By Andy May
This is the first of a three-part series on the IPCC’s discussion of sea level rise in their latest report, AR6 (IPCC, 2021). The report claims that the rate of sea level rise is accelerating. It is fair to ask why they think this, what evidence do they offer?
We find the following in the AR6 Summary for Policymakers:
“Global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018. The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr–1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr–1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr–1 between 2006 and 2018 (high confidence). Human influence was very likely the main driver of these increases since at least 1971.” [Bold added]
AR6 Summary for Policymakers, page SPM-6 (IPCC, 2021)
And the following in AR6, Chapter 9:
“Global mean sea level (GMSL) rose faster in the 20th century than in any prior century over the last three millennia (high confidence), with a 0.20 [0.15–0.25] m rise over the period 1901 to 2018 (high confidence). GMSL rise has accelerated since the late 1960s, with an average rate of 2.3 [1.6–3.1] mm yr-1 over the period 1971–2018 increasing to 3.7 [3.2–4.2] mm yr-1 over the period 2006–2018 (high confidence). New observation-based estimates published since SROCC [Special Report on the Ocean and Cryosphere in a Changing Climate, 2019] lead to an assessed sea level rise over the period 1901 to 2018 that is consistent with the sum of individual components. While ocean thermal expansion (38%) and mass loss from glaciers (41%) dominate the total change from 1901 to 2018, ice sheet mass loss has increased and accounts for about 35% of the sea level increase during the period 2006–2018 (high confidence).”
On page 9-8 (Chapter 9, page 8) of the AR6 report:
And, farther in Chapter 9:
“At the basin scale, sea levels rose fastest in the Western Pacific and slowest in the Eastern Pacific over the period 1993–2018 (medium confidence). …The anthropogenic signal in regional sea level change will emerge in most regions by 2100 (medium confidence).” [bold added]
AR6 Chapter 9, page 8.
It is a little distressing that in the Summary for Policy Makers (SPM) they conclude that human influence was “very likely” the main driver of the acceleration in sea level and in Chapter 9 they admit they do not expect to observe an anthropogenic signal in regional sea level change before 2100.
Global Mean Sea Level (GMSL) might have increased more in the 20th century than at any time in the past 3,000 years, but how would anyone know? There were no tide gauges or satellites 3,000 years ago. Neither tide gauges nor satellites are accurate at the millimeter level, and certainly historical records and geological proxies from three thousand years ago are not. The geological proxies of past sea level are explained by Willis Eschenbach here. Warning, if you have a sensitive stomach, don’t look at Willis’s plots!
Further, why should this mean anything? Glaciers advanced to their lowest Holocene elevations during the Little Ice Age from 1600 to 1850, swallowing entire villages in the process (Behringer, 2010, pp. 89-90). The Little Ice Age was the coldest period in the entire Holocene—roughly 11,700 years ago to the present day. As Little Ice Age glaciers melt, one would expect sea level to rise a little, but just how significant is this? More importantly can we be confident the rate of GMSL rise is accelerating?
We also find it strange that they conclude the rate of GMSL rise is increasing based on comparing linear least squares fits to selected portions of the sea level record. Figure 1 plots the entire NOAA GMSL record by quarter since April 1880. The x axis is the number of quarters (three-month periods), and mean sea level is given on the y axis through 2020. This record is built from the Church and White (Church & White, 2011) GMSL data to 2010 and University of Hawaii Fast Delivery data after that.
AR6 selects numerous specific intervals in the quotes above to justify their claim that the rate of sea level rise is accelerating. This claim is visually dubious since the data look a bit wavy, but linear. The period of apparent acceleration from 180 to 300 (1925-1952), looks suspiciously like 420 to 510 (1985-2007). The entire record, from April 1880 to the end of 2020 has a slope of 1.65 mm/year with an R2 of 0.97. We could cherry pick periods all day and not resolve anything significant regarding acceleration or the lack of it. The least squares statistics for the AR6 cherry-picked periods mentioned in the quotes above are given in Table 1 and compared to four I cherry-picked.
While AR6 claims acceleration is occurring with high confidence, the previous report states:
“The trend in GMSL observed since 1993, however, is not significantly larger than the estimate of 18-year trends in previous decades (e.g., 1920–1950).”
AR5: (IPCC, 2013, p. 290)
One wonders why AR6 has a different view only seven years later.
