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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so we probably wont see anything tropical until july
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Invest coming soon....IMO
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Quoting extreme236:


That thing east of the Antilles? Unlikely at the moment.
yes that AOI, to us it looks relatively good but its under a lot of shear though, we are watching it closely though.
1029. sfla82
Its looking more amd more like 1992 everyday....Dead out there! We all knew it was going to be a very slow year though!
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1028. Levi32
Quoting heliluv2trac:
when is the high in the gulf suppose to shift east


It will likely oscillate eastward over the north gulf coast when the TUTT lifts out in 4-5 days, and then back to the west a little bit.
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Quoting gordydunnot:
Hey, I guess I made a prediction but only meant to have some people take a look at it. I figured the experts would set me straight.


Your only a day late........LOL...its all good.
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Quoting canesrule1:
dont think so, to me its doing a shift to the north but that my opinion, i think this just might develop. IMO


That thing east of the Antilles? Unlikely at the moment.
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when is the high in the gulf suppose to shift east
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Quoting canesrule1:
REMEMBER. DO NOT GET YOUR HOPES UP WHEN YOU SEE THIS BLOB IN THE CARIBBEAN FLARING UP BECAUSE AS YOU HAVE WITNESSED MANY TIMES BEFORE THEY DIE JUST AS QUICKLY AS THE CONVECTION FLARES UP.
sorry about the caps i didn't notice i pressed it.
Hey, I guess I made a prediction but only meant to have some people take a look at it. I figured the experts would set me straight.
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REMEMBER. DO NOT GET YOUR HOPES UP WHEN YOU SEE THIS BLOB IN THE CARIBBEAN FLARING UP BECAUSE AS YOU HAVE WITNESSED MANY TIMES BEFORE THEY DIE JUST AS QUICKLY AS THE CONVECTION FLARES UP.
1021. 7544
Quoting Vortex95:
I would rarely discount the GFS especially when said blob is there but as you have all said the GFS has had quite a bad start this year. Question: GFDL runs start only when it is called a TD or an invest?


as far as i know yes and dont forget hurricane lol
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1020. Levi32
Quoting Vortex95:
I would rarely discount the GFS especially when said blob is there but as you have all said the GFS has had quite a bad start this year. Question: GFDL runs start only when it is called a TD or an invest?


Yes they run for invests.
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Quoting canesrule1:
dont think so, to me its doing a shift to the north but that my opinion, i think this just might develop. IMO. but right now you are absolutely correct.
Quoting gordydunnot:
Your right 1007 but it looks to be moving n of west



As Tampa Spin indicated, maybe when it get's into the Central Caribbean. Even if it does clear SA, the notorious "Dead Zone" will keep it at bay.
Quoting TheCaneWhisperer:
Anything below 10N is going to have a hard time gaining elevation to clear South America and the "Dead Zone" at this point.
dont think so, to me its doing a shift to the north but that my opinion, i think this just might develop. IMO
1015. JRRP
Quoting gordydunnot:
I think I got one this time look at 8n 52 west nhc visible central Atlantic. I see developing T.D. Watch out Pottery.

take it easy.....
Member Since: August 16, 2007 Posts: 0 Comments: 6213
The Heat Index here in Savannah hit 110 yesterday. Today it's at 105. How high will it go?

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Your right 1007 but it looks to be moving n of west
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1011. Levi32
Quoting 7544:
this has changed from yesterdays run now it takes further east right over guess where

Link


The GFS has been out to lunch on this system for many many days now. All the other models take it slower and further south, which makes more sense. That's not a guarantee, but like I said to weatherwatcher12, even if it goes right over Jamaica the main impact will be rain. This isn't going to be a TS when it passes them. Only slow development, if any, is expected.
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1010. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213
Quoting 7544:
this has changed from yesterdays run now it takes further east right over guess where

Link
whats new??? well, me in miami I would welcome the rain with open arms!!!
The outflow looks good
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1006. 7544
this has changed from yesterdays run now it takes further east right over guess where

Link
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Quoting gordydunnot:
I think I got one this time look at 8n 52 west nhc visible central Atlantic. I see developing T.D. Watch out Pottery.
really you believe TD, your one hopeful mister.
Quoting 7544:
invest by tomorow ?
60/40 i'm leaning towards yes but anything could happen in 24 hours trust me.
I think I got one this time look at 8n 52 west nhc visible central Atlantic. I see developing T.D. Watch out Pottery.
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Quoting weatherwatcher12:

very cloudy and rainy. Can you give me a direction of movement in the near future please?


I wouldn't expect a direct movement over your area, but definatly nearby. It also depends on how soon, if at all, this system were to develop.
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Quoting Levi32:


That has something to do with the website......the real pass time is the purple times on the bottom of the image, above the time you're talking about. It says 22:59....that was yesterday.
ohhh, thank you for informing me.
1000. 7544
invest by tomorow ?
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Montego Bay, JM (Airport)
Updated: 16 min 54 sec ago

86 °F
Partly Cloudy
Humidity: 84%
Dew Point: 81 °F
Wind: 18 mph from the ENE

Pressure: 29.82 in (Falling)
Heat Index: 102 °F
Visibility: 6.2 miles
UV: 17 out of 16
Clouds:
Few 2000 ft
Few 2200 ft
(Above Ground Level)
Elevation: 10 ft
Quoting chessrascal:
This blob is getting some pretty strong convection.


Shear went from 50 to 40kts. So instead of a 747 plowing through it, it's now a 727. We'll talk when a Cessna is in the air, lol.
That's odd, someone said earlier today that the AOI was almost dead, but now that person is saying it may be an invest!
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Quoting canesrule1:
but how come it says 16:23 UTC that's about an hour ago hear in Miami.


That has something to do with the website......the real pass time is the purple times on the bottom of the image, above the time you're talking about. It says 22:59....that was yesterday.
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Quoting weatherwatcher12:

very cloudy and rainy. Can you give me a direction of movement in the near future please?


Northwest, towards the coast of central America, or just north of there. Keep in mind that rapid development of this system is very unlikely here, and even if it were to go directly over you the main issue would still be rain.
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Quoting hurricanemaniac123:
Bothe AOIs look pretty good. I think some invests might be coming.

I also think we might have TD 2 or TS Ana by next week.
possibly.
Quoting Levi32:


That's from 7pm EDT last night....this is the most recent one from 8:30am EDT this morning:

but how come it says 16:23 UTC that's about an hour ago hear in Miami.
Bothe AOIs look pretty good. I think some invests might be coming.

I also think we might have TD 2 or TS Ana by next week.
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Quoting extreme236:


Jamaica will feel impacts of this, yes.

very cloudy and rainy. Can you give me a direction of movement in the near future please?
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Quoting weatherwatcher12:
Any chance this could impact Jamaica


Probably not directly. Most of the models take it well to the southwest of you. The main impact for Jamaica will be rainfall.
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Quoting weatherwatcher12:
Any chance this could impact Jamaica


Jamaica will feel impacts of this, yes.
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Quoting chessrascal:
This blob is getting some pretty strong convection.
yes, looks good, dont want to be a wishcaster or downcaster but we might have an invest.
Quoting canesrule1:

Broad but closed circulation by the quikscat at 12:23 pm EST.


That's from 7pm EDT last night....this is the most recent one from 8:30am EDT this morning:

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Any chance this could impact Jamaica
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the blob that wouldnt die....
Member Since: June 29, 2007 Posts: 0 Comments: 1136
Current look:

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Broad but closed circulation by the quikscat at 12:23 pm EST.
This blob is getting some pretty strong convection.
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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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