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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932. jeffs713
4:03 PM GMT on June 11, 2009
Quoting TampaSpin:


I always had the best...LUCK..LOL when systems are not fully developed into a Depression to use the 400mb steering without a true closed Low at the surface...Just what i have the best luck with ......could be wrong...

It actually makes sense, too. If you look at Nexrad radars here on WU when there are thunderstorms, the storms tend to move in the same direction as winds in the middle to upper layers (10-25k feet), which corresponds with the 400mb layer, IIRC. (use the vertical azimuth display to see winds at different levels)
Member Since: August 3, 2008 Posts: 16 Comments: 5882
930. beell
4:02 PM GMT on June 11, 2009
Ok, thanks-luck is certainly a factor in predicting weather.
Member Since: September 11, 2007 Posts: 143 Comments: 16649
929. TampaSpin
4:00 PM GMT on June 11, 2009
Quoting beell:
But i would use the 400mb Steering for a non developed blob of clouds

TS, why would you use an upper level steering chart for a low level blob?


I always had the best...LUCK..LOL when systems are not fully developed into a Depression to use the 400mb steering without a true closed Low at the surface...Just what i have the best luck with ......could be wrong...
Member Since: September 2, 2007 Posts: 178 Comments: 20439
928. futuremet
3:57 PM GMT on June 11, 2009
Member Since: July 19, 2008 Posts: 43 Comments: 4051
927. futuremet
3:56 PM GMT on June 11, 2009
Yes, the vorticity seems to be Coalescing

Quoting KEHCharleston:
Still learning so bear with me for a moment.

We have a blob currently at 9N 52W. It is an area of decreasing shear. It shows up nicely on the right bottom corner of the visible satellite (visible is best for seeing surface, right?). Is this associated with a wave? What steers it west?

At about 15N 75W, we have another blob.
It sits in an area which is under a generally lowering pressure (part of the trough?)


If these two features come together we have Ana?

Again... just learning, not disputing any ones opinion.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
925. Levi32
3:56 PM GMT on June 11, 2009
Good morning all.

Tropical Tidbit for June 11th

Mirror site with links and current info
Member Since: November 24, 2005 Posts: 635 Comments: 26647
924. TampaSpin
3:56 PM GMT on June 11, 2009
Quoting Vortex95:
916. That would definatly explain why it is stalled.


Yep its hemmed in and no place to go..but move North some....the High in the GOM should move East in time and allow for a more NW move in the Caribbean..
Member Since: September 2, 2007 Posts: 178 Comments: 20439
923. beell
3:55 PM GMT on June 11, 2009
But i would use the 400mb Steering for a non developed blob of clouds

TS, why would you use an upper level steering chart for a low level blob?
Member Since: September 11, 2007 Posts: 143 Comments: 16649
921. IKE
3:54 PM GMT on June 11, 2009
Quoting WeatherStudent:


Wouldn't that significantly prolonge the current wind shear outbreak in the Carib presently, Ikster?


Until it moves out.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
920. KEHCharleston
3:53 PM GMT on June 11, 2009
Thanks Tampa

Thanks WPBHurricane05
Member Since: August 19, 2008 Posts: 6 Comments: 2490
917. WPBHurricane05
3:51 PM GMT on June 11, 2009
Quoting KEHCharleston:
It shows up nicely on the right bottom corner of the visible satellite (visible is best for seeing surface, right?).


I like to use RGB, it shows surface circulations the best.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
916. TampaSpin
3:51 PM GMT on June 11, 2009
Quoting KEHCharleston:
Still learning so bear with me for a moment.

We have a blob currently at 9N 52W. It is an area of decreasing shear. It shows up nicely on the right bottom corner of the visible satellite (visible is best for seeing surface, right?). Is this associated with a wave? What steers it west?

At about 15N 75W, we have another blob. It sits in an area which is under a generally lowering pressure (trough)

If these two features come together we have Ana?

Again... just learning, not disputing any ones opinion.


