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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Quoting canesrule1:
yea
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Quoting hurricane23:
epac disturbance poofed.
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1279. Michfan
Quoting RitaEvac:


Shear can drop on the dime, shear cant be predicted accurately at all.


Depends on how long you define a dime to be.
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Quoting AstroHurricane001:
Just in case you haven't heard yet, the H1N1 flu outbreak is now at full pandemic level, the first time this was issued in 41 years. Seasonal flu is also down, so if there's a flu going around at your place of work/school it could indeed be swine flu.
damn your right i forgot about that swine flu thing, scary.
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i predict cat 5 at 11pm
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epac disturbance poofed.
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Quoting IKE:


I changed it to a link. Gross.
i know its worse than a mummified mummy.
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Ike - Spector is a scary guy. A general question for anyone who knows - Why did Jim Cantore start doing the morning weathercast? Saw him the first day when he got irritated at being identified as "new to the show." Just wondered.
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Quoting extreme236:


98.9%? Hard to get more random than that
no, maybe 14.9 or 58.2 or maybe even 38.6 is more random???lol
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1272. IKE
Quoting gordydunnot:
Ike he looks like your run of mill murderer.


I changed it to a link. Gross.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Just in case you haven't heard yet, the H1N1 flu outbreak is now at full pandemic level, the first time this was issued in 41 years. Seasonal flu is also down, so if there's a flu going around at your place of work/school it could indeed be swine flu.
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Quoting TheCaneWhisperer:


Surely before November, 100% chance.


mid to late august to early september is not out of the question.
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1268. Levi32
Quoting WeatherStudent:


So it will not be a SF threater anymore, Levi?


SF threater? Sorry what is that lol?
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Quoting canesrule1:
i wouldnt say 100% its an El Niño year so ill bring that 100% down to i dont know 98.9% or something around that.


98.9%? Hard to get more random than that
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Quoting WeatherStudent:


So it will not be a SF threater anymore, Levi?
i think it still is, my friend, keep you eyes peeled.
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Quoting TheCaneWhisperer:


Surely before November, 100% chance.
i wouldnt say 100% its an El Niño year so ill bring that 100% down to i dont know 98.9% or something around that.
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Ike he looks like your run of mill murderer.
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HOG glad to know you are around even under a new name.
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How long will this Caribbean blog be there?
anyway the 91E has been upped to 50+%
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There isnt much going on in the tropics.

TW passing 53W is a moisture surge along the ITCZ and will weaken as it goes into S America on Friday.

TUTT sharpens the NW carribean with a upper low over the s-central bahamas. Shear in excess of 30kts dominate the region with alot of dry air in the NW carribean. A surface trough (Not Low) is just east of the TUTT. Until the TUTT weakens and the upper low moves out or weakens.. this area will not be favorible for tropical development.
The enviroment might be better in 2-3days near Cuba but with all the dry air and high pressure in the GOM.. right now, chances are under 30% for development.

I still say wait till mid-late next week near the bahamas! been pushing this for a couple days now.
Member Since: January 22, 2006 Posts: 0 Comments: 1689
Quoting canesrule1:
Development imminent? thoughts...


Surely before November, 100% chance.
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Quoting beell:


Heck, even I feel smarter!
Thanks


I may not have stated it properly, the visiting mets along with the instructor write the International Tropical Discussion.
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1256. Levi32
The environment in the Caribbean will become favorable in 3-4 days, but not extremely so. I don't see the conditions necessary to turn a broad low born from a land-thermal low into a tightly-wound TS within the time that it will have in the Caribbean. However it does need to be watched and depending on how it looks in 5 days it may try to develop in the Gulf of Mexico when the ridge tries to build over top.
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1255. hydrus
Quoting canesrule1:
forget it, i did it.
lol...
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1254. beell
Quoting nrtiwlnvragn:


Ya, they do a good job. It's actually training for visiting mets from the Carribean and South America.