AR6 would have us believe that because a least squares linear fit to the rise in sea level is larger from 2006 to 2018 than from 1971 to 2018 it is accelerating. Yet from 2012 to 2020 the rate is nearly as low as from 1971 to 2018. The largest rate of rise in Table 1 is only 15 inches or 38 cm per century, hardly alarming when global tides, in the open ocean, average more than twice that; and coastal tides are often ten times that value daily. Climate changes on a temporal scale of centuries, as we can see comparing the Little Ice Age to the Medieval Warm Period, so an instrumental record from 1880 to 2020 is unlikely to capture the full range of sea level rates. Estimates of sea level rise gathered from historical and geological records show that sea level has risen much faster in the past, as shown in Figure 2 created by Robert Rohde.
Sea level is estimated using tide gauges mounted on coasts around the world. The very best of these gauges are only accurate to ±5 mm for a monthly average (NOAA, 2020). Satellite measurements of sea level are problematic unless meteorological conditions are perfect, and they are trying to measure the altitude of a moving surface. AR6 admits that satellite estimates of sea level rise “acceleration” are much smaller than the heavily massaged tide gauge records. This is discussed on page AR6 page 9-96, where we see that satellites find acceleration from 1993 to 2015 to 2006-2015 is from a rate of 3.16 mm/year to 3.58 mm/year, this is an acceleration of less than half a mm/year2 in roughly a decade. Other satellite estimates are similar. Satellite estimates of sea level are not accurate to one-half of a millimeter (Frederikse, et al., 2020).
Is the difference between an estimated global average rate of 3.8 mm/year and 1.8 mm/year statistically significant, considering the data used? Particularly when these measurements are made over a few decades? It seems unlikely, but let’s look at the data more closely.
The AR6 statements suggest that the rate of sea level rise is increasing due to human influence. This is presumably due to greenhouse gas (GHG) emissions causing surface warming, which then melts glaciers sitting on land. This raises two questions:
- Is the increase in the rate of sea level rise statistically significant?
- If so, could warming due to human GHG emissions have caused it?
From AR6:
“Heating of the climate system has caused global mean sea level rise through ice loss on land and thermal expansion from ocean warming. Thermal expansion explained 50% of sea level rise during 1971– 2018, while ice loss from glaciers contributed 22%, ice sheets 20%, and changes in land water storage 8%. The rate of ice sheet loss increased by a factor of four between 1992–1999 and 2010–2019. Together, ice sheet and glacier mass loss were the dominant contributors to global mean sea level rise during 2006-2018 (high confidence).”
AR6 page: SPM-14
Thus, ocean warming since the Little Ice Age, provides about half of sea level rise. Melting ice provides most of the rest.
From AR6:
“By 2100, GMSL is projected to rise by 0.28–0.55 m (likely range) under SSP1-1.9 and 0.63–1.02 m (likely range) under SSP5-8.5 relative to the 1995–2014 average (medium confidence). Under the higher CO2 emissions scenarios, there is deep uncertainty in sea level projections for 2100 and beyond associated with the ice-sheet responses to warming. In a low-likelihood, high-impact storyline and a high CO2 emissions scenario, ice-sheet processes characterized by deep uncertainty could drive GMSL rise up to about 5 m by 2150. Given the long-term commitment, uncertainty in the timing of reaching different GMSL rise levels is an important consideration for adaptation “
AR6 page TS-44
Some IPCC climate models predict up to 5 meters of sea level rise by 2150, when the current rate of sea level rise is less than 40 cm or 1.3 feet per century? Considering that the IPCC models have not predicted climate accurately after 30 years of trying (McKitrick & Christy, 2018), pardon my skepticism.
AR6:
“It is virtually certain that global mean sea level will continue to rise through 2100 …
Beyond 2100, GMSL will continue to rise for centuries due to continuing deep ocean heat uptake and mass loss of the Greenland and Antarctic Ice Sheets and will remain elevated for thousands of years (high confidence).”
AR6 Chapter 9, page 9-9.
The first statement is likely true, we are still warming as we come out of the Little Ice Age and I would doubt a change in direction of glacier retreat before 2100, the second statement is pure speculation, projecting beyond 2100 is reckless.