You have layers of moving air currents that steer clouds.....700-850mb is used to steer a developed Tropical Storm or depression...things that get Stronger are then steered at higher levels.....

Here is the 700-850mb


But i would use the 400mb Steering for a non developed blob of clouds.

Member Since: September 2, 2007 Posts: 178 Comments: 20439
915. CycloneOz
3:46 PM GMT on June 11, 2009
Quoting TampaSpin:
871. Orcasystems 10:49 AM EDT on June 11, 2009
Quoting TampaSpin:
9N 52W will become the first Named Storm of the year....Good Morning everyone


You mean the little blob under 35 knots of shear?


Orca did i say it was going to develop in that location.....You Question everything i say on here even if i said i was going to the JOHN i would believe....People are really getting very tired of your attacking!



LOL! :D

Member Since: August 26, 2006 Posts: 10 Comments: 3684
914. OSUWXGUY
3:44 PM GMT on June 11, 2009
El Nino is coming despite some interesting SST loops appearing around here the past couple days...

First check out the T-Depth anomaly animation

CPC - Move Cursor to T-Depth

Also check page 16 of the weekly ENSO discussion - there was a Kelvin Wave crossing the Pacific in Mid April to Mid May that caused the recent warming, with a cool phase starting towards then end of May. The next Kelvin wave will take us back above the 0.5°C threshold for El Nino.

Weekly ENSO Discussion PDF
912. KEHCharleston
3:41 PM GMT on June 11, 2009
Still learning so bear with me for a moment.

We have a blob currently at 9N 52W. It is an area of decreasing shear. It shows up nicely on the right bottom corner of the visible satellite (visible is best for seeing surface, right?). Is this associated with a wave? What steers it west?

At about 15N 75W, we have another blob.
It sits in an area which is under a generally lowering pressure (part of the trough?)


If these two features come together we have Ana?

Again... just learning, not disputing any ones opinion.
Member Since: August 19, 2008 Posts: 6 Comments: 2490
911. charlottefl
3:36 PM GMT on June 11, 2009
They're warm enough for a storm moving along. A slow mover would likely cause upwelling underneath it.




HAHA! Great Minds Think Alike!
Member Since: December 18, 2006 Posts: 7 Comments: 2686
910. IKE
3:35 PM GMT on June 11, 2009
Quoting AllWeatherFriend:
How are the temperatures in the Gulf of Mexico at this time of the year? Are they warm enough for tropical storm development? I'm asking because the forecast for the next five days will be approaching the mid-90's and usually that means the Gulf is heating up. Thanks.


Yesterday.....


Member Since: June 9, 2005 Posts: 23 Comments: 37858
909. Cavin Rawlins
3:35 PM GMT on June 11, 2009
Quoting Vortex95:
Upper level winds will fall starting when?


When the upper low secludes. The consensus is 3-5 days but one must not look at a specific date but look at the behaviour of the trough.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
908. Patrap
3:35 PM GMT on June 11, 2009
907. AllWeatherFriend
3:32 PM GMT on June 11, 2009
How are the temperatures in the Gulf of Mexico at this time of the year? Are they warm enough for tropical storm development? I'm asking because the forecast for the next five days will be approaching the mid-90's and usually that means the Gulf is heating up. Thanks.
Member Since: August 21, 2003 Posts: 19 Comments: 58
906. IKE
3:32 PM GMT on June 11, 2009
Quoting Vortex95:
Upper level winds will fall starting when?


If you believe the latest NAM...within 24-36 hours that trough/ULL is suppose to lift to the NE.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
905. Cavin Rawlins
3:31 PM GMT on June 11, 2009
Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
903. TampaSpin
3:29 PM GMT on June 11, 2009
901. Weather456 11:26 AM EDT on June 11, 2009
The cloud pattern clear defines the surface trough


Yep for sure......something could develop out of this in 4 days or so also....

