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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New Blog.
Member Since: Posts: Comments:
Quoting ClearwaterSteve:
Hey Kman and Drak How goes with you two.


Good evening to you. We are just taking a look at new data to see what's brewing in the Sw Caribbean. All is well.
Member Since: Posts: Comments:
Quoting Drakoen:
It looks more like a sharp inverted trough with broad low level turning than a closed low; the hi-res confirms such a philosophy.


Hard to tell but if you stitch together two sections of the Hi Res to cover the entire area there appear to be winds from all quadrants.
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Quoting Tazmanian:



so oh is takeing overe the blog the next 2 weeks????


I asked him on the blog earlier, but he did not answer so far. I am sure he will say on Friday or Saturday.
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Quoting ClearwaterSteve:
Hey Kman and Drak How goes with you two.


Pretty good gearing up for the season. You?
Member Since: October 28, 2006 Posts: 57 Comments: 30833
Hey Kman and Drak How goes with you two.
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Wow, you all were right on the severe weather item. Be careful out there.

img src="" alt="" />
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000
AXPZ20 KNHC 102148
TWDEP

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED JUN 10 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM
THE EQUATOR TO 32N...EAST OF 140W.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2115 UTC.

...SPECIAL FEATURE...
A LOW PRESSURE SYSTEM CENTERED NEAR 11N117W HAS BECOME A LITTLE
BETTER ORGANIZED THROUGHOUT THE DAY. SATELLITE IMAGES SHOW
IMPROVED CURVED BANDING TO THE N AND W OF THE ESTIMATED
LOW-LEVEL CENTER AND CONVECTION HAS DEEPENED AND IS MORE
CONCENTRATED NEAR THE CENTER...WITHIN 210 NM N AND 45 NM S
SEMICIRCLES. THE SYSTEM IS ALSO MORE DETACHED FROM THE ITCZ
BASED ON ITS OVERALL CLOUD STRUCTURE. RECENT SCATTEROMETER
PASSES REVEAL SW 20 KT WINDS OR SO OVER THE SE QUADRANT AND
ENHANCED NE TRADES OVER THE N SEMICIRCLE. THERE IS A MEDIUM
CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.

Member Since: Posts: Comments:
.
Member Since: October 28, 2006 Posts: 57 Comments: 30833
It looks more like a sharp inverted trough with broad low level turning than a closed low; the hi-res confirms such a philosophy.
Member Since: October 28, 2006 Posts: 57 Comments: 30833
567. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting sporteguy03:
Taz,
Quoting sporteguy03:
Dr.Masters,
Do you have any big vacations coming up? Then the tropics will heat up!





so oh is takeing overe the blog the next 2 weeks????
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The low depicted on this graphic needs relocating about 5 degrees further East.

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Quoting IKE:


And it begins....93L is next.

Ike,
Probably on Sunday since Dr.Masters will be on a plane to Europe then :)
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Quoting Vortex95:
557. ARE YOU SURE CCHS are you fully awake? jk :)


Nope. Just sleep-typing and sleep-forecasting right now I guess! lol
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561. IKE
Quoting kmanislander:
Well, no doubt that there is a low in the SW Caribbean.

This evening's Quikscat pass


And it begins....93L is next.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Taz,
Quoting sporteguy03:
Dr.Masters,
Do you have any big vacations coming up? Then the tropics will heat up!


Quoting JeffMasters:


Yes, I am leaving Sunday for my first-ever European vacation, a 2-week trip to London and Kefallonia Island, Greece. I trust there will be plenty of tropical action to follow during the time I'm gone! I'll post an last half-of-June outlook on Friday or Saturday before I go.

Jeff Masters
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Quoting kmanislander:
Well, no doubt that there is a low in the SW Caribbean.

This evening's Quikscat pass


Seems like the evolution may be beginning. Will just have to wait and see whether this holds and becomes better defined and to see whether this will be the focus for what the computer models have been suggesting.
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It would appear that the blow up we are seeing just SE of Jamaica is coming off of the Northern edge of that low. You can see the contaminated wind barbs in black where the thunderstorms are.

Were it not for shear that convection would likely wrap into the low in short order and spell trouble
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Quoting Vortex95:
I think I shall make a law similar to Gowdin's law.

Vortex's law: As a Wunderblog discussion grows longer, the probability of a comparison involving Hurricane Andrew or Hurricane Katrina approaches 1.


Obviously, that is like a blog about war and conflict not discussing World War 1 and World War 2
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Well, no doubt that there is a low in the SW Caribbean.

This evening's Quikscat pass
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Quoting presslord:
I am really proud of our cleaning/rebuilding project this weekend in Volusia County...

while disasters such as localized wildfires and flooding don't have the media-wide sex appeal as a huge hurricane, they are still devastating to their victims...and afford us perfect opportunities to fulfill our mission:

Meeting the needs of un-served, under served and forgotten people...

...so...

Many thanks to everyone who is making this possible - from financial contributors to those who remember us in their thoughts and prayers to those who are going to be onsite working...

