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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roflmao
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Quoting kmanhurricaneman:
canesrule1 too much time on yur hands,your bored huh!!!
very bored, next im going to start asking if you give money o the homeless, lol.
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bottled
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canesrule1 too much time on yur hands,your bored huh!!!
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1178. IKE
2009 missing bloggers....

eye(downcaster)
edie(school canceled blogger)
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Quoting kmanhurricaneman:
unless the shear subsides there will be no development period. so guys its useless talking about TD OR TS or whatever IMO, LOL


Shear tendency are decreasing.
Member Since: July 8, 2005 Posts: 259 Comments: 23892
Quoting kmanhurricaneman:
COCONUT WATER
i like it too, but for real what do you prefer?
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Quoting canesrule1:
feel free to answer thanks, who here prefers bottled water over tap water?
COCONUT WATER
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1174. Relix
Quoting TheCaneWhisperer:
More on Puerto Rico Earthquakes.


Interesting read =). Thank you!
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Quoting kmanhurricaneman:
unless the shear subsides there will be no development period. so guys its useless talking about TD OR TS or whatever IMO, LOL


Yeah that is hilarious....and shear is expected to subside, so...
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feel free to answer thanks, who here prefers bottled water over tap water?
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unless the shear subsides there will be no development period. so guys its useless talking about TD OR TS or whatever IMO, LOL
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Quoting P451:
A lot of shear over a couple of blobs without surface reflection and we have arguments already? Come'on fellas you're better than this. I know we're bored and all but jeez breathe a little.


LOL.....if you read my Blog i said it would develop in the Caribbean....Never have i said the blob in the Atlantic would develop there...i do believe an Invest will be coming Tomorrow for the Atlantic Blob.

TampaSpins Tropical Update

IM out for a while....gonna do my 15miles......NO FIGHTING KIDS!
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1169. Levi32
Quoting Weather456:
The wave east of the antilles will probaly bring the wettest conditions of the season


You're more familiar with tropical waves than I am, so correct me if I'm wrong, but I figured the area of upper convergence and subsidence currently over and SE of the windwards would limit shower activity as the wave passes through the islands?
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More on Puerto Rico Earthquakes.
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Quoting futuremet:
According to 12z CMC, NOLA will get nailed.


Good afternoon everyone.

That sure is a shift to the east. Yesterday I mentioned that my local NWS, Lake Charles said the high would migrate east. But the 2 NWS on either side of here, HOUS AND N.O. said the high would remain strong. Now since there is some doubt as to the strength of the high Lake Charles said it would hold strong. LOL. Sometimes I wonder if they are guessing as much as I do???
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The wave east of the antilles will probaly bring the wettest conditions of the season
Member Since: July 24, 2005 Posts: 407 Comments: 19076
No invests as of this model cycle...guess we'll have to wait until after 8 EST to find out.
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1163. DDR
Quoting pottery:
DDR, close. Chickland/Caparo rd. Chickland village, just past the playing field.

Cool,well 'yuh los meh dey' lol
Got to run,talk to you all later.
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1161. beell
The TampaSpin wave does look pretty good!

Still not certain if the season long upper trough will lift-maybe just continue to take on more of a positive tilt. Effectively moving the base to the west. Leaving the Caribbean quiet.

Sign me up!
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Quoting Patrap:
Gas,Politics and weather all in one Post.

Priceless..


war, illegals,
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Quoting kmanhurricaneman:
kmanislander whats your take on that ull clearly its taking adive between the high and the trough something is setting up here , how do you think its going to play out?


It appears to be making a move to the WSW but ever so slowly. If it does it would provide an outflow channel to the NW for the broad low South of Jamaica as well as significantly reduce the SW shear now evident in that area.

Conditions could thus become more favourable for development once the ULL retrogrades to the general area of the Gulf of Honduras.

I have not concluded for sure that it is in fact moving in that direction but it appears that way to me.
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Quoting canesrule1:
still no new descending QuikSCAT pass.


You wont get new QS data for another few hours.
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1157. IKE
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Quoting RitaEvac:
Pretty broad and thats not good, means big system to come


It also means it will take longer to organize and spin up.
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1155. Patrap
Gas,Politics and weather all in one Post.

Priceless..
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1154. pottery
DDR, close. Chickland/Caparo rd. Chickland village, just past the playing field.
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still no new descending QuikSCAT pass.
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Witnessing the very beginning of the system, trough split, low levels now turning, then a fixed center low will take shape, then keep getting sheared, slowly get organized, keep getting sheared and so on
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JRRP,

I have a tropical wave train chart on my blog. It's a new porduct that will show official and unofficial african waves and will updated 0000 UTC everyday.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Ossgss, I remember when people use to pump your gas and given you something free, Then they paid you a dime a gallon to pump your own gas. No charges on atm or cash advances. As long as we have the same people running this country D or R paid by big companies, you'll get what they paid for and like it as judge Smell's would say. To much shear all over Atlantic just to stay on topic.
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Quoting TXGulfCoast:
See, the good thing about global warming is that all you folks in S. Florida will be able to watch your HD channels. Right? ROFL :)
hell yea!!
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kmanislander whats your take on that ull clearly its taking adive between the high and the trough something is setting up here , how do you think its going to play out?
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1147. DDR
Quoting pottery:
DDR, we have pipe, but this is UNC territory. So.........

Hmmm...i see,freeport mission road right?
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1146. pottery
My wife says she is going to write a novel, about Misfortune, Horrors, Woe and Doom, and call it "Withering Heats", because of this weather.......
Sounds vaguely familiar.
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See, the good thing about global warming is that all you folks in S. Florida will be able to watch your HD channels. Right? ROFL :)
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Conditions are unfavorable, but should be by tomorrow afternoon.



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1143. JRRP
Africa

225.42 mm 8.87 Inches
just in 5 hrs
Member Since: August 16, 2007 Posts: 0 Comments: 5725
Quoting RitaEvac:
check out that vort at 73W 30N
i see it an it looks impressive.
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1141. Patrap
Yup..."trough split" has been carved in our Foreheads,..like some new found revelation

LOL
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1140. pottery
DDR, we have pipe, but this is UNC territory. So.........
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Quoting RitaEvac:


thats why NHC doesnt have a low but there is rotatation defintely
i agree you clearly can see a spin in the lower levels.
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check out that vort at 73W 30N
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when he said he was leaving to Europe for two weeks with no updates to this blog and something forms in the tropics we can easily get 10-15 thousand posts EASY!
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1136. Levi32
Quoting Vortex95:
weren't you talking about a trough split a few days ago Levi?


I've been talking about it since June 3rd.
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Quoting canesrule1:
I think its about time for Dr.Masters to update his blog.
Quoting RitaEvac:


Its not there, its just a broad spinning circulation


thats why NHC doesnt have a low but there is rotatation defintely
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1134. Patrap

Atlantic GOES-12 WV big Loop
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1133. pottery
Trinidad weather now:- @ the airport
temp 93 f (smoke)
cloud ceiling 100,000 meters

that says it all........

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I think its about time for Dr.Masters to update his blog.
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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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