Sea level rise: what has happened so far

By: Dr. Jeff Masters , 2:05 PM GMT on June 10, 2009

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Sea level has been rising globally since the late 1700s. This rise has accelerated in recent decades, thanks to increased melting of glaciers and ice sheets due to a warmer climate, plus the fact that warmer oceans are less dense and expand, further increasing sea level. Though sea level rise appears to have slowed over the past five years, it will significantly accelerate if the climate warms the 2 - 3°C it is expected to this century. If these forecasts of a warmer world prove accurate, higher sea levels will be a formidable challenge for millions of people world-wide during the last half of this century. Sea level rise represents one of my personal top two climate change concerns (drought is the other). I'll present a series of blog posts over the coming months focusing on at-risk areas in the U.S., Caribbean, and world-wide. Today, I focus on the observed sea level rise since the Ice Age.

What's at stake
Higher sea levels mean increased storm surge inundation, coastal erosion, loss of low-lying land areas, and salt water contamination of underground drinking water supplies. About 44% of the Earth's 6.7 billion people live within 150 km (93 miles) of the coast, and 600 million people live at an elevation less than ten meters (33 feet). Eight of the ten largest cities in the world are sited on the ocean coast. In the U.S., the coastal population has doubled over the past 50 years. Fourteen of the twenty largest urban centers are located within 100 km of the coast, and are less than ten meters above sea level (McGranahan et al., 2007). The population of many vulnerable coastal regions are expected to double by 2050, according to the U.S. Census Bureau.

Sea level rise since the Ice Age
Before the most recent Ice Age, sea level was about 4 - 6 meters (13 - 20 feet) higher than at present. Then, during the Ice Age, sea level dropped 120 meters (395 ft) as water evaporated from the oceans precipitated out onto the great land-based ice sheets. The former ocean water remained frozen in those ice sheets during the Ice Age, but began being released 12,000 - 15,000 years ago as the Ice Age ended and the climate warmed. Sea level increased about 115 meters over a several thousand year period, rising 40 mm/year (1.6"/yr) during one 500-year pulse of melting 14,600 years ago. The rate of sea level rise slowed to 11 mm/year (0.43"/yr) during the period 7,000 - 14,000 years ago (Bard et al., 1996), then further slowed to 0.5 mm/yr 6,000 - 3,000 years ago. About 2,000 - 3,000 years ago, the sea level stopped rising, and remained fairly steady until the late 1700s (IPCC 2007). One exception to this occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present (Grinsted et al., 2008). This was probably the highest the sea has been since the beginning of the Ice Age, 110,000 years ago. There is a fair bit of uncertainty in all these estimates, since we don't have direct measurements of the sea level.


Figure 1. Global sea level from 200 A.D. to 2000, as reconstructed from proxy records of sea level by Moberg et al. 2005. The thick black line is reconstructed sea level using tide gauges (Jevrejeva, 2006). The lightest gray shading shows the 5 - 95% uncertainty in the estimates, and the medium gray shading denotes the one standard deviation error estimate. The highest global sea level of the past 110,000 years likely occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present. Image credit: Grinsted, A., J.C. Moore, and S. Jevrejeva, 2009, "Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD", Climate Dynamics, DOI 10.1007/s00382-008-0507-2, 06 January 2009.

Sea level rise over the past 300 years
Direct measurements of sea level using tide gauges began in Amsterdam in 1700. Additional tide gauges began recording data in Liverpool, England in 1768 and in Stockholm, Sweden in 1774. These gauges suggest that a steady acceleration of sea rise of 0.01 mm per year squared began in the late 1700s, resulting in a rise in sea level of 2.4" (6 cm, 0.6 mm/yr) during the 19th century and 7.5" (19 cm, 1.9 mm/yr) during the 20th century (Jevrejeva et al., 2008). There is considerable uncertainty in just how much sea level rise has occurred over the past few centuries, though. Measuring global average sea level rise is a very tricky business. For starters, one must account for the tides, which depend on the positions of the Earth and Moon on a cycle that repeats itself once every 18.6 years. Tide gauges are scattered, with varying lengths of record. The data must be corrected since land is sinking in some regions, due to pumping of ground water, oil and gas extraction, and natural compaction of sediments. Also, the land is rising in other regions, such as Northern Europe, where it is rebounding from the lost weight of the melted glaciers that covered the region during the last Ice Age. Ocean currents, precipitation, and evaporation can cause a 20 inch (50 cm) difference in sea level in different portions of the ocean. As a result of all this uncertainty, the 1996 Intergovernmental Panel on Climate Change (IPCC) report gave a range of 4 - 10" (10 - 25 cm) for the observed sea level rise of the 20th century. The 2007 IPCC report narrowed this range a bit, to 5 - 9" (12 - 22 cm), or 1.2 - 2.2 mm/year. Rates of sea level rise are much higher in many regions. In the U.S., the highest rates of sea-level rise are along the Mississippi Delta region--over 10 mm/yr, or 1 inch/2.5 years (USGS, 2006). This large relative rise is due, in large part, to the fact that the land is sinking.


