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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This blob is getting some pretty strong convection.
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I like it, how things are heating up, a organized tropical wave and a blob with deep convection.
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979. beell
No kidding!
Thanks
Member Since: September 11, 2007 Posts: 144 Comments: 16876
Atlantic Tropical Weather Outlook

000
ABNT20 KNHC 111140
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT THU JUN 11 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS.

$$
FORECASTER AVILA

Member Since: July 3, 2005 Posts: 426 Comments: 129093


Pressure got pretty low last night, but has gradually risen. Winds are steadily out of the east, but it looks like it is getting some squally weather right now.
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Quoting StormW:


Not enough coffee this morning!

I added the wave to my synopsis.


I haven't even started drinking coffee yet lol.

I added the wave to mine as well.
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Fascinating...

Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting beell:
959.
Maybe dug a little deeper to the SW?


Yeah that's the part that will get chopped off. The main trough is starting to lift, and a weak shortwave dropping down from the north will phase with the tail-end of the TUTT to form the cut-off upper low. At least that's what the models are saying.
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thanks DDR , i meant friday night into sat morning. if it were late july/ early august, this wave would be a matter of concern
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Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting TampaSpin:


Impressive looking, ain't it, TS?...LOL

GOES-12 Atlantic WV Wide view,animated Loop
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968. beell
959.
Maybe dug a little deeper to the SW?
Member Since: September 11, 2007 Posts: 144 Comments: 16876
967. DDR
Quoting stoormfury:
well organised atl tropical wave east of the southern windward islands. this should bring showery conditions to the islands later tonight into friday. unfavourable upper winds preclude y development. however the wave should be watched as it enters the caribbean, where conditions are forecast to be favourable the next few days

More likely friday night,that wave is at least 300+ miles from the islands right now,I'm looking forwrd to it though.
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Quoting WeatherStudent:


So, it's begining to progressively seperate itself from our area of tropical interest then, Levi32?


Beginning to, yes. It will take 72-96 hours for the process to complete though. TUTTs don't like to go anywhere fast.
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Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting Levi32:
Notice the eastward and northward shift of the upper trough.

12 hours ago:



Now (15z):



So, it's begining to progressively seperate itself from our area of tropical interest then, Levi32?
well organised atl tropical wave east of the southern windward islands. this should bring showery conditions to the islands later tonight into friday. unfavourable upper winds preclude y development. however the wave should be watched as it enters the caribbean, where conditions are forecast to be favourable the next few days
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Shear tendency



Monday's 900-200 mb shear

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Quoting StormW:


Thanks Tim...looked at it and forgot to put it in the darn sysnopsis.


Lol I forgot all about it too and didn't mention it.
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960. 7544
where will ana form

a in the carb. where our blob is now
b. at 9n and 52 west in the atl.
c. none not yet
who will win the battle
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Notice the eastward and northward shift of the upper trough.

12 hours ago:



Now (15z):

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And surface obs show a broad circulation

Member Since: July 24, 2005 Posts: 407 Comments: 19076
957. Relix
That blob better move away from PR! I want sun! =O
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956. IKE
Quoting Weather456:
last night to be exact

But this came out seconds ago:



Vort is continuing to increase.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
How about the entry?

Since that's what its for.

Potential sea level rise in Northern Europe resulting from global warming and the complete melting of the polar ice sheets

This video shows sea level from the present-day location to the level estimated if the Greenland and Antarctic ice sheets melt completely.

Member Since: July 3, 2005 Posts: 426 Comments: 129093
953. 7544
ill have to agree with tampa spin on where ana may form stay tuned
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Quoting Weather456:
last night to be exact


Is this the most interesting thing we can find to talk about? lol
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last night to be exact

But this came out seconds ago:

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The Disturbance still has some pretty deep convection as of 12:30 PM.
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Quoting CybrTeddy:


This one's quite old, but does show a Broad closed circulation



Yeah.....yesterday....

Lol.
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Quoting Levi32:


Well that pass was from 11:30UTC that's only 5 hours old.


This one's quite old, but does show a Broad closed circulation
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Quoting CybrTeddy:



QuickSAT missed the AOI though this run, because earlier that missed area had a broad closed circulation near by the disturbance,


Well that pass was from 11:30UTC that's only 5 hours old.
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Quoting Levi32:
QuikSCAT shows low-level turning north of Panama but no closed circulation.




QuickSAT missed the AOI though this run, because earlier that missed area had a broad closed circulation near by the disturbance,
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The world is now at the start of the 2009 influenza pandemic, says WHO Director-General Dr Margaret Chan
3 minutes ago from web
Influenza pandemic alert raised to phase 6
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came back from lunch, sitting here watching portlights video of their trip to volusia county, and all of a sudden I'm like "hey thats main street here in daytona" lol
They're Hereeeeee
Member Since: June 29, 2007 Posts: 0 Comments: 1136
Quoting StormW:
Good afternoon!

TROPICAL WEATHER SYNOPSIS JUNE 11, 2009 ISSUED 12:15 P.M. EDT


StormW did you look at 9N 52W closely...ANA will be coming from that i believe in about 5-7 days..
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting Weather456:
Tampa, sorry I did not get to update my blog on your site but I try to get the update there this aftrernoon and through the weekend.


Its ok my friend!
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QuikSCAT shows low-level turning north of Panama but no closed circulation.

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Tampa, sorry I did not get to update my blog on your site but I try to get the update there this aftrernoon and through the weekend.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
NEXRAD Radar
Nashville, Base Reflectivity 0.50 Degree Elevation Range





NEXRAD Radar
Nashville, Velocity Azimuth Display Wind Profile Range 124 NMI
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting jeffs713:

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)


Can you share the link with us? Thanks in advance
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RE:927. futuremet - Thanks!

I know many of you will find this discussion a bit boring, ho hum, and been there done that. I promise you there is someone else reading this blog that has wondered or been confused regarding the same things. Your answers and patience are much appreciated.

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 wondered that as well. Altitude and mb are inversely related, right? I see that you have explained why you use it... I am all for luck. Thanks jeffs713 for your input

MODIFIED
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Wind shear begins to weaken.

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Here was my Tropical Update from yesterday that i think today is even more Accurate...

TampaSpin Trooical Update
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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)
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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.