Sea level rise: what has happened so far
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
Reader Comments
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I hope it was more beneficial than problematic.
True, but since microwaves generally excite water molecules, raising their temperature, it would take a while to just warm the water vapor. You would probably end up with a faster rate of heating by measuring the increased temp of surface water, or possibly increased evaporation. Considering the scales measured, the impact (at least in my mind) would be minimal at best.
Water vapor imagery shows you guys remain on the dry side of the discontinuity.
Yesterday's blog
What is somewhat guaranteed, is that deep layer moisture will spread north across Jamaica and Eastern Cuba over the upcoming week. Total amounts may exceed 1-2 inches with lesser amounts in the Caymans due their relative position to the features.
As the upper-surface features change over the upcoming days, so will the moisture distribution.
Isnt the atmoshpere already being bombarded with microwaves anyway? Any impact would be minimal at best IMO
THE PATTERN EVOLUTION/FORECAST OVER THE CENTRAL AND SOUTHERN
CARIBBEAN CONTINUES TO PUZZLE THE MODELS. CYCLOGENESIS AS THE GFS
FORECASTED HAS FAILED TO MATERIALIZED. IN EACH CYCLE THE GFS
DELAYS ONSET BY 12-18 HRS...AND THE LATEST RUN IS NOT THE
EXCEPTION. THE ECMWF CONTINUES TO FORESEE A MUCH SLOWER
EVOLUTION...AND THIS IS STARTING TO LOOK AS THE BEST OPTION. THE
EARLIEST WE MIGHT SEE A CYCLONE FORMING IS GOING TO BE AT 42-54
HRS...WITH A LOW FORMING NEAR SAN ANDRES ISLAND...TO THEN PULL
NORTH TOWARDS JAMAICA/THE CAYMAN ISLES BY 66-72 HRS. ALTHOUGH THE
SYSTEM IS SLOW TO DEVELOP...CONDITIONS FOR ORGANIZED CONVECTION
REMAIN FAVORABLE ACROSS JAMAICA-PORTIONS OF HAITI AND THE
SOUTHEAST COAST OF CUBA. IN THIS AREA EXPECT RAINFALL AMOUNTS OF
20-40MM/DAY AND MAXIMA OF 150-250MM. WE MIGHT SEE A LULL IN
ACTIVITY ON DAY 02...WITH ANOTHER SURGE ON DAY 03 AS THE SURFACE
CYCLONE BECOMES BETTER ORGANIZED. BUT OVERALL...THIS REMAINS A
HIGH UNCERTAINTY FORECAST
2050 GMT on 06/10/2009:
Unit of Measure: Time Zone:
Click on the graph icon in the table below to see a time series plot of the last five days of that observation.
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): 21.4 kts
5-day plot - Wave Height Wave Height (WVHT): 7.2 ft
5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 8 sec
5-day plot - Average Period Average Period (APD): 6.1 sec
5-day plot - Mean Wave Direction Mean Wave Direction (MWD): ESE ( 112 deg true )
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.80 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.06 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 83.1 °F
5-day plot - Water Temperature Water Temperature (WTMP): 81.9 °F
5-day plot - Dew Point Dew Point (DEWP): 75.9 °F
5-day plot - Heat Index Heat Index (HEAT): 91.2 °F
GOES-12 Atlantic Basin WV ,Wide view
From my post of 4:09 GMT much earlier today
"The models have not really handled the SW Caribbean well if you look at the last 7 days of runs. In particular, shear values have remained stubbornly high, thus preventing any development regardless of what the models have shown.
Shear has been on the rise for the past 24 hours in that area so we are at least 2 days or more away from any chance of something developing."
Sigh. The NWS Lake Charles said the high was going to migrate east. So I dont know if anyone in the gulf is out of the woods should something form. :(
MeteoStar might take issue with the star name.
iAnd iI iAm iPersonally iAwfully iTired iOf iThis iStupid iFad.
As I and some others have been pointing out about the GFS for the last several days. It's too fast (still is on the new 18z run btw), and has issues with handling the pattern. The ECMWF has been my model of choice for this situation since last week. It has been very consistent.
My videos are purely educational though...
My thoughts exactly. The time frame shear relaxes complies with the ECMWF. The GFS developed a closed low in a time frame quicker than shear is expected to relax.
Good point. Besides microwaves, it also gets bombarded by everything from neutrinos (which move at a significant fraction of the speed of light) to gamma radiation (more energetic than microwave), to infrared (translates more easily to heat... as it is well... heat.)
A massive solar flare / CME will have the effect of heating the atmosphere by a few degrees C over 2 years. doubt a satellite system can do anything close.
But it is slightly stronger on this run and aiming WNW...in general agreement with other models on path.
374 - there are over 888 Sat's with various outputs 24x7x365. Sorry to drag it into the discussion, but I am still curious.
Path yes.....timing no.
The NAM at 48 hours has the low east of Nicaragua, whereas the GFS has it clear up near Jamaica at that time, which as 456 pointed out is not in sync with the retreat of the upper trough and associated strong wind shear:
NAM 48 hours:
GFS 48 hours:
I dedicated my blog area to be a set of my personal favorite tropical links (without the need to deal with bookmarks on multiple PCs). It was entirely selfish, admittedly, but am happy to share.
http://www.wunderground.com/blog/atmoaggie/show.html
Match those with the 200 mb winds, the GFS remains unreasonable.
My opinion only, but I have no faith in the NAM with anything south of latitude 25 N.
OK, I never trust it with anything over water, either, but you get the point.
Exactly.
Not that I disagree with the analysis, you two, I just don't like NAM for the job of tropical forecasting...
Yeah I know everyone hates the NAM....it's not meant for the tropics, but it has been very good at handling the upper trough the last few days, and is beating the heck out of the GFS with the surface forecast. The fact that it's a high-resolution model has probably helped a lot in this pattern. So.....credit where it's due lol.
Neither do I, thats why I'm stressing more on the GFS relative to the ECMWF.
It would seem model consensus continues to materialize. The NOGAPS has the right idea on track.
Yesterday at 12Z
IF something forms, which seems more likely by the weekend.
Yes, it hit 90 today with dew point pushing 72. Horrible running weather.
You don't know that, more models are developing it, it is an area to watch at the very least.
The other possibility (not as likely but who knows) is it will take a more northerly track into Cuba and then the eastern GOM, Florida, or the Bahamas. Similar to Ernesto from 2006.
But right now I'm still not even sure we'll get a tropical cyclone even though it's looking more likely.
Just watch...I see how most on here are hardcore model forecasters. No one seems to VIV them. You got to look at what is in front of you. Look at the conditions upstream. How many times do the models change? Esspecially 5 or 6 days out?
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