However, other analyses show the opposite…
Correcting estimates of sea level rise
Acceleration in sea level rise far larger than initially thought
The acceleration in global sea level from the 20th century to the last two decades has been significantly larger than scientists previously thought, according to a new Harvard study.
The study, co-authored by Carling Hay, a post-doctoral fellow in the Department of Earth and Planetary Sciences (EPS), and Eric Morrow, a recent PhD graduate of EPS, shows that previous estimates of global sea-level rise from 1900-1990 had been over-estimated by as much as 30 percent. The report, however, confirms previous estimates of sea-level change since 1990, suggesting that the rate of sea-level change is increasing more quickly than previously believed. The new work is described in a January 14 paper published in Nature.
“What this paper shows is that sea-level acceleration over the past century has been greater than had been estimated by others,” Morrow said. “It’s a larger problem than we initially thought.”
“Scientists now believe that most of the world’s ice sheets and mountain glaciers are melting in response to rising temperatures.” Hay added. “Melting ice sheets cause global mean sea level to rise. Understanding this contribution is critical in a warming world.”
Previous estimates had placed sea-level rise at between 1.5 and 1.8 millimeters annually over the 20th century. Hay and Morrow, however, suggest that from 1901 until 1990, the figure was closer to 1.2 millimeters per year. But everyone agrees that global sea level has risen by about 3 millimeters annually since that time, and so the new study points to a larger acceleration in global sea level.
“Another concern with this is that many efforts to project sea-level change into the future use estimates of sea level over the time period from 1900 to 1990,” Morrow said. “If we’ve been over-estimating the sea-level change during that period, it means that these models are not calibrated appropriately, and that calls into question the accuracy of projections out to the end of the 21st century.”
To obtain their improved estimate of 20th century global sea level, Hay and Morrow approached the challenge of estimating sea-level rise from a completely new perspective.
Typically, Hay said, estimates of sea-level rise are created by dividing the world’s oceans into sub-regions, and gathering records from tide gauges – essentially yard-sticks used to measure ocean tides – from each area. Using records that contain the most complete data, researchers average them together to create estimates of sea level for each region, then average those rates together to create a global estimate.
“But these simple averages aren’t representative of a true global mean value” Hay explained. “Tide gauges are located along coasts, therefore large areas of the ocean aren’t being included in these estimates. And the records that do exist commonly have large gaps.”
“Part of the problem is related to the sparsity of these records, even along the coastlines,” Morrow said. “It wasn’t until the 1950s that there began to be more global coverage of these observations, and earlier estimates of global mean sea-level change across the 20th century were biased by that sparsity.”
“We know the sea level is changing for a variety of reasons,” Hay said. “There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present-day melting of land-ice, all of which result in unique patterns of sea-level change. These processes combine to produce the observed global mean sea-level rise.”
The new estimates developed by Hay and Morrow grew out of a separate project aimed at modeling the physics that underpin sea-level “fingerprints” – explainer from previous story.
“What we were interested in – and remain interested in – was whether we can detect the sea-level fingerprints we predicted in our computer simulations in sea-level records,” Morrow said. “Using a global set of observations, our goal has been to infer how individual ice sheets are contributing to global sea-level rise.”
The challenge, Hay said, is that doing so requires working with a “very noisy, sparse records.”
“We have to account for ice age signals, and we have to understand how ocean circulation patterns are changing and how thermal expansion is contributing to both regional patterns and the global mean,” she explained. “We try to correct for all those signals using our simulations and statistical methods, then look at what’s left and see if it fits with the patterns we expect to see from different ice sheets.”
“We are looking at all the available sea-level records and trying to say that Greenland has been melting at this rate, the Arctic at this rate, the Antarctic at this rate, etc.” she continued. “We then sum these contributions and add in the rate that the oceans are changing due to thermal expansion to estimate a rate of global mean sea-level change.”
To their surprise, Hay said, it quickly became clear that previous estimates of sea-level rise over most of the 20th century were too high.
“We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5 to 1.8 mm per year that other people had predicted,” Hay said. “But the math doesn’t work out that way. Unfortunately, our new lower rate of sea-level rise prior to 1990 means that the sea-level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought.”
