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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Testing if my new avatar was approved...
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1531. Ossqss
That is awesome Patrick. Keep doing what you do. I am glad to have met you!
Member Since: June 12, 2005 Posts: 6 Comments: 8186
2009 Hurricane Early Season A Bust! I bet if we all left the blog for 2 weeks, and came back, nothing would have formed during our break.
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Quoting gordydunnot:
Pat your right about radio but most small tv's have radio. I was pointing out that you can watch the eye come ashore on tv and while you usually loss power before the eye gets there the tv stations dont. Weather radio is best no doubt.I was watching tv when Andrew hit I breath a sight of relief before some called the jog south.Plus you can watch the bands for yourself as in the Wilma radar.

With the digital switch u have to have a digital portable tv...even the radios that have "sound only" TVs, that is where u can listen to the TV broadcast only will go off the air.
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Thanks ,Ossgss
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1526. Ossqss
Quoting gordydunnot:
Pat your right about radio but most small tv's have radio. I was pointing out that you can watch the eye come ashore on tv and while you usually loss power before the eye gets there the tv stations dont. Weather radio is best no doubt.I was watching tv when Andrew hit I breath a sight of relief before some called the jog south.Plus you can watch the bands for yourself as in the Wilma radar.


I got one of these Sony items. Runs on 2-C batteries or the hand crank power that goes to two internal NiMH batteries. Works well and is inexpensive.

Link
Member Since: June 12, 2005 Posts: 6 Comments: 8186
1524. Patrap
Nova was the Last of a Line I bred since 89.

And she was Awarded the Same Accolades as I for her work Post Katrina,..though not present in Baton Rouge Dec 1 06,she was mentioned as the Tribute Citation was read,..and that will always be a reminder that even during the Darkest Days,her eyes and ears especially heard many a Cry for Help..
And without her,we may have missed scores of folks.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
Pat your right about radio but most small tv's have radio. I was pointing out that you can watch the eye come ashore on tv and while you usually loss power before the eye gets there the tv stations dont. Weather radio is best no doubt.I was watching tv when Andrew hit I breath a sight of relief before some called the jog south.Plus you can watch the bands for yourself as in the Wilma radar.
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1522. Ossqss
Quoting Patrap:
Nova Von Snowcloud was my German Shepherd who passed Dec 16th 08.
She never left my side for 19days Post K and was instrumental in many respects to the job we were doing post Storm.



Beautiful dog Pat, I am sure Nova is missed very much.
Member Since: June 12, 2005 Posts: 6 Comments: 8186
We must be on the same grid O5
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1520. Ossqss
DTV item from tonight.

Link

Another you may want to look at that I posted earlier. We all will be impacted to some degree.

Link
Member Since: June 12, 2005 Posts: 6 Comments: 8186
1519. Patrap
Nova Von Snowcloud was my German Shepherd who passed Dec 16th 08.
She never left my side for 19days Post K and was instrumental in many respects to the job we were doing post Storm.

Member Since: July 3, 2005 Posts: 423 Comments: 128228
Quoting GeoffreyWPB:
Kinda funny story with me...with Frances and Jeanne, I didn't have power for about a total of a month. With Wilma, which took my roof off, I had power the next day.


Same here basically (minus the roof). Must be a Palm Springs thing.
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Quoting Ossqss:


Going digital tomorrow !

I used an inverter with a deepcycle and small TV. You could inline the converter in that senario.

Pat, what is NOVA?
Isn't that a car?
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1516. Patrap
An Radio is a much better tool than aTV post Storm...

Easily carried and used.
TV from the Local Stations most likely will be down in a Big Cane.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1515. Ossqss
Quoting gordydunnot:
Ossgss good point I was about to say get a small battery powered TV, but I just realize ,what are we going to do now that we are going digital. Someone could make a lot of money or maybe they have I don't know.


Going digital tomorrow !

I used an inverter with a deepcycle and small TV. You could inline the converter in that senario.

Pat, what is NOVA?
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Ossgss good point I was about to say get a small battery powered TV, but I just realize ,what are we going to do now that we are going digital. Someone could make a lot of money or maybe they have I don't know.
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Kinda funny story with me...with Frances and Jeanne, I didn't have power for about a total of a month. With Wilma, which took my roof off, I had power the next day.
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1512. Patrap
During the Storm I had a Car Battery and AM/FM Car Radio and a Speaker in the Attic with me..an NOVA.
In case I was flooded out,at least Id have info.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
We are all worryin about a Carribbean blob, look at the blob approachin the lesser antillies
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1510. Ossqss
Patrap, you still out there?

Just curious, when you were in the eye,assuming you lost power, what did you do for power? Battery operated stuff or inverter etc, to power radio, tv etc.


