Sea Level Rise Accelerating

[LocoAko]

Original paper: http://www.pnas.org/content/early/2011/06/13/1015619108.abstract

http://www.scientificamerican.com/article.cfm?id=warming-accelerates-us-east-coast-sea-level

Warming Accelerates Sea Level Rise on U.S. East Coast

A new study finds that sea levels are creeping up faster along the coast of North Carolina thanks to climate change

By Lauren Morello and ClimateWire | June 21, 2011 | 3

Sea level is rising faster along the U.S. East Coast than it has for at least 2,000 years, according to new research.

The ocean began rising an average of 2.1 millimeters per year some time between 1865 and 1892 and hasn't stopped, the study concludes. The current rate of sea level rise is about 3.2 mm per year.

That trend, gleaned from muck collected in North Carolina salt marshes, is a direct consequence of increasing temperatures, said co-author Benjamin Horton, a coastal geologist at the University of Pennsylvania.

"We can see climate-related patterns," he said. "We can see our hypothesis that as temperature goes up, sea level goes up."

The reverse is also true, according to the research, which shows temperatures and sea levels rising and falling in lockstep for at least the last 1,000 years. The findings will be published online this week by the Proceedings of the National Academy of Sciences.

Peter Clark, a geologist at Oregon State University, said the new study represents a "significant advance" because it extends the record of sea level rise back two millennia, giving scientists a better context for current sea level rise.

"It's important to learn about past climate (and sea level) because we want to know how it varies naturally (i.e., when there was no possible human influence) so as to evaluate whether the current recent changes are unusual," he said in an email.

The new paper does "firmly establish" that current sea level rise is unprecedented for the recent past, said Ken Miller, a geologist at Rutgers University. The work was warmly received last year when the authors presented it at a sea level-rise workshop sponsored by the Intergovernmental Panel on Climate Change, he said.

Period of stability to A.D. 950

In addition to the recent sea level rise, the record pieced together by Horton's team shows a long period of stable sea level from 100 B.C. to A.D. 950. That marked the beginning of a warm period that lasted roughly four centuries, a time when seas rose 0.6 mm per year. Sea level then held steady, or slightly fell, until the late 19th century, when the current sea level spike began.

"When temperatures really rocketed as they did in the 20th century," Horton said, "our sea levels did the same."

Scientists have good measurements of recent sea level rise from a combination of tide gauges, which began collecting data in the early 20th century, and satellites, which started tracking sea level in 1992.

To go even further back in time and put recent conditions in context, the authors of the new study examined sediment samples from North Carolina salt marshes.

Those marshes are "an ideal natural laboratory," Horton said, because they are always slowly sinking and being rebuilt as tides wash in new sediment. That steady accumulation of muck traps tiny organisms called foraminifera, plant matter and other substances that form a natural record of sea level rise.

The scientists began decoding that record by mapping the distribution of different foraminifera species -- or "forams" -- at 10 North Carolina marsh sites.

A marsh is typically home to several species of forams, which each prefer slightly different conditions. Some thrive in the relatively fresh water found in areas that aren't often inundated by ocean tides, while others seek out a saltier brew.

Understanding which foram species were found in areas often overtopped by salt water and which weren't allowed scientists to construct a model they used to analyze sediment cores from two marshes and estimate sea level rise over time.

Peering back two millennia meant collecting cores 3 to 4 meters long. Extracting information about sea level required cutting those cores into 1-centimeter chunks and analyzing the foram fossils found in those chunks.

Dating sediments using ragweed and nuclear fallout

The researchers determined the age of each chunk by carbon dating, possible because the sediment is rich in decomposed plant matter. They honed those estimates further by examining the chunks for the first signs of ragweed pollen, which settlers introduced to the area in 1720, and the cesium and lead fallout from atomic bomb testing in the 1950s.

Finally, Horton's team subtracted the annual rate of subsidence from the sea level rise pattern they reconstructed from the sediment samples. That left them with a record of the sea level caused by climate variations.

The technique isn't new, but the new study marks the longest continuous record produced from sediment samples, Horton said.

That understanding of the past will help scientists improve their models of future sea level rise, he said, by allowing them to test models' ability to simulate the known conditions of the past -- a technique known as "hindcasting."

"If you are tuning a model to just the 20th-century data, all you have is sea level rising," Horton said. "It's very hard to tune a model when it's just unidirectional."

Still, that doesn't mean the exact relationship between temperature and sea level rise evident in the salt marsh data will hold as climate change accelerates in the future, Miller cautioned.

The processes that drive the behavior of the world's ice sheets may be different in intensity or type than those that drove melting in the past, he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

[Clifford]

Here is a link to the paper.

http://wattsupwiththat.files.wordpress.com/2011/06/pnas_kemp-etal_2011_sea_level_rise.pdf

So, not surprising there was an increase in the rate of sea level rise from about 1000 to 1500 AD corresponding to the Medieval Warm Period, and fall in sea levels around 1600 corresponding to the Marauder Minimum.

The Atlantic Sea Level has also been rising for a very long time, although there does appear to be a slight acceleration over the last century or so.

There is a risk, however, of attributing too much to sea level changes in a few locations as the measurements are often confounded by land subsidence and changes in silt deposition caused by dams, flood control, and water distribution changes.

