How much will global sea level rise this century?

By: Dr. Jeff Masters , 02:49 PM GMT am 13. Juli 2009

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How much will global sea level rise this century? Well, global sea level rise began in the late 1700s, and accelerated to 1.2 inches (3 cm) per decade over the past 25 years (see my post, Sea level rise: what has happened so far). If the conditions that led to this acceleration continue, we can expect sea level will rise an additional 1.1 ft (0.34 m) by 2100 (Jevrejeva et al., 2008). At a minimum, sea level rise during the 21st century should equal that of the 20th century, about seven inches (0.6 ft, 0.18 meters). This is the lower bound given by the IPCC in its 2007 assessment, which projected sea level rise of 0.6 - 1.9 ft (0.18 - 0.59 m) by 2100. However, they cautioned in their report that due to the lack of knowledge about how melting glaciers behave, the actual sea level rise might be higher. There is a growing consensus that the 2007 IPCC sea level rise estimates are much too low.


Figure 1. Observed global sea level from tide gauges (red line, pink color is the uncertainty range) and satellite measurements (green line), with forecasts for the future. The blue colors show the range of projections for three different forecasts (the forecasts overlap, but this overlap is not shown). Image modified from U.S. EPA.

The 2007 IPCC report: too conservative?
Three major sea level rise studies published since the 2007 IPCC report have argued that the IPCC's projections of sea level rise are too conservative. A paper published in 2008 in Science by Pfeffer et al. (2008) concluded that the "most likely" range of sea level rise by 2100 is 2.6 - 6.6 ft (0.8 - 2.0 meters). Their estimates came from a detailed analysis of the processes the IPCC said were understood too poorly to model--the ice flow dynamics of glaciers in Greenland and Antarctica. For example, increased glacial flow may result when water draining from melt water lakes on the surface of the glacier to the base of the glacier, where it acts as a lubricant. The authors cautioned that "substantial uncertainties" exist in their estimates, and that the cost of building higher levees to protect against sea level rise is not trivial.

Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany looked at the observed relationship between changes in sea level and global temperatures since 1900 (Rahmstorf, 2007). Rahmstorf showed that that there has been a direct relationship between sea level rise and global average temperature: 0.1 - 0.3 meters of sea level rise occurs per °C increase in global temperature. Using this relationship, Rahmstorf predicted 1.6 - 4.6 ft (0.5 - 1.4 m) of sea level rise by 2100, since the IPCC predicts that global temperatures will rise 1.4° to 5.8°C. Rahmstorf concluded, "very low sea-level rise values as reported in the 2007 IPCC report now appear rather implausible in the light of the observational data".

A similar approach was taken by Grinsted et al. (2009), but they extended the relationship between sea level and global average temperature all the way back to 200 A.D. using proxy records. They concluded that ice sheets respond more quickly to temperature changes than the computer models used in the 2007 IPCC assessment. The authors estimated that "IPCC projections of sea level rise 2090 - 2099 are underestimated by roughly a factor of three". The authors predicted that global sea level will be rising 11 mm/year by 2050--four times faster than the 20th century rise. By the last decade of this century, they forecasted that sea level will rise 3.0 - 4.3 feet (0.9 - 1.3 meters), using the IPCC's A1B "business as usual" scenario.

The long-range forecast: using paleohistory to forecast sea level rise
We can also look at times in Earth's past that had similar climate to what we expect by the year 2100. The best time to look at is probably just before the most recent ice age--the Eemian. This interglacial period 130,000 - 114,000 years ago featured temperatures near the poles that were 2°C warmer than present-day temperatures. Tree line lay about 500 miles farther north in the Canadian Arctic, and the hippopotamus ranged as far north as the Thames River in England. A similar climate is expected under some of the more moderate global warming scenarios envisioned by the IPCC. Sea level is believed to have been 4 - 6 meters (13 - 20 feet) higher than at present during the Eemian, but there is at least one unpublished study that presents evidence that global sea level was 6 - 9 meters (20 - 30 feet) higher. If the climate does warm to levels seen in the Eemian, it is widely believed that we would again see sea levels at least 4 - 6 meters higher than the present-day levels. Clearly, sea level rises of this magnitude would be ruinous to society. However, most climate change scientists believe that it would take many centuries for enough ice to melt from the Greenland and West Antarctic ice sheets to create sea level rises of 4 - 6 meters.

