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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Since the beginning of the Decade we've seen 9 Category 5s, since 1999 we've only seen 2 EF-5s.
hahaha...but not for long.
Dr. Masters goes on vacation next week :)
1.15
succinct! bravo.
1.15
That SPC page reports in MPH, though.
Not that I really disagree with this, but I can't help but give climatology less emphasis in given recent years, but maybe this year will be different.
I disagree with this.
Named Storm coming on or before June 19th!
Hi Chicklit
Slow June so far with the usual convective " blow ups " ( aka BLOBS LOL )
Strong SW shear still rules N of Panama with no sign of easing. There is a pocket of low shear attempting to migrate down from the NW Caribbean and this could happen if we see the trough "cut off" as some of the models are calling for.
June 1st means nothing to mother nature. Just a date on the calender.
Agreed...Strong westerly shear blowing through the caribbean.
he is???
Until we see a sustained period of departure from the norm then, IMO , climatology as established cannot be substituted by a new norm.
We are in period of heightened activity and to that extent climatology must be modified but over the course of a season the last few years have largely held true to form. As they say, it is the exception that makes the rule.
There will be the odd anomaly, such as Bertha last year, but on the whole I don't think anyone can say there has been a radical shift in climatology.
Ha lol, sorry just not happening
Good points, but behavior with cyclones and their frequency (as you mentioned) haven't really followed along with climatology. Certainly something to pay attention to, but not the end all.
really????
well ....
I agree that climatology is but one tool in the dynamic of forecasting. No two years are ever the same given all the variables with atmospheric conditions, surface conditions etc.
That's what makes the watching and waiting so exciting.
Yup...interested to see what this season holds. El Nino will probably cap its storm total potential.
From Futuremet Productions:
Why is moist air less dense than dry air?
Original Script:
Okay, so why is moist air less dense than dry air? Would it more sense that drier is less dense since it is less concentrated than moist air?
In this tutorial, we will learn why moist air is less dense, because this baffles many forecasters.
In order to understand this, we need to know a little bit of basic chemistry, and need to know about diatomic elements. As most of us know, gases are extremely light and need to be in pairs to be more stable. There are seven diatomic elements and they are: H2, N2, O2, F2, Cl2, I2, Br2, which are: hydrogen, nitrogen, oxygen, fluorine, chlorine, iodine and bromine. The most common gases in our atmosphere are Nitrogen and oxygen. Now Oxygen has an approximate atomic mass of 16, and nitrogen has an approximate atomic mass of 14. Now because they are in diatomic (di=double) , the typical atomic mass for oxygen is 32, and is 28 for nitrogen.
Water Vapor H2O has an atomic mass of 18. That is because Hydrogen only has only an atomic mass of 1 since it is the lightest element, and remember, Oxygen has an atomic mass of 16. In a water molecule, there are two hydrogen atoms; one at each side of the large Oxygen atom. So by adding the two hydrogen atoms and the oxygen atom, we will have a total atomic mass of 18 (1 1 16). With an atomic mass unit of 18, H2O is much lighter than diatomic Oxygen (32) and Nitrogen (28). Therefore the more water vapor that is available, the more the density of the air will decrease. Due to the fact that moist air is lighter than dry air, it is more buoyant, and will rise if a dry air mass is pushing against it. A good example of why moist air is susceptible to vertical motion is when an inflated balloon is placed in a tank of water. The balloon will rise as it is being displaced by the denser liquid; it would still try to rise even if you push against it.
Dry Lines
Now let us what happens when dry and moist air are placed side by side.
A dry line is the perfect example of moist air being less dense than drier air. A dry line is a region of substantial moisture gradient, which means that the humidity changes significantly over a small distance. Mesoscale convective complexes, squall lines, and even supercells tend to be associated with dry lines. That is why veteran storm chasers always look for areas of strong moisture gradient to determine the instability. A dry line is somewhat quasi-baroclinic, since the dry air pushes against the lighter moister air, forcing it to rise. Even without the aid of cold fronts, they still have adequate instability to kindle thunderstorm formation.
There is some suggestion of a progression back to neutral. Yet one more "wait and see " issue this year.
We have a 3 day weekend coming up so please reprogramme those computers for next week !
That could make things even more interesting. One would thing that the borderline neutrality/El Nino will substantiate the theories of storms blowing up closer to land.
Hmm...interesting.
El Nino = less active
Of course, that only refers to numbers of storms, not intensity of the one that may come ashore in a major coastal metropolis.
Would seem that way with the computer models, but I think that I'll wait to see something evolve before buying into them. Doing this since the computer models have continued to suggest that 3 to 5 days out conditions would be favorable for cyclogenesis, but then when it comes 3 to 5 days time, there's absolutely nothing and the conditions didn't become favorable. Yes I recognize that early on I did consider the computer models when making my analysis, but I've become more and more skeptical as nothing the computer models have shown has come to fruition.
Well when I see the HPC begin mentioning cyclogenesis in their outlooks I tend to pay close attention. We do have a precursor disturbance east of Jamaica now...probably what will be the eventual low pressure system.
They seem a bit fickly :)
See my avatar for my reference.
Given the right time and the right conditions, a tropical cyclone will form regardless of the teleconnections. If a storm is there when conditions are favorable, cyclogenesis will occur which is what happened in 2004.
Just learning from the mistakes that I've made in doing my analysis and making observations the past couple days. Think, at least for me, it'd be easier to take a wait-and-see approach.
Of course its always good to be cautious, but this time it might be a reality.
while disasters such as localized wildfires and flooding don't have the media-wide sex appeal as a huge hurricane, they are still devastating to their victims...and afford us perfect opportunities to fulfill our mission:
Meeting the needs of un-served, under served and forgotten people...
...so...
Many thanks to everyone who is making this possible - from financial contributors to those who remember us in their thoughts and prayers to those who are going to be onsite working...
My view is that we are creating a movement here...and it's pretty cool to be a part of it...
www.portlight.org
do i smell JFV # 2???
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