Figure 2. Absolute sea level rise between 1955 and 2003 as computed from tide gauges and satellite imagery data. The data has been corrected for the rising or sinking of land due to crustal motions or subsidence of the land, so the relative sea level rise along the coast will be different than this. The total rise (in inches) for the 48-year period is given in the top scale, and the rate in mm/year is given in the bottom scale. The regional sea level variations shown here resulted not only from the input of additional water from melting of glaciers and ice caps, but also from changes in ocean temperature and density, as well as changes in precipitation, ocean currents, and river discharge. Image credit: IPCC, 2007

Sea level rise over the past 15 years
According to the Intergovernmental Panel on Climate Change (IPCC) 2007 report, sea level accelerated from the 1.2 - 2.2 mm/yr observed during the 20th century to 3.1 mm/year during the period 1993 - 2003. These estimates come from high resolution measurements from satellite radar altimeters, which began in 1992. Tide gauges showed a similar level of sea level rise during that ten-year period. The IPCC attributed more than half of this rise (1.6 mm/yr) to the fact that the ocean expanded in size due to increased temperatures. Another 1.2 mm/yr rise came from melting of Greenland, West Antarctica, and other land-based ice, and about 10% of the rise was unaccounted for. However, during the period 2003 - 2008, sea level rise slowed to 2.5 mm/year, according to measurements of Earth's gravity from the GRACE satellites (Cazenave et al., 2008). This reduction in sea level rise probably occurred because ocean sea surface temperatures have not warmed since 2003 (Figure 3). The authors concluded that sea level rise due to ocean warming decreased more than a factor of five from 2003 - 2008, compared to 1993 - 2003, contributing only 0.3 mm/yr vs. the 1.6 mm/yr previously.


Figure 3. Global average sea surface temperatures (SSTs) from 1990-2008. SSTs have not increased in the past seven years. Image credit: NASA/GISS.

For more information
The best source of information I found while compiling my sea level pages was the Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region report by the U.S. Climate Science Program. It has a huge number of references to all the latest science being done on sea level rise.

References
Bard, E., et al., 1996, "Sea level record from Tahiti corals and the timing of deglacial meltwater discharge", Nature 382, pp241-244, doi:10.1038/382241a0.

Cazenave et al., 2008, "Sea level budget over 2003-2008: A reevaluation from satellite altimetry and Argo", Global and Planetary Change, 2008; DOI:10.1016/j.gloplacha.2008.10.004

Grinsted, A., J.C. Moore, and S. Jevrejeva, 2009, "Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD", Climate Dynamics, DOI 10.1007/s00382-008-0507-2, 06 January 2009.

IPCC (Intergovernmental Panel on Climate Change), 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, UK, and New York, 996 pp.

Jevrejeva, S., J.C. Moore, A. Grinsted,, and P.L. Woodworth, 2008, "Recent global sea level acceleration started over 200 years ago?", Geophysical Research Letters, 35, L08715, doi:10.1029/2008GL033611, 2008.

McGranahan, G., D. Balk, and B. Anderson, 2007, "The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones", Environment & Urbanization, 19(1), 17-37.

Moberg, A., et al., 2005, "Highly variable northern hemisphere temperature reconstructed from low- and high-resolution proxy data", Nature 433, pp613-617, doi:10.1038/nature03265.

United States Geological Survey (USGS), 2006, National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast, U.S. Geological Survey Open-File Report 00-179.

Tropical update
The tropical Atlantic is quiet, and the only region worth watching is the Western Caribbean, which could see formation of a tropical disturbance with heavy thunderstorm activity this weekend.

Jeff Masters

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1481. Levi32
Quoting Patrap:
Best Overall in performance.


It has also been my model of choice for the past week for our current situation in the Caribbean. It has been very consistent. If I had to pick a model to worship it would be the European, but of course I don't do that.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting Patrap:
National Hurricane Center Forecast Verification




Opinions: What Hurricanes were the best predicted track furthest out....I know Ike hit within 100 miles pretty far out...even Andrew was well predicted...
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1478. Patrap
ECMWF is king, and I think will be for a while.