My view is that we are creating a movement here...and it's pretty cool to be a part of it...

www.portlight.org


Prolific and very well said. Thank you sir for your fine work.
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Quoting Acemmett90:
Weather Predicting is a theroy not fact so stop argueing



do i smell JFV # 2???
Member Since: Posts: Comments:
I am really proud of our cleaning/rebuilding project this weekend in Volusia County...

while disasters such as localized wildfires and flooding don't have the media-wide sex appeal as a huge hurricane, they are still devastating to their victims...and afford us perfect opportunities to fulfill our mission:

Meeting the needs of un-served, under served and forgotten people...

...so...

Many thanks to everyone who is making this possible - from financial contributors to those who remember us in their thoughts and prayers to those who are going to be onsite working...

My view is that we are creating a movement here...and it's pretty cool to be a part of it...

www.portlight.org
Member Since: Posts: Comments:
Quoting cchsweatherman:


Just learning from the mistakes that I've made in doing my analysis and making observations the past couple days. Think, at least for me, it'd be easier to take a wait-and-see approach.


Of course its always good to be cautious, but this time it might be a reality.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Man have we had a rough night here in the Dallas area. Had a weak tornado touch down only a couple of miles from me...I'm in Plano. We've had some damage all over...wind gusts around 80-85mph in many places.
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Quoting extreme236:


Well when I see the HPC begin mentioning cyclogenesis in their outlooks I tend to pay close attention. We do have a precursor disturbance east of Jamaica now...probably what will be the eventual low pressure system.


Just learning from the mistakes that I've made in doing my analysis and making observations the past couple days. Think, at least for me, it'd be easier to take a wait-and-see approach.
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546. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37860
It looks like something that will take a while to coalesce; nevertheless, these system can become significant once they form. A track into the western GOM would be unfavorable for the maintenance of a tropical cyclone.
Member Since: October 28, 2006 Posts: 57 Comments: 30833
Quoting kmanislander:
Neutral = more active season

El Nino = less active

Of course, that only refers to numbers of storms, not intensity of the one that may come ashore in a major coastal metropolis.


Given the right time and the right conditions, a tropical cyclone will form regardless of the teleconnections. If a storm is there when conditions are favorable, cyclogenesis will occur which is what happened in 2004.
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Quoting kmanislander:
Neutral = more active season

El Nino = less active

Of course, that only refers to numbers of storms, not intensity of the one that may come ashore in a major coastal metropolis.


See my avatar for my reference.
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Do you think the models are feeling the effects of El Niño ?

They seem a bit fickly :)


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Computer models tend to do better in the heart of the season. They struggle some in the early and late stages.
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Quoting cchsweatherman:


Would seem that way with the computer models, but I think that I'll wait to see something evolve before buying into them. Doing this since the computer models have continued to suggest that 3 to 5 days out conditions would be favorable for cyclogenesis, but then when it comes 3 to 5 days time, there's absolutely nothing and the conditions didn't become favorable. Yes I recognize that early on I did consider the computer models when making my analysis, but I've become more and more skeptical as nothing the computer models have shown has come to fruition.


Well when I see the HPC begin mentioning cyclogenesis in their outlooks I tend to pay close attention. We do have a precursor disturbance east of Jamaica now...probably what will be the eventual low pressure system.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Drakoen:
I see that all of the computer forecast models with the exception of the UKMET forecast for development. Conditions for cyclogenesis will be favorable 3-4 days from now.


Would seem that way with the computer models, but I think that I'll wait to see something evolve before buying into them. Doing this since the computer models have continued to suggest that 3 to 5 days out conditions would be favorable for cyclogenesis, but then when it comes 3 to 5 days time, there's absolutely nothing and the conditions didn't become favorable. Yes I recognize that early on I did consider the computer models when making my analysis, but I've become more and more skeptical as nothing the computer models have shown has come to fruition.
Member Since: Posts: Comments:
Neutral = more active season

El Nino = less active

Of course, that only refers to numbers of storms, not intensity of the one that may come ashore in a major coastal metropolis.
Member Since: Posts: Comments:
Quoting kmanislander:
529. extreme236 1:23 AM GMT on June 11, 2009

There is some suggestion of a progression back to neutral. Yet one more "wait and see " issue this year.


Hmm...interesting.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
536. TX2FL
Quoting kmanislander:
529. extreme236 1:23 AM GMT on June 11, 2009

There is some suggestion of a progression back to neutral. Yet one more "wait and see " issue this year.


That could make things even more interesting. One would thing that the borderline neutrality/El Nino will substantiate the theories of storms blowing up closer to land.
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Quoting Drakoen:
I see that all of the computer forecast models with the exception of the UKMET forecast for development. Conditions for cyclogenesis will be favorable 3-4 days from now.


We have a 3 day weekend coming up so please reprogramme those computers for next week !
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529. extreme236 1:23 AM GMT on June 11, 2009

There is some suggestion of a progression back to neutral. Yet one more "wait and see " issue this year.
Member Since: Posts: Comments:
I see that all of the computer forecast models with the exception of the UKMET forecast for development. Conditions for cyclogenesis will be favorable 3-4 days from now.
Member Since: October 28, 2006 Posts: 57 Comments: 30833

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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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