How much will global sea level rise this century?

By: Dr. Jeff Masters , 14:49 GMT le 13 juillet 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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Quoting Acemmett90:

what state or city would you copair carlos to


Rhode Island.
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Quoting CybrTeddy:


Reminds me of Marco.


Yeah, that and Tracy were the two that immediately came to mind. But Marco's tropical storm force winds extended out only 15 miles from the center, whereas Carlos's extend out to 35 miles.

Either way, still a small storm, though Polo of last year was remarkably similar in latitude, intensity, and size to Carlos.
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Ace...what did you click on to get that graphic?
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I give this a 30% chance of being designated a TD within 12-14 days. I came to this conclusion by writing a series of numbers on a piece of paper. I then dropped a pen from an approximate height of 18 inches which consequently landed with its tip evenly between 20 and 40 *(there was no 30 designation). Since the pen was blue, and all other variables such as errant cat hairs were eliminated, I feel that this is as accurate a forecast as the 344 hour GFS model.
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Carlos is quite odd its been forming eyes all day but losing them in 15-30 minutes. Even the NHC is wondering what the deal is with this storm.
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Carlos is not as small as Marco the the BOC,
Marco was the smallest tropical cyclone ever recorded. Was the size of Orlando.
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Quoting KoritheMan:
Carlos is one of the smallest tropical cyclones I've seen since becoming an avid weather watcher in 2002:



Reminds me of Marco.
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Carlos is one of the smallest tropical cyclones I've seen since becoming an avid weather watcher in 2002:

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Impressive Acemmett where did you get that graphic from?
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Hey if this wave is as big as some say it may be, then maybe we will get an invest out of it in a day or two but as for now it is nothing but a patch of showers out in the ocean.
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Quoting Chicklit:
It's going to break out of the ITCZ...
Link


I could see that happening but right now everything is up in the air with this wave.
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It's going to break out of the ITCZ...if it hasn't already.
Link
From the 8'oclock NHC Discussion:
...ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 13N16W 10N23W 11N29W 8N35W 9N50W TO THE S AMERICA COAST NEAR 6N58W.
Goodnight! The weather will still be here in the morning!
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Okay yes NOGAPS and the GFDL push Carlos towards Hawaii
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Quoting MrstormX:


Ahy, but there likely was at least one cane those years also but there was no modern technology yo find them.


Very true.
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You should ask you folks to make Duffy's the local meeting place of WU members!
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If I recall there are still 2 models forecasting Carlos to brush closer with Hawaii but I could be mistaken.
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Quoting KoritheMan:


People are always beyond nuts on here. I don't think you were around during the 2007 season, but that season invoked hell on earth on this blog. I nearly left the site because of it.

Thankfully, that year, along with 2008, taught me a lot about tropical meteorology.


Good thing you stayed.
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Shear Map
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Quoting Acemmett90:
wpb i knew that i was just stating this this year the blog has become the movie one flew over the cokoo's nest lol


Your not old enough to know that movie!
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Quoting SLU:


well yeh .. it will bypass the northern islands over the weekend
At the time being, on its current pace, I don't believe it will pass north of the islands.
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Hi Ace...How many hours are we looking at with the GFS?
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Quoting KoritheMan:


Oh, there will be a hurricane, Taz. Only 1907 and 1914 saw no hurricanes.


Ahy, but there likely was at least one cane those years also but there was no modern technology yo find them.
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Quoting KoritheMan:


hunker, you seem to be one of the more knowledgeable people around here. With that said, what are your thoughts on this wave?
Wouldn't say I am one of the more knowledgable here but I thank you for the thought, I think :)

I have been through storms in SFLA for over 20 years and been following closely since Andrew. Everybody will have their own input whether from direct education or "street" knowledge and since the science of predicting these these storms does not always play out, all input can, and could, be taken seriously (or with a grain, depending on if you see the glass as half full or half empty). With that being said, my opinion is that this will not develop before the islands...this is not based on 100s of models, graphs, tables or loops. As we have all seen, science does not alays play out the way the books say it will. Call it climatology, call it instinct, call it by what is seen by the naked eye, its just MY prediction. The wave is holding its own with convection within the ITCZ/moonsoon trough but it does not have the look of anything that is "on the verge" or even attempting to get any better organized.
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Taz wasn't stating there would be no hurricanes...He just said this blog would go nuts if there was no development this season.
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Quoting Acemmett90:

kori has he been looking at the blog latly people a beoyned nuts at thsi point lol


People are always beyond nuts on here. I don't think you were around during the 2007 season, but that season invoked hell on earth on this blog. I nearly left the site because of it.

Thankfully, that year, along with 2008, taught me a lot about tropical meteorology.
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Quoting plywoodstatenative:
I think what people are discounting the information that was released earler in the year. About how the CV season will spawn up waves, but until the TUTT lifts out of the Caribbean that we will NOT see any of these waves develop. They will hit the shear in the carib and get ripped apart.

Unless they don't go into the Caribbean.
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Quoting Tazmanian:
there will be no Hurrican this year this blog will go nuts on not haveing any storms too track


Oh, there will be a hurricane, Taz. Only 1907 and 1914 saw no hurricanes.
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839. SLU
Quoting Chicklit:

So if it survived and continued at the current pace, then it would arrive in the Lesser Antilles in about a week.


well yeh .. it will bypass the northern islands over the weekend
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Quoting KoritheMan:


That image prompted me to look at an infrared satellite loop, and the circulation appears much better defined than it was just six hours ago. I think this may be designated by 11:00 PM eastern.


Yep.....I definitely think it should be TD 5-E at 11 ET....and I think it should be forecasted to become Dolores as well.
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836. SLU
Quoting hunkerdown:
There may be dry air, but it seems to be bringing its own moisture shield with it.



Well what you tend to find in that part of the Atlantic every year is that before a system develops there are usually a few strong waves which pass through ahead of it to moisten the atmosphere ahead of it to make life easier for the seedling to develop. So far this year that has not happened and the atmosphere is bone dry with abundant dust haze so this wave/monsoon trough/low will have a lot of moistening to do for it to get better conditions to develop sufficient and persistent thunderstorms especially since it is expected to move WNW to almost 20n 55w.
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there will be no Hurrican this year this blog will go nuts on not haveing any storms too track
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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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