###
[UPDATE] My sub-oceanic source has sent me a copy of the actual study. Here is the abstract:
Estimating and accounting for twentieth-century global mean sealevel (GMSL) rise is critical to characterizing current and future human-induced sea-level change. Several previous analyses of tide gauge records1–6—employing different methods to accommodate the spatial sparsity and temporal incompleteness of the data and to constrain the geometry of long-term sea-level change—have concluded that GMSL rose over the twentieth century at a mean rate of 1.6 to 1.9 millimetres per year. Efforts to account for this rate by summing estimates of individual contributions from glacier and ice-sheet mass loss, ocean thermal expansion, and changes in land water storage fall significantly short in the period before 19907. The failure to close the budget of GMSL during this period has led to suggestions that several contributions may have been systematically underestimated8. However, the extent to which the limitations of tide gauge analyses have affected estimates of the GMSL rate of change is unclear. Here we revisit estimates of twentieth-centuryGMSL rise using probabilistic techniques9,10 and find a rate of GMSL rise from1901 to 1990 of 1.260.2 millimetres per year (90% confidence interval). Based on individual contributions tabulated in the Fifth Assessment Report7 of the Intergovernmental Panel on Climate Change, this estimate closes the twentieth-century sea-level budget. Our analysis, which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals, also indicates that GMSL rose at a rate of 3.060.7 millimetres per year between 1993 and 2010, consistent with prior estimates from tide gauge records4. The increase in rate relative to the 1901–90 trend is accordingly larger than previously thought; this revision may affect some projections11 of future sea-level rise.
Regards to all,
w.
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The warming that’s not happening is melting ice sheets and glaciers at an increasing rate. Trenberth’s missing heat has been found! The freezing point of water must be an inverse function of atmospheric CO2 concentration. If we continue to burn fossil fuels we may freeze ourselves to death with the same mechanism we use, (with NaCl) to produce home made ice cream.
We need to spend hundreds of billions to model this. The gravy train is back on track!
Their criticism of determining global sea level using tide gauges is valid. While extremely useful regionally there are issues with the process when determining a “global sea level”. But someone probably should not throw stones who live in glass houses. Their method is worse, because it is conjecture that they built a model for, and nothing else.
Modeled conjectures is not proof or determinate of anything unless validated. Their claim that previous sea level rise was overestimated is an absurd claim. The most they can claim is they have an alternate theory and more time, work and validation is required to see if it has value. That this paper passed peer review, and Nature magazine publishes it, is troubling since it supports the odd truism of climate science: “if you can model it, it must be true”.
“We try to correct for all those signals using our simulations”
Yes, let’s throw away all those carefully recorded measurements and use our computer simulations instead.
Artificial intelligence has arrived.
From the paper:
“The KS methodology is divided into four steps, the first three of which are repeated by employing the spatial fields of GIA and ocean dynamic models from all possible combinations of 161 different Earth rheological models and 6 global climate model (GCM) simulations from CMIP5”
But they don’t just use the KS method, they use the GPR method as well!:
“the GPR approach employs Gaussian process priors for the GIA and ocean dynamics contributions that are estimated, respectively, from the 161 GIA model predictions and 6 GCM outputs”
So they have two independent methods, one using GCMs and the other using GCMs.
On ocean calamities.
Sparse records= free hand for whatever fits the purpose.
Ivy league colleges seem to be producing second-rate science these days and this one clearly followed the handbook.
Global warming dogma 101: Exaggerate current measurements, decrease past measurements, and repeat this data molestation every few years.
So stupid for warmies to keep going over this endlessly (like the temp pause), when it’s plainly obvious there’s no acceleration. Same steady, slow rate as at the end of the last glacial melt, what, last 6000 yrs?
Time to defund about 90% of these stupid “studies”.
So, when temps were increasing in the earlier part of the century sea level was rising slowly and now that temps are stationary, sea levels are rising more rapidly? I gotta tell you, even if they are right, I think that’s going to be a tough sell right across the idealogical spectrum.
It’s the eternal catch-22 of alarmism: they have to make the current temperatures unprecedented, but they also have to promise that all the DOOOOOM! is in the future, because it’s clearly not happening now.
Perhaps the least costly solution to all problems.
http://www.henrypayne.com/wp-content/uploads/2014/09/092514_UNClimateArk_COLOR.jpg
Just purchased a new ranch in near Alma Colorado…waiting for the tide to go out…pick sea shells for wind chimes…
Alma Colorado, elevation: 10,361 ft (3,158 m)
A warming ocean expands, but is pale to the likes of the pocket books for writers of catastrophic sea level science fraud publications…
Today’s Department of Water Resources California Water News picked up on the sea level rise paper:
http://www.latimes.com/science/sciencenow/la-sci-sn-climate-sea-level-20150113-story.html
and
http://www.ibtimes.com/sea-level-rise-climate-change-larger-problem-thought-new-study-claims-1783844
Re the Harvard re-study, 1991 was when the surveying datum was changed. Most of the US and territory sea level measurements were based on actual field work, the kind where you go outside and get wet and cold and hot and dirty and have to swamp out sight lines and dig around for monuments. Field work involved first-order or higher leveling by the US Coast and Geodetic Survey, the precursor agency to NOAA. Most of last century’s measurements were based on the National Geodetic Vertical Datum of 1929 (NGVD 29), based on physical benchmarks at the coasts. Quoting NOAA FAQ:
“Mean sea level was held fixed at the sites of 26 tide gauges, 21 in the United States and 5 in Canada. The datum is defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment. A total of 106,724 kilometers of leveling was involved, constituting 246 closed circuits and 25 circuits at sea level.”
