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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Goodmorning all
Havent said much latley, not much to say about the tropics now anyway. Finished all my house mods to hopefully make ti a litttle more wind resistent. (accordint to the county anyway) Ran the generator last night. Hope not to need it this season but who knows?
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look forward to it dbw

morning michfan, good to see ya again
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Good morning everyone.
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see you here, sj
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On the way to Volusia County
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Good Morning;

Heavy Showers Continue Over Western-Central Caribbean
Member Since: July 24, 2005 Posts: 407 Comments: 19076
morning
wind shear in the g/mex ,cvarib and the atl continues o to be very hostile, precluding the possibility of any tropical development in the near future. the surface low that was in the southwest caribbean near panama has weakened and will continue to do so maybe to a surface trough.latest water vapour imagery shows a mass of convection heading east towards the lesser antilles. it appears this an upper level trough which is advecting high and medium clouds towards the islands. it appears he islands will have wet and blustery conditions with the interaction of the system moving east and the moderately strong tropical wave approaching the area although conditions are not favourable for tropical development, the area is only a matter of interest
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Link

Typhoons can trigger imperceptible, slow earthquakes, researchers say.

Scientists report in the journal Nature that, in a seismically active zone in Taiwan, pressure changes caused by typhoons "unclamp" the fault.

This gentle release causes an earthquake that dissipates its energy over several hours rather than few potentially devastating seconds.

The researchers believe this could explain why there are relatively few large earthquakes in this region....
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Morning all

Quoting homelesswanderer:
Before my computer froze the model it looked like 00z GFS takes it east and out to sea. I think.


The "freezing" could be a Java memory problem. Check here for a possible fix.

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Thanks Gator. Those are great links. Was wondering how everyone could see whats happening in the Caribbean because the link I had just covered the gulf.
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http://moe.met.fsu.edu/tcgengifs/, or here, but shorter loops, not that going 16 days out is really all that useful, but curiosity usually wins the battle.
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http://tc.met.psu.edu/, this is the page I usually use
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Quoting GatorWX:


ngp and cmc bring it west, doesn't look like gfs develops it at all, but does look like it bring most of the energy north and then ne.


yeah. I was wondering what happened on the gfs. It appears they think there will be a weakness in the ridge. And whatevers left of it will go out to sea? Complete 180 for them. I was trying to see this link to gfs but it kept freezing. Don't know if you have this on your new computer.

Link
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Quoting homelesswanderer:
Before my computer froze the model it looked like 00z GFS takes it east and out to sea. I think.


ngp and cmc bring it west, doesn't look like gfs develops it at all, but does look like it bring most of the energy north and then ne.
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Nevermind, I found it, thanks though
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Levi, I have a new computer I'm working with, do you have a link to the experimental models page? if so I'll google it. Thanks
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yea, just about shot now, looks good, cloud tops have warmed slightly, but with the new band forming, warming trend shouldn't persist too long once established. I would imagine this is also evidence of a new surface feature as well.
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Before my computer froze the model it looked like 00z GFS takes it east and out to sea. I think.
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Quoting GatorWX:
Sorry Levi, didn't read your entire statement, you basically stated the same thing. And I just looked again at the visible, and only th one llc is evident. But as you and I stated, it certainly appears a new one will form or has already under the main mass of convection.


I keep doing that today lol.

Yeah it would be nice to have some fish storm to track at least.
Member Since: November 24, 2005 Posts: 635 Comments: 26553
Sorry Levi, didn't read your entire statement, you basically stated the same thing. And I just looked again at the visible, and only th one llc is evident. But as you and I stated, it certainly appears a new one will form or has already under the main mass of convection.
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it looked to me like two circulations, if there are both a mid level and a displaced low level circulation, I would imagine a new surface low will form under the convection. The present surface low seems to be weakening quite quickly. I looked earlier as well when the sun was still up and noticed the second, but it appeared to me the main circultation was at the low levels too. Actually appeared to be a third low level swirl as well to the immediate south of the convection.
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Quoting GatorWX:


Very surprised 91E was not declared a depression at 11PM or 2AM. Certainly in the morning it will. Cloud tops staying quite cool over center, convection is certainly persistent, outflow has increased. New main feeder band is forming to the north giving the storm a classic developing cyclone appearance. Would not be at all surprised to see a healthy TS out of this in 48 hrs if conditions hold up (right now, haven't looked at anything but sat loops.) Certainly his is the most impressive feature in the tropics.Our Atlantic low doesn't really appear to even be trying under all that vertical shear, and other than it,nothing else to even speak of. Shear looks pretty prohibitive over the entire basin for at least the next week and a half. Have fun yall!