In summary, the AR6 statements about acceleration of sea level rise are based on simple cherry-picked and crude linear least squares fits to sea level data for the past 140 years. They also incorporate data and trends of ocean warming and land-based glacier melting. The problem is the rate of rise of sea level is so small today and so linear that their attempts to predict large rates of sea level rise are statistically inept and almost comical. In the next post we examine the complexity of measuring GMSL, and later in this series we will provide a more statistically significant projection of sea level rise that is much less than the wild predictions from AR6.
The bibliography can be downloaded here.
The long term line looks quite flat in trend. If they want to try to find a hockey stick there, it will take fancier math tricks than Mann’s.
Looks like a typical bunch of IPCC fear-mongering garbage.
As posted here before, both Church and White and NASA satellites are suspect.
The Church and white methodology uses a large selection of tide gauges assuming vertical land motion cancels out. It demonstrably doesn’t.
The NASA data purports to be less than 1mm precision, when the tech spec for Jason 3 and now Sentinal-6 say a few centimeters. See post Jason 3 fit for purpose? And two on Sentinal-6 for details.
there are about 65 long record (>60 years) tide gauges close to a diffGPS to correct for vertical land motion. They say about 2.2mm/year and no acceleration. And, they all agree to within a mm by continent plus Japan, so not an artifact of ocean currents. Moreover, 2.2mm/year closes exactly with the sum of satellite estimated ice sheet loss and ARGO estimated thermosteric rise. Details in guest post ‘SLR, acceleration, and closure’. This number also proves the land motion deficiency in Church and White methodology.
They do mention that sea level rise includes a rise in sea level due to thermal expansion, but then they cherry pick the period ending in 2018 which includes a recent strong El Nino. They also leave out the glacial isostatic adjustment added each year since about 2010.
14,000 years for the last 100 meters. At current maximum calculated rates 39,000 years for the next 100 meters. Some acceleration. (Check my math.)
There was a nice article a little while ago about Antarctica creating cold brine and injecting that into the southern ocean where it enters the bottom circulation stream which takes 800 years to complete. So I guess we could project a colder ocean sometime in the future. Since the Antarctic has been cooling for the past 60 years it will take a little time to show up.
While I am certain that the oceans have warmed over the past 140 years, we do not have enough coverage know to get an accurate reading of the oceans temperature now and we certainly didn’t in 1880. So to try an make an accurate guess in millimeters about how it much affects global sea level rise would need wide error bars.
“The first statement is likely true, we are still warming as we come out of the Little Ice Age and I would doubt a change in direction of glacier retreat before 2100, the second statement is pure speculation, projecting beyond 2100 is reckless.”
We already have photographic evidence and written testimonials about glaciers retreating and advancing just in the past 140 years, so I would have no confidence in saying that glaciers can not change back to advancing again.
As I explained, a lot of that sea-level-acceleration stuff compares apples to oranges.
Andy, I think that should really say “… until about 7,000 years ago.”
Greenhouse factor appears to be a constant 1/3 from a LW radiation perspective.
1 – (TOA / Surface). We have approximate data to show this empirically. The ratio of TOA and surface temperature remains unchanged.
Those who get lost in reducing the question to L↑ and L↓ will never understand the nature of climate change.
Any increase to temperature results in an increase to both upwelling and downwelling IR.
Surface temperature is a consequence of net solar input warming and the net sensible and latent heat flux away from surface.
In the case of ocean, surface temperature also relates to variable internal oceanic circulations which have yet to be adequately characterized.
The efficiency of heat flux away from the surface is a function of surface heat capacity, moisture availability, surface pressure or density, turbulence, and the availability of condensation and precipitation nuclei.
Change any of those, change climate. Average up all the climates, and you get some notion of ‘global climate change’. Eventually, any average change to climate is projected to poles on global circulation.
Greenhouse factor x Surface Temperature = Greenhouse Effect.
Any change to surface temperature will appear to result in a change to Greenhouse Effect when viewed from a LW perspective.
However, the effect of the atmosphere, or greenhouse Factor, remains unchanged. This, despite an apparent change to greenhouse Effect.
0.3 x Ta = GEa
0.3 x Tb = GEb
Thus, moving forward, to understand climate we must understand surface energy budget.
Surface energy budget is composed of a variety of microclimates ranging from land deserts to rainforests, to various ocean surfaces with dynamic heat delivery mechanisms. Variable radiation input, variable heat flux.
Some argue if you completely plug up the IR window, such as on a humid day, you get an additional 5 W m-2 LW budget.