Keep in mind that most measurements indicate a slight fall in global sea levels in 2011. Presumably only a short-term change, but only time will tell.

[nzucker]

The fact that sea level rise in the East Coast started in the 1860s suggests that much of this was a response to recovery from the Little Ice Age (Dalton/Maunder Minima)....it may have been accelerated some by anthropogenic warming, but the start of the phenomenon was long before mass releases of carbon dioxide from industry and transportation. We didn't even have the Bessemer process to create large quantities of steel in the 1860s, and the Civil War put a huge dent in American manufacturing of consumer goods that might have contributed to the amounts of CO2 we release today.

[skierinvermont]

The fact that sea level rise in the East Coast started in the 1860s suggests that much of this was a response to recovery from the Little Ice Age (Dalton/Maunder Minima)....it may have been accelerated some by anthropogenic warming, but the start of the phenomenon was long before mass releases of carbon dioxide from industry and transportation. We didn't even have the Bessemer process to create large quantities of steel in the 1860s, and the Civil War put a huge dent in American manufacturing of consumer goods that might have contributed to the amounts of CO2 we release today.

Had it not been for AGW, global temps would have continued to fall after the 1940s and SLR would have dropped. Instead, temperature and SLR have accelerated upwards.

[tacoman25]

Had it not been for AGW, global temps would have continued to fall after the 1940s and SLR would have dropped. Instead, temperature and SLR have accelerated upwards.

Accelerated from 2.2 mm/year in the late 1800s to 3.3 mm/year now, per that study. 1 mm/year now more than then.

[skierinvermont]

Accelerated from 2.2 mm/year in the late 1800s to 3.3 mm/year now, per that study. 1 mm/year now more than then.

Indeed. Which makes for the most rapid period of sea level rise over a 100 year period in the last 2,000 years by far. Had sea levels risen from 1860-1940 and then plateaued or declined slightly, the increase would have been fairly mundane and would have fit in with the natural oscillations that have occurred over the last 2,000 years. What makes this period of warming and rising oceans unique in the last 2,000 years is the rapidity and duration for which it has occurred. The temperature is already probably at unprecedented levels for the last 2,000 years, and sea level will soon surpass the highest levels of the last 2,000 years.

[ORH_wxman]

This is an interesting peer reviewed study (from 2011) that shows how sea level rise has not been accelerating at all in the 20th century and even into the 21st century...instead actually slightly decelerating since 1930.

http://www.jcronline...ES-D-10-00157.1

[skierinvermont]

This is an interesting peer reviewed study (from 2011) that shows how sea level rise has not been accelerating at all in the 20th century and even into the 21st century...instead actually slightly decelerating since 1930.

http://www.jcronline...ES-D-10-00157.1

Yep .. there certainly was a strong surge in sea level coming out of the cold 1800s from 1880-1940. It isn't supposed to accelerate too much until the GIS destabilizes.

[tacoman25]

Yep .. there certainly was a strong surge in sea level coming out of the cold 1800s from 1880-1940. It isn't supposed to accelerate too much until the GIS destabilizes.

How do you reconcile this with what you said earlier?

Had it not been for AGW, global temps would have continued to fall after the 1940s and SLR would have dropped. Instead, temperature and SLR have accelerated upwards.

[skierinvermont]

How do you reconcile this with what you said earlier?

There isn't supposed to be that much acceleration.. maybe some but sea level rise is hard to predict.. and we've seen a bit of acceleration in the last couple decades. That is the acceleration I was referring to (3.5mm/yr over the last 20 years). The real acceleration comes when the greenland ice sheet destabilizes.

[tacoman25]

There isn't supposed to be that much acceleration.. maybe some but sea level rise is hard to predict.. and we've seen a bit of acceleration in the last couple decades. That is the acceleration I was referring to (3.5mm/yr over the last 20 years). The real acceleration comes when the greenland ice sheet destabilizes.

Maybe, but as you pointed out, the error bars allow the possibility that there has been no acceleration at all. It just seemed odd that in one post you were saying AGW was supposed to lead to faster sea level rise since the 1940s (and was), and in another post you were saying it wasn't.

[skierinvermont]

Maybe, but as you pointed out, the error bars allow the possibility that there has been no acceleration at all. It just seemed odd that in one post you were saying AGW was supposed to lead to faster sea level rise since the 1940s (and was), and in another post you were saying it wasn't.

Well not really.. the 20th century was 2.5mm/yr (I think), while the last 20 years have been 3.5 +/- .4mmy/yr which is definitely higher.

[tacoman25]

Well not really.. the 20th century was 2.5mm/yr (I think), while the last 20 years have been 3.5 +/- .4mmy/yr which is definitely higher.

But that 2011 study that ORH cited said there had been deceleration since the 1930s...

[BethesdaWX]

This is an interesting peer reviewed study (from 2011) that shows how sea level rise has not been accelerating at all in the 20th century and even into the 21st century...instead actually slightly decelerating since 1930.

http://www.jcronline...ES-D-10-00157.1

Basically the Point. Sea Level rise has, overall, remained at an Unchanged rate since the end of the LIA. Of course before 1950 it is due Natural Causes, and after 1950 it is due to AGW.....

[salbers]

Looks like an interesting well-written paper that ORH mentions. As the paper suggests, one important question is how to resolve any divergence between tide gauges and satellite altimetry over the past 10-20 years.