However, the scientist who is arguably the most visible and authoritative climate scientist in the world, Dr. James Hansen of NASA, stated (Hansen, 2007) "I find it almost inconceivable that business-as-usual climate change would not yield a sea level change of the order of meters on the century timescale" (IPCC business-as-usual (BAU) scenarios assume that emissions of CO2 and other greenhouse gases will continue to increase year after year). Hansen gave a hypothetical but potentially realistic scenario where the sea level rise due to ice sheet disintegration doubles every decade, leading to a 16 foot (5 meter) sea level increase by 2100. He noted that during the Plio-Pleistocene period 2 - 3 million years ago, CO2 levels were similar to today (350 - 450 ppm), and global temperatures were 2 - 3°C warmer, similar to what we expect by the end of the century. Yet, this Plio-Pleistocene world was "a dramatically different planet, without Arctic sea ice in the warm seasons and with a sea level 25 ± 10 m higher."

Summary
To summarize, here are some predictions of how high global sea level might rise by 2100:

0.6 ft (0.18 m): Constant linear rise, equal to 20th century rise
1.1 ft (0.34 m): Constant acceleration model (Jevrejeva et al., 2008)
0.6 - 1.9 ft (0.18 - 0.59 m): Primitive models of ice sheets (IPCC, 2007)
1.6 - 4.6 ft (0.5 - 1.4 m): Relationship between temperature and sea level rise since 1900 (Rahmstorf, 2007)
3.0 - 4.3 feet (0.9 - 1.3 m): Relationship between temperature and sea level rise since 200 A.D. (Grinsted et al., 2009)
2.6 - 6.6 ft (0.8 - 2.0 meters): Considering glacier ice flow dynamics not included by the IPCC (Pfeffer et al., 2008)

In a 2009 interview with New Scientist magazine, sea level expert Stephan Rahmstorf said, "I sense that now a majority of sea level experts would agree with me that the IPCC projections are much too low." This sentiment was echoed by glaciologist Robert Bindschadler of the NASA Goddard Space Flight Center in Greenbelt, Maryland, who commented, "most of my community is comfortable expecting at least a metre by the end of this century."

In forthcoming posts in this series, I'll explore how a meter (3.28 feet) of sea level rise will affect the U.S. coast, the Caribbean, and other vulnerable locations world-wide. It would be wise to begin preparing now for a potential rise in sea level of a meter this century. In particular, development near the coasts should be severely restricted in low-elevation zones. It will be very expensive to protect or move infrastructure away from rising seas later this century. However, even if the rate of sea level rise doubles every decade, those of us who are over the age of 50 will not live to see sea level rise cause a significant disruption to society. There is time for society to prepare for the rising sea.

References
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.

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.

Hansen, J., 2007, "Scientific reticence and sea level rise",, Environ. Res. Lett. 2 (April-June 2007) 024002 doi:10.1088/1748-9326/2/2/024002.

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.

Pfeffer, W.T., J.T. Harper, and S. O'Neel, 2008, "Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise", Science 321 no. 5894, pp. 1340-1343, 5 September 2008. DOI: 10.1126/science.1159099

Rahmstorf, Stefan. "Sea-Level Rise: A Semi-Empirical Approach to Projecting Future." Science 315 (2007): 368–370.

Other posts in this series
Sea level rise: what has happened so far
U.S. vulnerability to sea level rise

Wednesday, I'll take a look at the Atlantic hurricane forecast for the remainder of July. There's currently nothing out there worth discussing--will it stay that way?

Dr. Ricky Rood has some interesting commentary on the new climate change legislation that passed the House last month, and will go to the Senate in September.

Jeff Masters

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no go weather rule

best be safe then sorry
Member Since: Posts: Comments:
Quoting Weather456:


But too close to the islands, almost grazing us.


The 00Z and 12Z runs, which are traditionally more reliable, both had a more westerly tack. The 06Z and this 18Z have a more easterly/northerly track. So I would expect the models to wobble back and forth between those solutions.
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583. IKE
Quoting WeatherStudent:


Thank you, but you do not have to defend me, :). I've pretty muched gotten use to folks constantly ridiculing me on here.


The ignore feature helps. Nice of her to stand up for you.....
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Quoting Drakoen:
Very strong trough will likely recurve anything that tries to make a run for the eastern seaboard.


Yup, I think this what will actually happen. Most of the models agree with this too.
Member Since: Juli 19, 2008 Posts: 43 Comments: 4051
Quoting IKE:


At 156 hrs., it's looks it....