1508 6-27 :)
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Se Bahamas circulation is the ull. seems to have stopped moving sw.
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I'm starting to agree with some of the bloggers on here that we may not see our first named Atlantic storm until July or perhaps August.
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000
ABPZ20 KNHC 112338
TWOEP
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT THU JUN 11 2009

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

THE AREA OF DISTURBED WEATHER LOCATED ABOUT 900 MILES SOUTHWEST OF
THE SOUTHERN TIP OF BAJA CALIFORNIA HAS NOT BECOME BETTER ORGANIZED
TODAY. THIS SYSTEM IS MOVING NORTH-NORTHWESTWARD AT 10 TO 15
MPH...AND INTO AN ENVIRONMENT LESS CONDUCIVE FOR DEVELOPMENT.
THERE IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH

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1505. Ossqss
Delete all this stuff and it will shrink :)

Hey it worked - all the BR stuff FM.




Member Since: June 12, 2005 Posts: 6 Comments: 8186
1502. They're doing fine with it right now. Nothing imminent.
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.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
000
ABNT20 KNHC 112332
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU JUN 11 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS.

$$
FORECASTER PASCH

Not saying anything against the NHC or anything, but I wonder if they're looking at the disturbance.
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1501. Ossqss
Is that a circulation over the S Bahama's?
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Quoting extreme236:


I feel sorry for the people there...rather poor living conditions+heavy rains always spell major trouble.


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Click on image to view original size in a new window



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Look at this blob approachin the Lesser Antilles Islands.

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1497. Ossqss
You can find anyting on WU.

Link
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Quoting Levi32:


Looks like it will be giving Hispaniola some more heavy rainfall tonight...


I feel sorry for the people there...rather poor living conditions+heavy rains always spell major trouble.
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1495. Drakoen
Quoting Levi32:


I've followed the models for years and the ECMWF in recent history has outdone the GFS despite all the worship the GFS gets from people. They're pretty close in the short-term but the Euro is by far the best in the extended-range.


That would be because the ECMWF has a better resolution.
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Technically, the HWRF is supposed to be superior to the GFS/GFDL as it was meant as a high-resolution upgrade to the GFDL. However, in it's short history it has yet to be very consistent, and has always trended toward outlier situations.
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1493. Levi32
Quoting extreme236:


We'll see.


Looks like it will be giving Hispaniola some more heavy rainfall tonight...
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Quoting Levi32:


Because I promise you this particular "blob" will be gone long before that happens. You need a slow-moving MCC for 12+ hours before you can think of getting a new low-pressure center under it that will actually last a while.


We'll see.
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1491. Patrap
Also,..as the storm closes to the coast,dont focus on the center point as well,by that time track is usually determined..and when the official landfall occurs when the center reaches the coast,Half the Storm is already ashore.
Plan ahead,plan now..have a Plan to be ready.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1490. Levi32
Quoting Drakoen:
Just one year doesn't make the ECMWF the best model I think it's definitely up there with the GFS and the GFDL.


I've followed the models for years and the ECMWF in recent history has outdone the GFS despite all the worship the GFS gets from people. They're pretty close in the short-term but the Euro is by far the best in the extended-range.
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1489. Levi32
Quoting extreme236:


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.


Because I promise you this particular "blob" will be gone long before that happens. You need a slow-moving MCC for 12+ hours before you can think of getting a new low-pressure center under it that will actually last a while.
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1488. Patrap
Hurricane Archive:

All Atlantic Storms (1851-2009):




Member Since: July 3, 2005 Posts: 423 Comments: 128228
1487. Patrap
Those Radar views come from the Archive on the Tropical Page here.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1486. Drakoen
Just one year doesn't make the ECMWF the best model I think it's definitely up there with the GFS and the GFDL.
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Pat it just goes to show you why stormw and other mets. say don't fixate on the line. During Andrew as well as it was forecast I am glad I was in wrong place at the right time.
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1483. brianc
paptrap:
thx so much for Wilma radar link. Living through Wilma in Miami I missed all the radars since the power was lost very early on.... I agree that Wilma was a direct hit for many in S. Fla...when my poured-concrete 14 story condo on Biscayne Bay "swayed" at the storm's peak...it made me appreciate what a Cat.3/4 might be like. (My building, btw, weathered both Betsy '65 and Andrew pretty much intact.)
Wilma was the 3rd costliest storm in US history... and it certainly affected the widest swath of destruction I've ever seen. The eye was 50 miles wide! Everywhere from Boca and parts north to the Keys was blacked out. The only reason Wilma failed to grab greater attention from the national media was because in storm-weary 2005 , Katrina captured the spotlight (and, of course, not w/o due cause). But still...anyone who thinks Wilma wasn't a direct hit had to be dozin' or out of town. In fact, some of the destruction I observed afterwards even on Miami Beach--which was not as close to the eye as other areas--vied with the photos of damages from the great Miami Cat.4 of 1926.
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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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