What causes an increase to humidity? Certainly not CO2. Humidity is a function of available precipitation nuclei all else being equal. Reduce precipitation nuclei, increase humidity.
Over ocean, the primary precipitation nuclei is limitless hygroscopic salt aerosol. For frontal systems it is ice. Over the continents it is microbes or hygroscopic bacteria. Reduce continental biota, say forest cover, increase humidity over land. Now, 40% of the land has been cleared. The consequence is increasing high pressure domes over the continents.
The point being, a water vapour feedback is independent of CO2. This critically important point has been misunderstood. Considering the greenhouse Factor is constant, an increase in humidity over continents eventually rains out over ocean. .
The ongoing incredulous mischaracterization of climate and gross negligence of relevant factors has led to fallacious policy choices.
“Thermal expansion explained 50% of sea level rise during 1971– 2018..”
Thermal expansion is effectively ZERO at the coastline. There is simply not enough depth if water to make thermal expansion significant. Throwing the term ‘Thermal Expansion’ into a report is just another example of the IPCC talking scientific nonsense!
A 1 degree C temperature of the water (not the atmosphere) will give at most a 1% increase in volume (vertical, not lateral) of the top 100-200 metres of the central ocean. Coastal water depth will be measured in feet or inches and a 1% increase of less than 100mm of water temperature is less than 1 mm. So far the measured sea water temperature increase is way less than 1 degrees C, so any coastal rise is negligible, as attested by PSMSL measurements.
The IPCC reports are pure advocacy with little or no basis in science
Andy May, wee typo….
“This is discussed on
pageAR6 page 9-96, where we see that satellites find acceleration from…..”This is confusing !
“where we see that satellites find acceleration from 1993 to 2015 to 2006-2015 is from a rate of 3.16 mm/year to 3.58 mm/year” ?
Great post !
Good first report, Andy, I’m waiting for the other two. I think us geologists think sea level is a reasonable indicator of what state, especially liquid or solid, H2O is trending into. However, us geologists also think in terms of “Dynamic Earth”, wherein the oceans are not fixed water containers, but rather quite dynamic. For instance, Continental Drift/Plate Tectonics modifies the basin volume, undersea volcanism also, then those pesky rain/river/erosion gremlins try to fill up the basin (at rates from 1 meter per year near river mouths to 0.1 cm per thousand years in the open ocean where only wind-blown material settles), then the seawater expands because heat of undersea volcanism heats it up, then (see Canary Island Volcano) a land-based volcano pours lava into the basin, then those human rascals blow up an island to test a hydrogen bomb, etc, etc. Here is a clue about where to buy a house: the east coast of the Americas is going down and the west side is going up (never mind the volcanos and earthquakes).
Andy
Thank you for this fine article, especially this “The anthropogenic signal in regional sea level change will emerge in most regions by 2100 (medium confidence)”
I read Chapter 9 more than once and missed that sentence each time. It’s a critical point and something that some authors have stated in their own papers.
There are so many uncertainties about the rates of rise and acceleration amounts that they should be embarrassed by stating anything with confidence.
I have ordered new reading glasses.
“Thus, ocean warming since the Little Ice Age, provides about half of sea level rise. Melting ice provides most of the rest.”
And, given the response time lag from warming, how much of the present day melting of ice is simply in response to us coming out of the LIA 100+ years ago…and this is your “existential threat”…
If Sea Level rise wasn’t “accelerating” because of global warming, it would just be “decelerating” also due to global warming, due to having melted most of the temperate zone mountain glaciers….this is not worth discussing with warmunists. The fact that SL is increasing only means that someday it will decrease again, as records show it did at the end of the Little Ice Age before the present surface warming started. In fact, this SL reversal is why 1860-ish is generally considered to be the end of the LIA along with community records in the Alps showing glacier advances stopped.
Graphs showing late LIA decrease recently published at WUWT by David Middleton here.
https://wattsupwiththat.com/2021/08/10/eemian-sea-level-adjusted-downwards/
A few days ago I got beat up for reporting that long term PSMSL tide gauges averaged out to 0.01 mm/yr² of acceleration over the last 100 years. Well I looked at the distribution of those 73 stations, and about 28% were less than that. So I have to agree that noise, numbers and statistics says that you really can’t say that just because the mode was 32% 0.01 mm/yr² that it was significant.