Best Overall in performance.
Member Since: July 3, 2005 Posts: 428 Comments: 129780
1477. Ossqss
Patrap, those graphs tell quite the tale :)

Member Since: June 12, 2005 Posts: 6 Comments: 8188
1476. Levi32
Quoting Patrap:


ECMWF is king, and I think will be for a while.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Hey, any of you meteorologist out there Yahoo main page news says some organization is trying to classify a new type of cloud past the existing 3. They have a picture attached to the story if anyone wants to look.
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1473. Patrap
Member Since: July 3, 2005 Posts: 428 Comments: 129780
1472. Patrap
Member Since: July 3, 2005 Posts: 428 Comments: 129780
1471. Patrap
National Hurricane Center Forecast Verification



Member Since: July 3, 2005 Posts: 428 Comments: 129780
1470. Levi32
Quoting scottsvb:
Remember the Nogaps had this going up thru S florida and the Bahamas a week ago by now...its always hit and miss..just slightly better than the GEM.



In its defense....all the models that saw the low did the same thing. Most of the models have an eastward bias with forming systems and after all it was a week ago. It's rare they get the track ideas right a week and a half in advance.

That said....the NOGAPS is usually inconsistent, but I take note when it's in consensus with a couple other models.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Drake's picture and Levi's go together looks like 1/2 eye where Levi Low was located.
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Remember the Nogaps had this going up thru S florida and the Bahamas a week ago by now...its always hit and miss..just slightly better than the GEM.

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1467. Levi32
Quoting IKE:
18Z NOGAPS takes a strong vort into the Yucatan and then SE Texas.


The NOGAPS isn't as fast with the system as the GFS but still too fast.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
1466. Drakoen
Quoting IKE:
18Z NOGAPS takes a strong vort into the Yucatan and then SE Texas.


It pretty much washes out as it advects into the westward GOM.
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Quoting TampaSpin:


That is exactly where i'm at....great part of Tampa!

Very pretty area with the Cypress trees and such...low lying though...
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1464. IKE
18Z NOGAPS takes a strong vort into the Yucatan and then SE Texas.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Most of the disturbed weather across the caribbean should stay south of the florida through the up coming weeekend so outside of the low 90's it should be a nice.The spin to the east of southern florida is in the upper levels and no development is anticipated.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
Quoting clwstmchasr:
Westchase is one of my favorite golf courses.


LOL better hit them straight there as it Narrow and woods and water...bring lots of balls if one does not hit it straight....LOL
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Quoting TampaFLUSA:

I want to move to the NW part of the county or in the Palm harbor Safety Harbor area...


That is exactly where i'm at....great part of Tampa!
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Quoting TampaSpin:


Near Alonso High School......in West Chase...

I want to move to the NW part of the county or in the Palm harbor Safety Harbor area...
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1458. gator23
Quoting weathermanwannabe:
As mentioned earlier, Wilma was memorable because the warm "swamp" water in the Everglades area did not slow her down/reduce intensity as she crossed it from Florida Bay accross that narrow band of Florida and out accross to the East Coast around Fort Lauderdale/Palm Beach so the intensity level after "landfall" caught folks by surprise..


Thats typical of many south florida storms. Fay for example strenghtend as she crossed
Member Since: August 26, 2008 Posts: 0 Comments: 2182
Quoting TampaFLUSA:

What part of the area are you in? I'm temporarily in N Tampa...


Near Alonso High School......in West Chase...
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Quoting Ossqss:


Just to help out since he said he can't see ya :)


lol I caught that
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1455. Levi32
Quoting TampaSpin:


Your 100% correct...Secondly the Low in place is not uncommon as a stationary Low know as the Columbian Low....which i would rather have a HIGH.....LOL


It's usually over land or very near the coast....but yes this mess was basically born from the Columbian low as it was drawn northward by the TUTT and the tropical wave that passed through the area.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
The tropical wave in the Central Atlantic looks quite healthy, and there is some vorticity associated with it. Despite the high shear, a deformation zone is what seems to help it maintain its convection. It will be quite interesting what happens what happens when it moves away from the deformation zone. Albeit shear will decrease, it will have to rely solely on itself for convection.


I have been tracking blobs in the SW Caribbean for almost 2 weeks now, and I've had it! lol
Member Since: July 19, 2008 Posts: 43 Comments: 4051
1453. Ossqss
The loooooonnnnnggggg range GFS shows something on the 27th :-----P

Link
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting Levi32:


The blob was simply a result of the diffluent flow on the east side of the upper trough.....one must realize that the center of the broad area of low pressure is north of Panama, and the "blob" is not significant.