91E wasn't classified because the main surface circulation is displaced to the SW. The blob that looks impressive is actually the mid-level circulation, but it is becoming dominant and forming a new LLC under it, so by tomorrow it may have a shot at becoming a TD.
Member Since: November 24, 2005 Posts: 635 Comments: 26553
Quoting winter123:
Not much tropics to talk about, but if you're interested here's tonights post. Night :)
http://www.wunderground.com/blog/winter123/show.html


Very surprised 91E was not declared a depression at 11PM or 2AM. Certainly in the morning it will. Cloud tops staying quite cool over center, convection is certainly persistent, outflow has increased. New main feeder band is forming to the north giving the storm a classic developing cyclone appearance. Would not be at all surprised to see a healthy TS out of this in 48 hrs if conditions hold up (right now, haven't looked at anything but sat loops.) Certainly his is the most impressive feature in the tropics.Our Atlantic low doesn't really appear to even be trying under all that vertical shear, and other than it,nothing else to even speak of. Shear looks pretty prohibitive over the entire basin for at least the next week and a half. Have fun yall!
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Quoting 7544:
hmm our carb blob is looking better at this hour but does anyone think it might get that far west with the high building in the gom and would be further to the east


The low will most likely drift NW into the NW Caribbean and then turn towards the west under the influence of the blocking high over the northern Gulf of Mexico. If the system remains weak I don't see it affecting anybody north of 27N.
Member Since: November 24, 2005 Posts: 635 Comments: 26553
708. 7544
hmm our carb blob is looking better at this hour but does anyone think it might get that far west with the high building in the gom and would be further to the east
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Not much tropics to talk about, but if you're interested here's tonights post. Night :)
http://www.wunderground.com/blog/winter123/show.html
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Just a call from somebody talking about they are doing something in the Carribbean this weekend. The lady name was Ana and she said that she is in the Carribbean right now organizing to have a blast!
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May 26th SST's


June 7th SST's
Member Since: September 2, 2007 Posts: 178 Comments: 20439
704. Skyepony (Mod)
Buoy 42058 is under there. Near 20kts & 8ft seas. Some ships left the area.
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703. JRRP

50kts
see you later...
Member Since: August 16, 2007 Posts: 0 Comments: 5458
That's my bet the ull will combine with the low in the Caribbean if that is possible. Right around Jamacia.
Member Since: August 18, 2008 Posts: 0 Comments: 3112
701. JRRP
Quoting Tazmanian:
poor me no one cares about my posts

lol
i see u
Member Since: August 16, 2007 Posts: 0 Comments: 5458
700. Skyepony (Mod)
Have to see if it keeps its proper distance or shreads it.
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699. Skyepony (Mod)

indeed~ It seems to be moving to that angle that shields & feeds a blob.
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According to the Quicksat there is a Surface Circulation South of the Disturbance.
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Quoting Skyepony:
Interesting the ULL over the Bahamas rushing toward the flare up in the Caribbean.


That is whats causing the flare up!
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696. Skyepony (Mod)
Interesting the ULL over the Bahamas rushing toward the flare up in the Caribbean.
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poor me no one cares about my posts
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Unexpectedly, the upper trough is lifting east and north and the latest satellite imagery supports this with diffluent zone shifting further east and north near Hispaniola.

Night all

Member Since: July 24, 2005 Posts: 407 Comments: 19076
you can see that gap going bye bye vary well in this loop


Link
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692. Skyepony (Mod)
Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, Florida, USA

The potential effects of Greenland Ice Sheet (GrIS) melting on the Atlantic meridional overturning circulation (MOC) and global climate in the 21st century are assessed using the Community Climate System Model version 3 with prescribed rates of GrIS melting. Only when GrIS melting flux is strong enough to be able to produce net freshwater gain in upper subpolar North Atlantic does the MOC weaken further in the 21st century. Otherwise this additional melting flux does not alter the MOC much relative to the simulation without this added flux. The weakened MOC doesn't make the late 21st century global climate cooler than the late 20th century, but does reduce the magnitude of the warming in the northern high latitudes by a few degrees. Moreover, the additional dynamic sea level rise due to this weakened MOC could potentially aggravate the sea level problem near the northeast North America coast.

Received 3 March 2009; accepted 6 May 2009; published 29 May 2009.

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Quoting Vortex95:
687. it is vestiges of my dad that I have been tying to get rid of for years, sometimse they get out. He is very grumpy, he even is grumpy about the fact that he is grumpy signifiying his grumpiness.


I think my daughter and son would agree with you on that (about me).. roflmao, maybe even my grandson.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
do you we call that tampespin was saying the water was cooling and the cooler water where moveing W or N well that gap that was opening and moveing W or N is gone now looks like El nino is well under way


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Quoting Vortex95:
I don't know what to think of orca anymore he thinks mindwise i'm an 80 year old insane assuylum escapey. Ah well :)


ROFLMAO... no.. but at times you do act like a grumpy old man.. I know..I am one :)

and NO, you can't post the picture again :)

Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting Orcasystems:


Never wrong... and seldom wrong
Different meanings


Keep that halo tight on your head before a freudian slip gets you in trouble. LOL!
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Quoting Drakoen:


Never being wrong is a problem in itself lol


Never wrong... and seldom wrong
Different meanings
Member Since: October 1, 2007 Posts: 81 Comments: 26511

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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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