Posts Tagged ‘sea level rise rate’

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The Search for Acceleration, part 6, Australia

July 17, 2013

magnifying glass 145This is part 6 of a series of posts in which I am searching for a large acceleration in sea level rise rate in the latter part of the 20th century that could reconcile the 1.8 mm per year average rise rate for the century attributed to tide gauge data and the approximately 3 mm per year rise rate for the tail end of the century attributed to the satellite data.

Australia

Australia has only 5 tide gauge stations with data sets that are at least 90% complete going back to 1960, but four of those go back to 1940 or earlier.  I will analyse this data in my usual way (detrend, weight, average, and derivative).

Regional sea level rise rates are usually swamped by things other than just global effects.  In the case of Australia we may be able to disentangle one of these effects – the El Nino Southern Oscillation.  I will also consider the component of the Australian sea level data that is orthogonal to the ENSO3.4 sea surface temperature.

The slide show shows my standard analyse.

This slideshow requires JavaScript.

ENSO

The El Nino Southern Oscillation dominates the sea level around Australia.  The following plot shows an overlay of the detrended weighted average of the five Australian tide gauge sites and the NINO3.4 index from the Hadley Centre.  I am including tide gauge data after 1915 which include at least two tide gauge sites at all times and no large data gaps.  The similarities are obvious.

ENSO sea level overlay

Let’s try to remove the ENSO effect from the sea level around Australia. I will do that by breaking the sea level data down into an ENSO correlated and ENSO orthogonal parts. If the ENSO orthogonal part of the sea level is truly independent of ENSO, then it shows what the sea level around Australia would look like without an ENSO effect.  Here is the formula for finding the ENSO orthogonal component of the of the sea level data.

orthogonal formula440

The top of each of the following slides shows the weighted, detrended, averaged Australian sea level (white), ENSO3.4 sea surface temperature (blue),  and the component of sea level data that is orthogonal to the ENSO3.4 data (red).  The bottom of each slide shows the corresponding relative rise rates associated with sea level (white) and with the ENSO orthogonal component of the sea level (red).  Each successive slide shows the same original data with increasing Gaussian smoothing.

The most important thing to notice is that when the ENSO influence is removed the sea level rise rate at the end of the century is significantly reduced.

ENSO and global warming

If the higher relative rise rates at the end of the century are due to ENSO, then it is interesting to ask whether ENSO fluctuations are greater now (because of global warming?) than in the past.  The best answer to this question can be found in Highly Variable El Niño-Southern Oscillation Throughout the Holocene (Cobb, et. al., Science, 339, 1/4/13).

The abstract states…

Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

and the body of the paper mentions…

[T]he detection (and attribution) of any changes in ENSO properties would require very long time series spanning many centuries, to the extent that detection of such changes is even possible.

[M]uch of the observed differences in ENSO variance over the past 7 ky reflect strong internal variability… Relatively robust 20th-century ENSO variability may reflect a sensitivity to anthropogenic greenhouse forcing, but definitive proof of such an effect requires much longer data sets than are currently available, given the large range of natural ENSO variability implied by the available fossil coral data.

Conclusion

According to my usual analysis the rise rate at the end of the century was clearly higher than the average (from 1940 to present), but no higher than the 1940s.   Does the reconcile the satellite data and tide gauge data?  Yes.

But, when the part of the detrended sea level that is correlated to ENSO3.4 is removed, the remaining orthogonal part of the rise rate appears to be lower at the end of the century than during the 1940s, and not particularly high compared to the rest of the century. So if my removal of the ENSO effect is correct, then there was nothing “unusual” about the rise rate at the end of the century
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Sources

20th century rise rate average of 1.8 mm/year

1. Church and White Global Mean Sea Level Reconstruction

2. Links to Church and White sea level data

Satellite data (about 3 mm/year): CU Sea Level Research Group

RLR tide gauge data: Permanent Service For Mean Sea Level

ENSO/Global warming relationship: Cobb, et. al., Science, 339, 1/4/13

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The Search for Acceleration, part 5, The Netherlands

July 6, 2013

magnifying glass 145This is part 5 of a series of posts in which I am searching for a large acceleration in sea level rise rate in the latter part of the 20th century that could reconcile the 1.8 mm per year average rise rate for the century attributed to tide gauge data and the approximately 3 mm per year rise rate for the tail end of the century attributed to the satellite data.

The global sea level rise rate is swamped by other effects.  In most locations the yearly rise and fall of the oceans is greater than the 18 cm of sea level rise during the entire 20th century.  Geologic effects (e.g. glacial isostatic adjustment or plate tectonics) add to local and regional rise rates, making them deviate greatly from the global rise rate.

I am working under the theory that by detrending sea level data from individual (local) sites and averaging with other regional sites it should be possible to extract changes in regional sea level rise rates while bypassing the question of what the “true” sea level rise rate is in that region.

The Netherlands

Netherlands elevation

Elevation and tide gauge locations for The Netherlands.