Who says a new low pressure area won't form with the associated deep convection if/when shear drops though...this broad area of lower pressure is just stationary.
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Quoting TampaSpin:


Nothing in the Caribbean YET to worry about. The one that might eventually come together is outside the Islands.....


What part of the area are you in? I'm temporarily in N Tampa...
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Quoting Levi32:


The blob was simply a result of the diffluent flow on the east side of the upper trough.....one must realize that the center of the broad area of low pressure is north of Panama, and the "blob" is not significant.



Your 100% correct...Secondly the Low in place is not uncommon as a stationary Low know as the Columbian Low....which i would rather have a HIGH.....LOL
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1449. Levi32
Quoting TampaSpin:
Back from my run......WOW the Caribbean blob went poof real fast...


The blob was simply a result of the diffluent flow on the east side of the upper trough.....one must realize that the center of the broad area of low pressure is north of Panama, and the "blob" is not significant.

Member Since: November 24, 2005 Posts: 635 Comments: 26700
1448. Drakoen
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1447. Ossqss
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting foggymyst:
Hello to all.. Hi Tampa.. have not been in a week or so. Can anyone give me an update on the blob I have been reading about? Thanks.


Nothing in the Caribbean YET to worry about. The one that might eventually come together is outside the Islands.....

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Thanks!
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As mentioned earlier, Wilma was memorable because the warm "swamp" water in the Everglades area did not slow her down/reduce intensity as she crossed it from Florida Bay accross that narrow band of Florida and out accross to the East Coast around Fort Lauderdale/Palm Beach so the intensity level after "landfall" caught folks by surprise..
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1442. Ossqss
The blob is taking a break for the day.

Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting Ossqss:
How true Pat, perhaps those who desire the canes would take a different perspective if they had the knowledge from being in one. Having seen the leftovers from Andrew and Charley soon after their impact, makes my hair stand up and knees shudder every time I think of it. I would prefer no canes, but Mother Nature has a different opinion.


I grew up in Miami from 1961 to 1973 and experienced my share of bad hurricanes. After I moved to Grand Cayman I got tired of hearing Caymanians saying they hope a hurricane would hit so they could see what it was. I always told them don't wish for that and I bet since Ivan no more of that kind of talk. No-one who hasn't been through one knows the destruction it causes.
Member Since: October 9, 2008 Posts: 0 Comments: 8436
Where????....LOL

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1439. gator23
Quoting WPBHurricane05:
LOL...just reading some post's on the last page and someone doesn't think Wilma made a direct hit in West Palm Beach??

So the calm winds I experienced for about 30 minutes in between 100+ mph winds was just a break in the weather?


HAHAH!
Member Since: August 26, 2008 Posts: 0 Comments: 2182
Hello to all.. Hi Tampa.. have not been in a week or so. Can anyone give me an update on the blob I have been reading about? Thanks.
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Quoting FlaPuertoRico2:
Hi! How come I can't see Acemmett90 comments or some others? Is it that they are not popular? How can I fix?

Not popular..click show all above.
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1436. Ossqss
Quoting Acemmett90:

go to filter then select show all


Just to help out since he said he can't see ya :)
Member Since: June 12, 2005 Posts: 6 Comments: 8188
1435. Patrap
Maximum Potential Hurricane Intensity


The maps display potential minimum pressure and maximum winds, calculated according to a method developed by Dr. Kerry Emanuel. Dissipative heating is handled according to a method described in Bister and Emanuel (1998). The maps are based on data from the 00Z global operational analysis from NCEP for the date shown on the plot. The top panel shows the potential minimum central pressure for a hurricane at any given location (in millibars). Only values less than 1000mb are shaded. Cyan squares indicate grid points where the algorithm failed to converge. Also shown are the sea surface temperatures (°C). The bottom panel shows the potential maximum wind speed expressed in terms of the type and severity of storm they would represent (TD = Tropical Depression, TS = Tropical Storm, H1-H5 = Hurricanes of category 1-5 on the Saffir-Simpson scale).


Member Since: July 3, 2005 Posts: 428 Comments: 129780
Hi! How come I can't see Acemmett90 comments or some others? Is it that they are not popular? How can I fix?
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1432. Patrap
No doubt Levi..if the entity slips under the High and her engine is up and running,well the TCHP is there ..
Member Since: July 3, 2005 Posts: 428 Comments: 129780

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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