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 StSimonsIslandGAGuy:
I've often thought that blogging should be reserved for the paid members, would make things much more serious.


I think that would take the fun out of it :)
I am a member and so is SWMBO, but thats just to support the site... if I HAD to be a paid member, I probably would not.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting Orcasystems:


No, and around here they are all sort of individual areas. Victoria proper is actually quite small.. the small surrounding bedroom communities (Langford,Colwood, Highlands) are individual geographical areas in their own right...

I was surprised to find out palm trees grow there....
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Quoting TampaSpin:


wasnt that what i said, you could do it manually? Does that make it auto then?


You can actually set the time in the command or put it into a .bat file. I believe the standard is three days.

Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting Vortex95:


would you consider suburban areas to be part of cities?


No, and around here they are all sort of individual areas. Victoria proper is actually quite small.. the small surrounding bedroom communities (Langford,Colwood, Highlands) are individual geographical areas in their own right...
Member Since: October 1, 2007 Posts: 81 Comments: 26493
1723. KEEPEROFTHEGATE (Mod)
i have a degree in troll removal
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1722. KEEPEROFTHEGATE (Mod)
Quoting Orcasystems:
When it is all said and done... I do own weapons, and would not have a second thought about using them. I would just be absolutely shocked if it happened.
thats like myself orca my first response would be to help first clean up get everything back to normal if a diaster stuck i think most people would i hope
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Quoting Orcasystems:


Just do this:

ipconfig /release
ipconfig /renew



wasnt that what i said, you could do it manually? Does that make it auto then?
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There should be a waiting period for membership for at least 24 hours bf they send your confirm code...
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Quoting TampaSpin:


NOpe you can reset it everytime you log on but not automatically i don't think.....YOu can do a manual reset tho.


Just do this:

ipconfig /release
ipconfig /renew

Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting StSimonsIslandGAGuy:
Doesn't your IP change every time you turn on your computer?


It can.....
The only way to semi track it is to track the MAC address... but that can be spoofed also.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting StSimonsIslandGAGuy:
Doesn't your IP change every time you turn on your computer?


NOpe you can reset it everytime you log on but not automatically i don't think.....YOu can do a manual reset tho.
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Quoting StSimonsIslandGAGuy:
Doesn't your IP change every time you turn on your computer?

Most change once a month on average...like our cable co here in Fl, dunno about the rest...
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Quoting Vortex95:
orca you have mail and thanks for answering. In the U.S. if you were to go 1000 houses at 2 p.m. and all said houses had people in them 999 out of a 1000 would have their front door locked generally, some areas of course may be more lax.


I know the big citys are probably like that... heck in our little Strata area... not only would they not be locked.. but if someone came over.. they would just give a quick knock on the door...and walk in.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
1705. KEEPEROFTHEGATE (Mod)
StSimonsIslandGAGuy still clean just getting over run by the out of control gun carring punks and we can not seem to stop it its just getting worse and worse everyday when i first moved to toronto it was so nice here you could sleep with your doors unlocked shootings and such were unheard of but times are changing and fast
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Is there a way they can see if the same person is posting under the same IP address and ban that IP?
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Quoting StSimonsIslandGAGuy:
Toronto seemed fantastically clean when we've visited there. But still very American. We like the 'real' Canada in Quebec province.


Oh that was bad.. really bad... now I know why I have a gun :)
Member Since: October 1, 2007 Posts: 81 Comments: 26493
When it is all said and done... I do own weapons, and would not have a second thought about using them. I would just be absolutely shocked if it happened.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
Y'all do us all a favor and hit the "-" on youknowwhat.
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Quoting tennisgirl08:
Just stepped in. Can anyone update me on the Caribbean disturbance? Any chance for development? If so, when? Thanks


NO i don't think so.....if so your looking 5-7 days out before anything gets going.
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Quoting KEEPEROFTHEGATE:
i don't know anymore orca the past couple of years been gettin rough here in the city just yesterday a group of 3 mugged an 80 year old woman behind my building they used such force they broke her hip spineless cowards there has been at least three or four gunplay incidents and sept of last year one of my tentants got shot in the back lost a kidney only 18 most of it is gang related i guess

so the anwser is at the moment it may not be a bad idea to have something just in case


Vancouver is pretty bad now a days also.. thats the nice thing about the Island.. no real gangs. Even the Hells Angels have a vacation spot up Island, and never come close to causing problems.

I guess its because of Victoria... very laid back... and you know there is going to be at least one active or retired Military guy in every neighbourhood. Heck, we are even used as a International example and training program for Neighbourhood watch (Sydney Australia Police were here for two weeks to copy the system)
Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting Orcasystems:


I didn't say it was ignorant?
I just don't understand it? I would bet that of the 29 houses in our Strata area.. maybe 5 of us have weapons.. and all 5 are ex/active military or RCMP.

The thought that I would have to defend myself, my family or my neighbours in the event of a natural disaster is just ludicrous up here. I am going to have to say its a completely different social mentality in Canada.

That being said.. KOG is in or close to Toronto.. again a different mentality over there also.


Providence, RI had all the same riots, rapes, robberies, etc. after the 1938 hurricane. A real mini NOLA-immediately-after-Katrina in the now-liberal New England, imagine that.

Under the right circumstances the not-so-right folks among us that are coherent enough to recognize that any police force is well stretched and communication is impossible may come out to play in what ever way they see fit.

Trusting that all of my neighbors are not of this affliction, that the police could respond quickly, and that I could successfully contact them is asking a lot. Not even after little old Gustav, 60 miles NE from the landfall point, could I have called the police if I wanted to for a good 36 hours afterward.
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1688. KEEPEROFTHEGATE (Mod)
as for locks on my doors i have standard lock with two slide bolts on front door back door has standard lock with dead bolt at top sliding bar in middle also have adt alarm on doors and windows as well monitored 24 7 365
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alright, i have to go to work in the morning...see you then!
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1683. Orcasystems

I truly long for the day when it is the same in Texas...however, I will NEVER trade my right to bear arms for supposed government-guaranteed security.
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Quoting Vortex95:


I have noted this much more turstworthy society in Canada i'm not sure why but here people are just far less trusting, i.e. media in the U.S. is negatively charged (love talking about crime and tragedy especially local news), amoungst other complex societal issues. Btw Orca just Curious do you lock your front door?


Standard door lock.. no extra dead locks.. no locking bars. Standard sliding door lock for the back.. nothing fancy.

Front door is locked when we are not home.. or asleep... the rest of the time it is not.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
1682. KEEPEROFTHEGATE (Mod)
i don't know anymore orca the past couple of years been gettin rough here in the city just yesterday a group of 3 mugged an 80 year old woman behind my building they used such force they broke her hip spineless cowards there has been at least three or four gunplay incidents and sept of last year one of my tentants got shot in the back lost a kidney only 18 most of it is gang related i guess

so the anwser is at the moment it may not be a bad idea to have something just in case
Member Since: Posts: Comments:

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About

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