But too close to the islands, almost grazing us.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
Looks like a no go due to weather.
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578. IKE
Quoting NRAamy:
IKE...it was aimed towards WeatherStudent, and I have had it up to here with weather geeks bashing on him...you don't like what he has to say, boys? then put him on ignore...

sorry, IKE, this was not aimed at you....the tolerance level on here, or the lack thereof, is pathetic...


It's best to put them on ignore and move on.

Admin will start banning if this system spins up...
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not looking good on the launch at all today...
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Sheesh, somebody get NASA some better cameras. I think they've been using the same ones in the launch tower since the 1980s. Everything is so grainy and washed-out. While they're at it, maybe upgrade their launch computers, it looks like they still run DOS.
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575. IKE
Quoting Drakoen:
Very strong trough will likely recurve anything that tries to make a run for the eastern seaboard.


At 156 hrs., it's looks it....

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Quoting Dar9895:

yep.


Dar9895,

You from Saint Barts right?
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076


more storms popin up from the west northwest of orlando now
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IKE...it was aimed towards WeatherStudent, and I have had it up to here with weather geeks bashing on him...you don't like what he has to say, boys? then put him on ignore...

sorry, IKE, this was not aimed at you....the tolerance level on here, or the lack thereof, is pathetic...
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Very strong trough will likely recurve anything that tries to make a run for the eastern seaboard.
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Quoting IKE:
18Z GFS has it headed near...

20N
60W....

yep.
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possible no go for shuttle
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hurricaneseason2006, I'm really becoming ashame of you, knowing where you reside.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
566. IKE
Quoting Dar9895:

Maybe Ana, will pulled north of the Leeward Islands, interresting isn't it.


It's definitely latched on.
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565. IKE
Quoting NRAamy:
hurricaneseason2006....was that really necessary?


If he said something toward me, please abstain from quoting him.

I don't care what he says about me.
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aquak9...I'm workin' for Little Debbie Snack cakes at this point...

;)
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.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
hurricaneseason2006....was that really necessary?
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Amy- are ya working for peanuts or IOU's? I think I'd prefer the peanuts myself...
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The GFS is backing off the trough.....tsk...tsk..tsk.

Member Since: Juli 19, 2008 Posts: 43 Comments: 4051
Quoting IKE:
18Z GFS @ 120 hrs....


Maybe Ana, will pulled north of the Leeward Islands, interresting isn't it.
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557. IKE
Quoting GeoffreyWPB:


As I stated last night, the GFS has been spinning up Ana since late April. But I have to admit, this may have a shot at it.


Agree.
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Quoting stoormfury:
when it comes to initialising shallow systems the GFS always finds difficulty. the records are there


As I stated last night, the GFS has been spinning up Ana since late April. But I have to admit, this may have a shot at it.
Member Since: September 10, 2007 Posts: 0 Comments: 11538
554. IKE
Quoting NRAamy:
no....work until 5:15 PM.....

:(


Dang it...I guess wrong on that...I was close, but this ain't horseshoes!
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Quoting WeatherStudent:


Too close for comfort there, Ike.
it may get a lot closer than that yet WS but i be back after launch
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552. IKE
Quoting stoormfury:
when it comes to initialising shallow systems the GFS always finds difficulty. the records are there


GFS has latched on to this one....consistently.

May see the "A" storm...prepare crow for TAZ and IKE.
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no....work until 5:15 PM.....

:(
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when it comes to initialising shallow systems the GFS always finds difficulty. the records are there
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thanks Teddy...

:)
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548. IKE
Quoting NRAamy:
yo IKE.....it is slowwwwwwwwwwwwwwwww on here....


And you've got an hour left until your job is through for the day....you're on PDST and you get off work at 4:30 pm? Did I guess right?
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Quoting Weather456:
Anyone notice this yet



Well, whatta we have here...
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NRArmy. we're all watching the shuttle launch.
Member Since: Juli 8, 2005 Posts: 259 Comments: 24574
yo IKE.....it is slowwwwwwwwwwwwwwwww on here....
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542. IKE
18Z GFS has it headed near...

20N
60W....
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540. IKE
Quoting WeatherStudent:


Good evening, Ike.


Good evening.
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Can the GFS retain its integrity?
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
537. IKE
18Z GFS @ 120 hrs....

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something seems more than likely will be brewing in the tropical alt very soon
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Quoting KEEPEROFTHEGATE:
just like i said in your blog this morning 456 on post #1 its coming late tomorrow night sometime wed should have a invest if it maintains and builds itself


Very true, if it does continue over the next 24 hrs, then most likely an invest.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076

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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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