Sea level rise: what has happened so far

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

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.

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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1782. Patrap
Atlantic,near Africa WV,LARGE IMAGE

Same View,Low Cloud Product
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1781. Patrap

GOES-12 Atlantic Basin WV Loop,wide view
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1780. Patrap
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Good Morning All.

A fitting tune for our Caribbean science project.
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shear dropping in the tropical alt g/mex and thr
e caribbean
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Good Morning;

Western-Central Caribbean soaked by upper level systems

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Good Morning Folks....Nothing shaking in the tropical Atlantic due to unfavorable shear conditions this am (as would normally be expected in June) but a few areas look interesting in the E-Pac.....With the usual "inverse" relationship between E-Pac vs. Atlantic activity, things could remain quiet on the Atlantic until things quiet down a bit in the E-Pac....Gotta wait for the MJO to slide over to the Atlantic I suppose and for sheer to drop...It has been dropping a little bit in the Western Caribbean over last few days so I suppose we will be watching the long-range models for hints of possible development over the next two weeks.........Have a great weekend and Dr. M should be posting his 2nd half of June outlook later today...I would suspect that he will probably come in around a 30% chance of a storm on the Atlantic side during the end of June...
Member Since: August 8, 2006 Posts: 0 Comments: 13949
the g/mex, caribean and the atlantic are very quiet this morning. in the caribbean abundant cloudiness abound ,as a result of an upper level trough. pressures are still low in the southwestern caibbean ,but vertical wind shear continues to be hostile and will preclude any tropical development for the next few days. looking at the shear tendecy maps this morning, indications are that shear is relaxing in most of the MDR and conditions for cyclogeesis will become favourable the next few days. the tropical wave east of the windward islands has lost some of it's convection and will only bring showers and occaisional thunder showers to these islands late tonight into tomorrow sat
the g/mex is devoid of any significant convection
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When ocean temperature is mentioned as relevant to the rise in ocean level, is this because of the expansion of the warmer water? Is there a coefficient associated with this?
Thank you.
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1771. viman
Good Morning everyone -- Hmmm
Lets break into song -- All the blobs are gone and the skiy is grey......
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Quoting TampaFLUSA:
....I read somewhere that they are planting a hardy orange tree in SE Georgia for cultivation...
Satsuma - a form of tangerine, grows in South Georgia and North Florida. It's quite tasty, but not very pretty visually. Best found at farmers markets and private fruit stands.

Haven't seen anything on big commercial plantings. But, then I don't read the newspapers much. And farmers being an independent sort of businessman wouldn't be likely to put out a press release.
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Morning all ^_^ troll's gone and replaced with empty space ^_^ also now that we're in the digital age I just realized that my laptop's video card will work :) but not the old style handheld tv I have :(

Just letting everyone in the US on this site know since anyone with a handheld analog TV in their hurricane supply list might not want to be stuck without any news
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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

Evening all. Not all people think that way unfortunately. :( I'm going to try to keep this short. Hubby told me not to go on a rant. Lol. I guess it would depend on your neighbors. The two big ones we've had recently, I could write a story and title it " A Tale of Two Storms" or "A Tale of two neighborhoods" After Rita we had the kind of neighbors one might want to use a fire arm against. But as much as that sucked, and boy did it ever, oddly it turned out for the best. Because for the frst time ever we do live in a neighborhood where everyone would do anything for the other. We've helped each other through 2 hurricanes. Everyone doing what we can. Its great! But yes, disasters do bring out the worst in some people. Never doubt that. I guess the best you can do is concentrate on the positives. Ok, I'm done now. Lol.
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night all including you to troll
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your the troll wack yourself
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later all see ya tommorow have a good night
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Quoting StSimonsIslandGAGuy:
Here is the palm that grows in Vancouver and Scotland and the Faeroe Islands. It also grows in Norway and the Alaska banana belt around Anette, AK:

....I read somewhere that they are planting a hardy orange tree in SE Georgia for cultivation...
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K, I am out of here... I have to work Friday :(
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Oh great troll season has started -_- or rather I should say its in about full swing -_-
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Quoting StSimonsIslandGAGuy:
Here is the palm that grows in Vancouver and Scotland and the Faeroe Islands. It also grows in Norway and the Alaska banana belt around Anette, AK:


Thats what we have.. good guess :)
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Quoting Vortex95:
1744. Thats nuts Orca it rarely gets over 95 here. Then again it rarely gets under 40 either. I love S Fla :).

This year:

Maximum Temperature
+40.2 °C at 16:31 on 03 June

Minimum Temperature
-5.1 °C at 02:47 on 10 March
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Quoting StSimonsIslandGAGuy:
We live with no cities with a population of over 20,000 within 80 miles / 130 kilometers.
20,000 toronto had 5 million as of 2000 9 years ago so i figure we are now at 6 i would guess if not more
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Quoting Orcasystems:

ROFLMAO, we have one on the deck by the pond. The climate in Victoria has to be seen to be believed... its was 104 here a couple weeks ago.

I really want to visit your island when I get my act together...from the photos it looks awesome...
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Quoting TampaFLUSA:

I was surprised to find out palm trees grow there....

ROFLMAO, we have one on the deck by the pond. The climate in Victoria has to be seen to be believed... its was 104 here a couple weeks ago.
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Quoting StSimonsIslandGAGuy:
Those are a kind of palm tree that grows in mountainous regions of southeastern China. They've been planted further north than that, in the Scottish Hebridies, and the Faeroe Islands.
Windmills I think they are called...I have seen them up to Virginia...
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1694. slickasatick

yeah, gonna have to hide this moron as i can barely take the pro-gorebull warming BS from Doc. Masters. i guess my piddly engineering degree cannot possible allow me to comprehend the supposed level of planetary destruction wrought by those evil CO2 emissions. the funny thing is that if the gracious Doc decided to fairly present both sides of the argument, I think I could more easily handle the bias...I realize this is TOO much to ask.
Member Since: September 14, 2007 Posts: 3 Comments: 3963
iam a paid member as well so it don't matter to me really
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your about to be replaced with empty space just like whats in your head

are you out yet must be time to go get another 20 piece on the corner
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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.
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