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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1382. gator23
Quoting Acemmett90:

For all i care it hit made it direct hit one the west coast and then made its exit through wpb that is not a direct hit


Katrina didnt make a direct hit on NO for that matter
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You would think the grammar and such for a weather blog would be a bit better, but yet I still find myself having to sit there and reread some posts over and over again to determine what they are saying. Not trying to be a police about it but I mean come on its a bit annoying.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
3 days



5 days

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1379. Patrap
4 Orbits..notice the time in between passes.
Orbital Mechanics should be applied to Met classes..

Larger IMAGE

Member Since: July 3, 2005 Posts: 426 Comments: 129093
1377. Patrap
Wow..3 Bloggers all with their own respective Blogs,but all their posts are here.

Kinda like Blogcasting..High School Style
Member Since: July 3, 2005 Posts: 426 Comments: 129093
The blob seems to be a quasi-Fay scenario. However, Fay looked more defined and was not aided by upper level diffluence.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting hurricaneseason2006:


Sorry. I have to respect your decision.


No worries. I might reconsider in the future.
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18Z

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Quoting futuremet:
lol Can't stop looking at that water vapor imagery. The blob looks like it has spiral bands.


I have been seeing that for the past 4 hours. I say give it another 12 hours and NHC will call it an Invest.??
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1371. Levi32
Quoting heliluv2trac:
so the nam is not a reliable model which do you trust the most and thanks for the info


The NAM was not designed for tropical weather, and therefore is usually discounted by tropical forecasters. The only reason I have mentioned it the past few days is because it was handling the upper-air evolution much better than the GFS, which has been awful with this system almost from the beginning.

In general, though, the GFS is better than the NAM at most things.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
lol Can't stop looking at that water vapor imagery. The blob looks like it has spiral bands.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
so the nam is not a reliable model which do you trust the most and thanks for the info
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1364. Drakoen
Quoting futuremet:
Hey Draky, what is your take on this so far?


Model look confused on what they want to do with this system. Wait and see.
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1363. hydrus
If all the houses in your area dont have any roofs on them and did not get the eye,whats that called,a near hit?
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Very discreet there 456.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting hurricaneseason2006:
Good Afternoon W456, I might be stepping out of place but when I asked about the featured blogger, why did you turned down the offer?


What is the purpose of mail if you gonna do that. I turned down the offer because I was satisfied with where my blog stood. Mr. Masters already knows.
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1360. Levi32
Quoting heliluv2trac:
what model is that


That's the NAM that Ike just posted. I'm showing how it's moving the low northward too fast and strengthening it unrealistically.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Quoting Acemmett90:

For all i care it hit made it direct hit one the west coast and then made its exit through wpb that is not a direct hit


Um, if something moves over a town directly, that would be a direct hit lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
850 vort

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what model is that
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1355. Levi32
Quoting Levi32:


Not in a million years.



All you gotta do is look at the 200mb map. The NAM has fallen into the GFS fantasy of forming TCs on the heals of the sub-tropical jet before it has a chance to leave. You don't see tail-gating like that very often in the tropics.

Member Since: November 24, 2005 Posts: 635 Comments: 26684
1352. IKE
Quoting heliluv2trac:
2009 LOL


Yes.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting IKE:
NAM @66 hrs. cruising a low toward the Yucatan channel...believe it?



I can believe a low, but I'm skeptical if that will be a tropical cyclone though.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1350. Levi32
Quoting IKE:
NAM @66 hrs. cruising a low toward the Yucatan channel...believe it?



Not in a million years.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
1349. IKE
NAM @66 hrs. cruising a low toward the Yucatan channel...believe it?

Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting Acemmett90:

still not considered an actual direct hit
its the word direct thats important


Uh, Wilma's eye went directly over WPB. How is that not considered a direct hit? Unless I'm missing something...

Plus, Jeanne and Frances gave WPB hurricane force winds, so I don't think they really dodged the bullet from those. But, I guess you're right in a way, I don't think WPB has been hit directly from the east coast (but neither has Broward, Tampa, and many other places for that matter).
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2009 LOL
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1346. IKE
Quoting heliluv2trac:
are there any models indicating a ts before the end of june


What year?
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Blobby looks nice on water vapor.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting weatherblog:


LOL, even if this were to go to Florida I don't think conditions would be favorable for anything more than a weak TS. Plus, it would probably have land interaction with Cuba and/or the Yucutan.


exactly
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Acemmett90:

Jennie HIt miami, willma hit the west coast and Frances hit the Stuwert and Port St lucie so frances was the closest but still wpb is due for a direct hit


Jeanne hit the same place Frances hit (not even close to Miami) and Wilma did hit the west coast but her eye went directly over Broward/WPB.
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are there any models indicating a ts before the end of june
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Quoting canesrule1:
yes, i say INVEST! INVEST! INVEST!!!! LOL.


I didnt realize how much you remind me of someone until today. Wow, calm down a little for your namesake at least
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Quoting Levi32:


That's just an upper-level circulation at the base of the upper trough.


Ok Thanks. That's what I thought.
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Quoting extreme236:


Act as though you just dodged a Cat 5 hurricane


LOL, even if this were to go to Florida I don't think conditions would be favorable for anything more than a weak TS. Plus, it would probably have land interaction with Cuba and/or the Yucutan.
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Station 42058 - Central Caribbean Image


15.093 N 75.064 W (15°5'33" N 75°3'52" W)




Conditions at 42058 as of
1950 GMT on 06/11/2009:
Unit of Measure: Time Zone:


5-day plot - Wind Direction Wind Direction (WDIR): E ( 90 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 17.5 kts
5-day plot - Wind Gust Wind Gust (GST): 19.4 kts
5-day plot - Wave Height Wave Height (WVHT): 6.2 ft
5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 7 sec
5-day plot - Average Period Average Period (APD): 5.1 sec
5-day plot - Mean Wave Direction Mean Wave Direction (MWD): ESE ( 102 deg true )
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.84 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.07 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 79.0 °F
5-day plot - Water Temperature Water Temperature (WTMP): 81.5 °F
5-day plot - Dew Point Dew Point (DEWP): 73.0 °F
5-day plot - Heat Index Heat Index (HEAT):
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1335. Levi32
Quoting marknmelb:
Is there a little rotation going on just south of Andros off the NE coast of Cuba? Or just some back spin off the trailing edge of the front?


That's just an upper-level circulation at the base of the upper trough.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
1334. Ossqss
Interesting info on bottled water. I wonder how many of us have already paid bottled water prices for Tap water. Cane, who sponsered that taste test?

Quote

Only 25 percent of bottled water comes from municipal sources. The remaining 75 percent of bottled water sold in the U.S. comes from natural underground sources, which include springs and wells.


Link
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Quoting Weather456:
1321. futuremet,

yea I've already blamed the upper forcing for the pattern in convection.


lol I just felt like saying something
Member Since: July 19, 2008 Posts: 43 Comments: 4051

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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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