Usually acceleration is expressed as units of distance per units of time squared. There was only one instance of that in the above article:
“This is discussed on page AR6 page 9-96, where we see that satellites find acceleration from 1993 to 2015 to 2006-2015 is from a rate of 3.16 mm/year to 3.58 mm/year, this is an acceleration of less than half a mm/year2 in roughly a decade.”
Maybe later I’ll look that their comparison of this and that linear rate from this and that time period to see what the good ol’ (v2-v1)/t=a formula I learned in high school says (-:
No mention of the Colorado Sea Level Research Group C-SLRG and their insane claim of 0.098 ± 0.025 mm/yr² acceleration of sea level rise since 1992. I mean, really? They couldn’t round it off to 0.1 mm/yr².
The bottom line in science is outcomes. REAL science makes accurate predictions. If this science is sound, an accurate prediction can be made. Pseudoscience sounds scientific, but it consistently fails with its predictions. The so-called “science” is deliberately confusing-lay people just give up-“whatever” and just accept “whatever” because those using the confusing language and terms “must know what they are talking about.”
Once people, knowing they are no experts in the field succumb to the “whatever” of just accepting the word of “experts” as gospel truth, the deception has been successful.
Almost everyone would be totally confused reading the actual report, so they will naturally gravitate directly to the summary for policymakers, especially politicians who would not have time to read the entire report anyway. “Whatever” is then blind acceptance of the politically motivated “conclusion” the summary tells them to believe and act upon. It trades on the perceived respectability of the report. This is the classic tactic of con men. They pump their own tyres to appear respectable, hiding their true intent (to deprive you of your money.) In the case of the parent body of the IPCC, it is deprive all of us of our money, access to reliable energy and ultimately deprive us of our freedom. They are not going to say this upfront, although admissions come out, which fly right over the heads of many. Example- Klaus Schwab , head of the WEF -“You will own nothing and you will be happy.” It is openly admitted, but this just flies over our heads.
Looks like the “conspiracy theorists” have some serious issues that must be investigated. If even ONE of the “conspiracy theories” turns out to be valid, then the “conspiracy theorists” cannot be just dismissed out of hand. Having said all that, there are some absurd conspiracy theories put out there that are clearly there to put “conspiracy theorists” in to disrepute. The classic one is flat earth theory, which is easy to disprove, but nutters (and perhaps saboteurs as well) come out with absurd excuses to cite as “evidence.” This then affects the credibility of all people who are on the scent of actual conspiracies.
Well, since sea level is not rising catastrophically, or even perceptively, this is yet another pile of lies spewed by the usual lie spewing liars.
Andy, nice part one of three. Looking forward to the other two installments.
Your exposee of the contradictions between AR6 SPM and WH1 chapter nine is surprising to me, because SLR acceleration is one of easy IPCC basic flaws that skeptics look to.
Others include:
— Arctic summer sea ice gone by now
— Polar bears endangered
— Climate refugees
— Climate models getting better
All are easily verified as fundamentally failed predictions. Yet they double down each AR, making ridicule easier with each one.
I just check The Battery sea level gauge in New York City from time to time. So far, it’s a straight non-accelerating increase and has been so since before Lincoln was President. And half of the reported rise is due to land sinking as shown by the nearby GPS elevation gauge. When it starts to accelerate, I will start believing sea level rise is accelerating.
Dead On Arrival.
“By 2100, GMSL is projected to rise by 0.28–0.55 m (likely range) under SSP1-1.9 and 0.63–1.02 m (likely range) under SSP5-8.5 relative to the 1995–2014 average (medium confidence).”
We look at the first claim, the smallest SLR given.
0.28 meters = 11.0 inches in 80 years = 13.8 inches / century.
This is *fully double* the generally accepted value of GMSLR of ~6. inches / century.
The number is a modeled result and is utterly unsupportable given the huge set of tide gauge data.
Dead, Dead, Dead.
It’s dead, Jim.
Dammit Jim, I am a Climate Scientist, not a Starfleet doctor.
The graph is clearly accelerating.
Sorry for that
Andy, why do you discuss such BS? A report produced by the totally corrupt UN?
CODE RED?
GHE, ECS. SLR?
There is no evidence for any for them. In fact, I would put this in the realm of unicorns and angels dancing on the head of a pin.
Is this your main stream of income?
WUWT deserves better.
We were warned that the Maldives were on the verge of going under water. I just read they’re building five new airports to handle the booming tourism trade. Must be a lot of scuba divers heading there.