Member Since: September 2, 2007 Posts: 178 Comments: 20439
902. IKE
3:29 PM GMT on June 11, 2009
GFS 12Z now...look at the dip showing the ULL.....just east of Florida...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
901. Cavin Rawlins
3:26 PM GMT on June 11, 2009
The cloud pattern clearly defines the surface trough

Member Since: July 24, 2005 Posts: 407 Comments: 19076
900. IKE
Quoting Drakoen:


It's not really something you can see by looking at visibles. It's that broad.


I can see a spin.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


When there's about 3 hours worth of visibles, then I can see it.


It's not really something you can see by looking at visibles. It's that broad.
Member Since: October 28, 2006 Posts: 57 Comments: 30491
898. IKE
Just east of that main vorticity.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
897. IKE
Quoting Drakoen:
Observations support a broad circulation. Upper level winds remain unfavorable for development.


When there's about 3 hours worth of visibles, then I can see it.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
local NWS indicated something possible for end of the weekend or beginning of next week,possible low of the east coast,but they are not commiting themselves to what.
Member Since: Posts: Comments:
Quoting KEHCharleston:

In order to be in a typical location for June, it would need to move a fair distance west and a wee bit north.

Would be right on for July though, right where she sits at the moment.


YOu can already see the Shear dropping and possible LL Spin developing.....it shows up also on the 850mb Vorticity...




Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting TampaSpin:
877. KEHCharleston 10:55 AM EDT on June 11, 2009
Shear will decrease at 9N 52W by tomorrow.


Yep your correct....I know it is very unusual for something to develop in that location...I don't see it happening until it gets to the Caribbean as i stated yesterday in my update...But, yes Shear will be dropping big time in the Tropics.....

In order to be in a typical location for June, it would need to move a fair distance west and a wee bit north.

Would be right on for July though, right where she sits at the moment.
Member Since: August 19, 2008 Posts: 6 Comments: 2490
892. beell
06Z GFS 200-850mb vertical shear

Values are in "meters per second" Mutiply by 2 to get approximation in knots.
Member Since: September 11, 2007 Posts: 143 Comments: 16649
Observations support a broad circulation. Upper level winds remain unfavorable for development.
Member Since: October 28, 2006 Posts: 57 Comments: 30491
Quoting TampaSpin:


Hey my freind! Looks like Big Papa is heating up.....


Yeh, a little bit,we'll just have to wait and see
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Quoting NEwxguy:
884. Ike,good one!!


Hey my freind! Looks like Big Papa is heating up.....
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884. Ike,good one!!
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884. IKE 11:04 AM EDT on June 11, 2009

Darn thanks IKE it could not figure out was was flapping behind me......LMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20439
On the road again.....
Member Since: August 19, 2008 Posts: 6 Comments: 2490
877. KEHCharleston 10:55 AM EDT on June 11, 2009
Shear will decrease at 9N 52W by tomorrow.


Yep your correct....I know it is very unusual for something to develop in that location...I don't see it happening until it gets to the Caribbean as i stated yesterday in my update...But, yes Shear will be dropping big time in the Tropics.....
Member Since: September 2, 2007 Posts: 178 Comments: 20439
884. IKE
Quoting TampaSpin:
871. Orcasystems 10:49 AM EDT on June 11, 2009
Quoting TampaSpin:
9N 52W will become the first Named Storm of the year....Good Morning everyone


You mean the little blob under 35 knots of shear?


Orca did i say it was going to develop in that location.....You Question everything i say on here even if i said i was going to the JOHN i would believe....People are really getting very tired of your attacking!




Member Since: June 9, 2005 Posts: 23 Comments: 37858
871. Orcasystems 10:49 AM EDT on June 11, 2009
Quoting TampaSpin:
9N 52W will become the first Named Storm of the year....Good Morning everyone


You mean the little blob under 35 knots of shear?


Orca did i say it was going to develop in that location.....You Question everything i say on here even if i said i was going to the JOHN i would believe....People are really getting very tired of your attacking!

Member Since: September 2, 2007 Posts: 178 Comments: 20439
Just curious, is it tryin 2 develop a eye circulation??

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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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