The datum was changed in 1991 based on the Earth’s geoidal (equipotential) surface. Again quoting NOAA FAQ:
“The North American Vertical Datum of 1988 (NAVD 88) is the vertical control datum established in 1991 by the minimum-constraint adjustment of the Canadian-Mexican-United States leveling observations. It held fixed the height of the primary tidal bench mark, referenced to the new International Great Lakes Datum of 1985 local mean sea level height value, at Father Point/Rimouski, Quebec, Canada. Additional tidal bench mark elevations were not used due to the demonstrated variations in sea surface topography, i.e., the fact that mean sea level is not the same equipotential surface at all tidal bench marks.”
There is not a simple 1:1 relationship between old elevations tabled in NGVD 29 vs. NAVD 88. The difference in some locations can be about a meter. NOAA provides a conversion tool at:
http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html
It appears that the researchers did not look into the above details when casting aspersions on the work of the surveyors of the last century. The primary purpose of the coastal surveying was for coastal engineering works related to harbors and dredging. What the “sea level” might have been out in the middle of the ocean wasn’t on anyone’s radar back then, because ships don’t dock out there and the water is deep enough to not require dredging.
On the subject of dredging, has the alleged unprecedented acceleration in sea level been reflected in a corresponding decrease in dredging contracts let by harbor and port authorities?
Dredging has zero affect on tide levels. Dredging has been partially slowed by ecology “experts” who have engaged in not disturbing nature (or our pollution). Example: It was okay to divert the Nooksack river into Bellingham Bay which has been filling up with river sediment from the river, but do not dredge out the muck filling in the bay. Why? Several reasons…one of which, the new mud is burying the “stuff” Georgia Pacific was dumping into the bay. Similarly, one could assume dredging of other water ways can be stopped by ecology groups for reasons of similar concern. However, there was not much concern when the pollution was being dumped…hmmmm. A bit off topic, but…what it is…is. Cheers
Bellingham-Washington-vacation-rental-home-proID-59112.html
…my driveway. 🙂 living well under water. blub blub….blub….
Has anyone posted these?
Jevrejeva, et al., reported that “the new reconstruction suggests a linear trend of 1.9 ± 0.3 mm/yr [7.5 inches per century] during the 20th century” and “1.8 ± 0.5 mm/yr [7 inches per century] for the period 1870 to 2008.” http://kaares.ulapland.fi/home/hkunta/jmoore/pdfs/Jevrejevaetal2013GPChange.pdf
Cazenave, et al., reported that gravitational-recovery satellites showed sea level falling or stable from 2003-2009, “The rate of sea-level rise,” Cazenave, et al., v. 4, Nature Climate Change, pp. 358-361, 4 Feb. 2014.
Why are the most recent 3 years missing from this analysis?
As a petrophysicist, I work with data recorded by electronic instruments within well bores, and try to draw conclusions about the underground formations. I always want to start with the “raw” data, that is the data that have not been adjusted or “corrected”. Granted, sometimes corrections to the recorded data are necessary, but the uncorrected data must always be available for others to reference. I have read the post, and it appears that the authors are further manipulating already manipulated data. Furthermore, I cannot tell whether they are basing their conclusions on the manipulated observations, or predictions based on what they believe are the rates of ice melts and thermal expansion. Either way, their conclusions are many steps removed from reality.
I believe in direct observation. I recently visited an island resort in Fiji. On the wall in the bar (one of my favorate places on the island), was an airial photograph of the island when the owner purchased it in 1976. Below that photo was another from 2006. I studied the two photographs carefully to see if there was any evidence of sea level rise. I couldn’t see any significant changes in the shore line (but if I could get a big enough government grant, I would go back and study the matter more thoroughly).
Another observation I have made, is that Hollywood celebrities, who are so terribly concerned about climate change, continue to pay millions for ocean front property.
Wonderful! I’ll have beachfront property in San Antonio in almost 550,000 years!