Heck, even I feel smarter!
Thanks
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Quoting eye2theskies:


That was disturbing...
i know it looks like a Halloween costume gone bad.
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forget it, i did it.
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Quoting IKE:
Phil Spector without his wig, in a mugshot....




Now, back to the weather.


That was disturbing...
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I took a picture of my new car and now i dont know who to put it as the little image next to my handle, can someone please help, thanks.
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Development imminent? thoughts...
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My opinion is that significant development is not likely in the next 48 hours until the shear drops to more reasonable levels. For now all we have is a blob with something on the surface and a few models.
But thats how they all start. So I agree for the most part with Adrian.
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That Tsunami statement was issued on 6/1. I wonder if one will be issued for today's event. The last one that the statement was in response to didn't trigger the buoy.
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Quoting WeatherStudent:


Really Adrian? Despite conditions expected to become tremendously favorable in the Carib between 24-48-72 hours from now? Moreover, I'll take your feedback into consideration, since afterall, you do have a B.A. Degree in tropical meteorology, so that would lead me to believe that you must know a thing or two in regards to the tropics.


All i see are fast upper level winds racing through the caribbean which for the time being will impede development atleast in the near term.If you like tracking cyclones the news for this season just is not encouraging as the TNA came in ealier today at 0.41C. If youre wondering what the TNA is well is an index the climate prediction center uses to measure sst's across parts of the atl.I would venture to say 9-12 named storms seems like a good bet.A friend did a blog today concerning the TNA.

As in any year the caribbean is a hot spot this time of the year so its any area to keep an eye on.
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1245. IKE
Phil Spector without his wig, in a mugshot....

Link


Now, back to the weather.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting canesrule1:
what is HOG?


I believe that it is House of Gryfindor, which was his old handle.
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Quoting beell:


Thanks, nrt. Guess I should have read the discussion first!

A great discussion, btw.


Ya, they do a good job. It's actually training for visiting mets from the Carribean and South America.
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Quoting hurricanemaniac123:


CybrTeddy, what are your predictions on the two AOI? (The W. Carribean and the Atlantic ones)


As was stated the wind shear is pretty darn strong. But shear tendency's are already dropping.
There also appears to be something weather it be a MLC or a LLC in the area.
This was last nights descending pass.

This was this mornings ascending pass.

This is the 850 MB vort, something weak is at the surface it would appear, but its very broad and disorganized at best.

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what is HOG?
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1239. beell
Quoting nrtiwlnvragn:


Believe so...A TUTT OVER THE CENTRAL ATLANTIC LIES TO THE SOUTH/SOUTHWEST TO JUST NORTH OF THE GUIANAS.


Thanks, nrt. Guess I should have read the discussion first!

A great discussion, btw.
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Quoting RitaEvac:


Shear can drop on the dime, shear cant be predicted accurately at all.
for sure i agree 100%
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Quoting nrtiwlnvragn:


No, at least I didn't.


Well now you all know.
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To: Puerto Rico and Virgin Islands coastal regions
From: NOAA/NWS/West Coast and Alaska Tsunami Warning Center
Subject: Tsunami Information Statement issued 06/1/2009 at 12:37AM AST

At 12:34 AM Atlantic Standard Time on June 1, an earthquake with preliminary magnitude 4.5 occurred 170 miles/274 Km northeast of Christiansted, US Virgin Is..

The magnitude is such that a tsunami WILL NOT be generated. This will be the only WCATWC message issued for this event.

The location and magnitude are based on preliminary information. Further information will be issued by the United States Geological Survey or the appropriate regional seismic network.


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Quoting CaneWarning:


I thought everyone knew I was HOG.


No, at least I didn't.
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Quoting Michfan:
Until the shear drops it is all a guessing game.


Shear can drop on the dime, shear cant be predicted accurately at all.
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Quoting canesrule1:
really? i think AOI will become something (the one in caribbean) maybe a TD in the next 48 hours.


it could happen you never know
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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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