Nobody cares more about sea level rise than the folks in The Netherlands. They have been dealing with the issue long before anybody was worried about global warming, since 20% of the country’s area is below sea level.  They have excellent sea level data spanning nearly 150 years.  This map shows land elevations in the Netherlands as well as the location of seven high quality tide gauge stations.

Here is the PSMSL data for those seven locations…

Netherlands Raw Spread

Tide gauge data for the Netherlands.

As I have mentioned before, I am not concerned with finding the sea level rise rate, but rather the change in sea level rise rate. But this set of data averages out to have a 20th century rise rate very close to the commonly reported tide gauge derived average of 1.8 mm/year. (Click on image if animation does not advance.)

sea level annotated 450ani

These seven stations also have very coherent yearly signals, created from the 2, 3, 4, 6 & 12 month Fourier components.  Note that the magnitude of the yearly signal is nearly the same as the entire average sea level rise for the entire 20th century.

Netherlands Yearly signal

Now, lets consider the weighted, detrended data to derive the relative acceleration. (Click on image if animation does not work.)

Netherlands weighted and detrened 450ani

Conclusion

The Netherlands tide gauge data if of the highest quality and long duration.  All seven stations cover 1870 to the present.  The detrended sea level rise rate does indicate that the overall sea level rise rate for last two decades of the 20th century was a few mm per year greater than the century’s average.  However, this very reliable data also indicates that the sea level rise rate at the beginning of the century was just as high as the end of the century.

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Sources

20th century rise rate average of 1.8 mm/year

1. Church and White Global Mean Sea Level Reconstruction

2. Links to Church and White sea level data

Satellite data (about 3 mm/year)

CU Sea Level Research Group

RLR tide gauge data

Permanent Service For Mean Sea Level

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Cities Underwater: Miami

July 2, 2013

Perhaps the dolts at Rolling Stone should stick to photos of aging rock stars, because they just embarrass themselves when they stray into science and reason.  Their boneheaded article by Jeff Goodell, “Goodbye, Miami” starts out by looking back from some fictitious hurricane in 2030.  This fantasy breathlessly tells us…

“When the water receded after Hurricane Milo of 2030… A dead manatee floated in the pool where Elvis had once swum. Most of the damage occurred not from the hurricane’s 175-mph winds, but from the 24-foot storm surge that overwhelmed the low-lying city.”

Well, at least they snuck in something about a dead rock-n-roller.  They continue…

The storm knocked out the wastewater-treatment plant on Virginia Key, forcing the city to dump hundreds of millions of gallons of raw sewage into Biscayne Bay. Tampons and condoms littered the beaches, and the stench of human excrement stoked fears of cholera. More than 800 people died, many of them swept away by the surging waters that submerged much of Miami Beach and Fort Lauderdale.

Wait!  Don’t the folks at Rolling Stone think “condoms littering the beaches” are a good thing?  I’m confused.

After another paragraph of blather they really get to the point…

But Hurricane Milo was unexpectedly devastating. Because sea-level­ rise had already pushed the water table so high, it took weeks for the storm waters to recede…And still, the waters kept rising, nearly a foot each decade. By the latter end of the 21st century, Miami became something else entirely: a popular snorkeling spot where people could swim with sharks and sea turtles and explore the wreckage of a great American city.

Well now, Mr. Goodell, I can’t decide if you are dishonest or just plain stupid. Anybody who is going to put his fingers to the keyboard to write an article about sea level rise at a particular coastal city would surely look up the sea level data for the region before indulging in such preposterous fantasies.

I’ll help him out.  Here is a list of sea level tide gauge sites in Florida with long and up-to-date records.  Click on any of then to see the sea level plots from the Permanent Service for Mean Sea Level.

Fernandina Beach, Florida: 100 years of data, 2.02 mm/year  (0.8 inches/decade)

Mayport, Florida: 80 years of data, 2.40 mm/year (0.9 inches/decade)

Key West , Florida: 100 years of data, 2.24 mm/year (0.9 inches/decade)

Naples, Florida: 40 years of data, 2.02  mm/year  (0.8 inches/decade)

Fort Myers, Florida:  40 years of data, 2.40 mm/year (0.9 inches/decade)

St. Petersburg, Florida: 60 years of data, 2.36 mm/year (0.9 inches/decade)

Clearwater Beach, Florida: 40 years of data, 2.43 mm/year (1.0 inches/decade)

Cedar Key, Florida: 100 years of data, 1.80 mm/year (0.7 inches/decade)

Apalachicola, Florida:  40 years of data,  1.38 mm/year (0.5 inches/decade)

Panama City, Florida: 40 years of data, 0.75 mm/year (0.3 inches/decade)

Pensacola, Florida: 90 years of data,  2.1 mm/year (0.8 inches/decade)

Look at those numbers.  They don’t exactly look like “nearly a foot each decade,” do they?

OK, Mr. Goodnell, stick with me here – we’re going to do some 5th grade math.  Look at the data above and make an estimate of how much the sea level will rise along the Florida coast by 2030.  How about we go with 2 inches (although that is certainly too high).

Now suppose your fictitious hurricane does bring a “24-foot storm surge.” Oh no!!! with the additional sea level rise that storm surge will be 2 inches higher!!!