at the data to see what it says, they torture it to make it say what they want. There is no "acceleration" in sea level rise in the data and the only place they can manufacture it is in computer models that are terrible at simulating global climate. The IPCC's latest report in 2013, AR5, shows how bad the computer models are at projecting future temperatures compared to measured temperatures:


In both tide gauge and satellite measurements, there is no acceleration in sea level rise anywhere. See NASA's sea level graphs here:


The upper (satellite) graph says 3.5 mm/yr and the lower (tide gauge) graph works out to 1.5 mm/yr. They overlap between 1993 and 2000. No acceleration, just different rates due to differences between tide gauges and satellites.

Aug 27, 2016
Ask the Deniers if they have a thermometer.

Aug 27, 2016
My friend who can do DE - told me that this represented acceleration.

Does this friend go on 2 day, 1200 mile jaunts like you?
Does he know that's over half a ton of CO2 and over 10% of the annual average of 4.7 tons?
Does he have no shame, like you?
Is he a retard, like you?

Aug 27, 2016
Ask anti if "he has, at long last, any sense of decency".

Aug 27, 2016
Electric heat is a juice-sucker. If I lived in cold country, I might not have an EV yet.

Aug 27, 2016
What about all of the other large volcanic events which have taken place prior to Pinatubo? Is the contention that they also masked SLR in the long term? If this were true, then these scientists would not have to wait another decade for their results as they should be able to observe the changes that occurred after Novarupta went off in the early 1900s. Then there were also the significant eruptions at Mt Agung, and El Chichon in the 1960s and 1980s. If the above premise was correct, then looking back at these earlier eruptions should add to their story.

Aug 27, 2016
What fools you deniers are.

Electricity -- 63 kWh/month
Gas -- 0
Honda Civic -- < 2000 km/annum

So, next time you start braying CO2 is going to kill us, perhaps (and I know you won't) take a look at your hypocritical Chicken Little retard self.

Aug 27, 2016
What about all of the other large volcanic events which have taken place prior to Pinatubo?

Well before the recent Mt. Pinatubo eruption I used to sumarize climate change this way: Every year the planet gets warmer, then there is a major volcanic eruption. Lather, rinse, repeat.

If you eliminate the major volcanic eruptions effect on global temperatures, you can get ridiculous numbers, for example showing 1910 as warmer than 1810. There were two huge eruptions in the 1800s, Tambora in 1815, and Krakatoa in 1883. Tamboro was a VEI 7, Krakatoa a VEI 6. There were 3 VEI 6 eruptions (including Mt Pinatubo) in the twentieth century. Either we were just unlucky or VEI 6 eruptions occur more often than currently predicted.

The question is when the next VEI 8 event will occur. These sites are not mountains but craters. If you have been to Yellowstone, most of the National Park is inside the caldera from the last time it erupted. A VEI 8 event can cause an ice age...

Aug 28, 2016
When projections don't pan out try to find an excuse.

Aug 29, 2016
nice comment eachus
I suppose we don't have the data to look at what the average ( + standard deviation ...) effect of volcanic ash is.
I hope the C Roads climate simulator will get the improvements/upgrades it needs to allow us to use it to do some comparisons and use our own/other assumptions.

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