NOTE:
Three good articles combined into one. The SUMMARY and CONCLUSION sections were moved from the end to the beginning of each article, with no edits. The DETAILS are a shortened edited version, especially reducing the IPCC Report quotes. Mr. May's quotes are far more accurate than the usual IPCC scaremongering. If you prefer the full versions of all three articles, visit the author's blog at: https://andymaypetrophysicist.com/climate-blog/
You might want to bookmark the URL -- It's a good climate science blog.
Ye Editor
Source of Part 1:
https://wattsupwiththat.com/2022/03/19/ar6-and-sea-level-rise-part-1/
"AR6 (IPCC, 2021) 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?
SUMMARY:
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.
DETAILS:
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.” 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) ... On page 9-8 (Chapter 9, page 8) of the AR6 report:
... 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: https://elonionbloggle.blogspot.com/2022/03/phony-proxy-rates-of-sea-level-rise-by.html
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.
... 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.
.... 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 ...
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?
... ocean warming since the Little Ice Age, provides about half of sea level rise.
Melting ice provides most of the rest.
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."
The bibliography can be downloaded here:
https://andymaypetrophysicist.com/wp-content/uploads/2022/03/AR6-and-sea-level-Bibliography_1.pdf
"SUMMARY:
The statistical methods used in AR6 to show sea level rise acceleration were quite crude, as discussed in Part 1.
They simply cherry-picked data and used least squares fits of them to estimate acceleration.
In this part we show that the error in estimating sea level rise and its components is so large that showing acceleration definitively is probably not possible.
In Part 3 we will discuss the problems with that approach and provide a more statistically sound projection of the rate of sea level rise.
DETAILS:
Thomas Frederikse and colleagues published a study of sea level data, considering both tide gauges and satellite data in 2020 (Frederikse, et al., 2020).
This paper is frequently cited in the Chapter 9 AR6 sea level discussion.
They found that there are many causes of global and regional sea level change that need to be considered.
Land over much of the Northern Hemisphere is still rebounding from the melting of the massive glaciers they supported during the Last Glacial Maximum.
This causes many northern tide gauges to record sea level falling as the land rises.
Further, dam construction during the twentieth century caused water to be withheld from the oceans and stored in reservoirs on land, especially between 1960 and 1980.
They also tell us that previous assessments of sea level were unable to reconcile observations with the calculated contributions of ice-mass loss, dam construction, and thermal expansion of water.
As mentioned in Part 1 of this series, observed sea level change is very small, so this is not surprising.
Yearly changes are below the measurement accuracy of the instruments.
The observations of sea level, ocean temperature, ice-mass loss, water held in man-made reservoirs, and total river discharge to the oceans all have considerable uncertainty,
which is why studies have not been able to close the gap between observations.
Frederikse and colleagues make another attempt to close the gap.
They note that over the past few years much more accurate estimates of all the critical observations have been made available and they collected these in a new estimate.
Their best estimate of the observed sea-level rise trend from 1900 to 2018 is 1.56 ±0.33 mm/year, an error of ±20%.
... The observed sea level uncertainty, prior to 1990, generally exceeds ±10 mm;
prior to 1960, it exceeds ±15 mm.
Prior to 1940, it exceeds ±20 mm.
The sub-components of barystatic changes examined in the paper are: glacier melting, melting of the Greenland and Antarctic Ice Sheets, and terrestrial water storage (including new dam construction and groundwater depletion).
Thermosteric changes are estimated using ocean subsurface temperature measurements.
Frederikse, et al. try to reconcile the component total with observed sea level changes as measured by satellite
and tide gauges using a model and find modest agreement, within the respective margins of error.
The results of his study increase the previous estimates of GMSL (global mean sea level) rise in the 1960s and 1970s, after excluding the effect of dam construction.
His model also increases the uncertainty prior to 1940.
The match is quite poor in the 1920s and 1930s, and the steep rise in sea level from 1930 to 1950, nearly as rapid as in the 21st century, is also not matched well.
The periods where the match between the observations ... do not match are particularly poor from 1915 to 1950.
The rapid slowing of the rate of rise between 1950 and 1965 is not matched well at all.
The rapid rise from 1990 to 2005 is only marginally better than the other periods.
... it seems possible that the apparent acceleration in sea level rise from the late-1980s to about 2005 was merely a repeat of the acceleration from about 1925 to the early 1940s.
Even if this is not true, it is clear that the data are not accurate enough to conclude that the overall rate of sea level rise is accelerating,
in fact it is possible that we will see a deceleration of sea level rise in the near future."
The bibliography can be downloaded here:
https://andymaypetrophysicist.com/wp-content/uploads/2022/03/Post-2-bibliography.pdf
(Wyatt & Curry, Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century, 2014) and (Wyatt, The “Stadium Wave”, 2014)
"CONCLUSION:
In the United States we would call the AR6 attempt to convince us that the rate of GMSL rise is accelerating, using adjoining cherry-picked least squares lines “high school,” meaning unsophisticated.
Their method is problematic because GMSL is heavily autocorrelated and non-stationary, rendering their cherry-picked least squares fits and least squares statistics invalid.
Our fit, using the R function arima, is at least statistically valid.
We specifically corrected for autocorrelation and forced the series to be stationary.
We also addressed the minor partial autocorrelation that was left at one quarter and three quarters.
The residuals of our model passed both the overall Ljung-Box test and multiple-lag Ljung-Box tests for white noise, meaning the arima model properly captured the 140-year trend in the NOAA sea level data.
Thus, while AR6 cherry-picked periods to support their conclusion that GMSL is accelerating, we reached the opposite conclusion using all the data in a statistically valid way.
This does not mean that our forecast is correct, but it does mean that the AR6 speculation that sea level might rise 5 meters by 2150 is extremely unlikely and is best characterized as irresponsible speculation.
Our analysis found no statistical evidence of acceleration and produced a linear extrapolation.
While warming of Earth’s surface is clearly the reason land-based glaciers are melting, which does contribute to rising sea level, AR6 provides no evidence the warming is caused by human activities.
They use models to infer humans caused it, but unfortunately their models are also not statistically valid as shown in Part 2, and by McKitrick and Christy (McKitrick & Christy, 2018).
We can all agree that humans probably have some impact on atmospheric warming, but we do not know how much is caused by humans and how much is natural,
because we are emerging from the unusually cold Little Ice Age—the “preindustrial” period.
Further, as we saw in Part 2, the 30-year rates of sea level rise reveal a distinctly natural-looking oscillation.
Glacial ice and ice sheet melting is likely responsible for most of sea level rise, as AR6 states, but the human fraction of that warming might be quite small.
Thus, from a purely statistical point of view, the AR6 claims are childishly invalid.
A proper analysis of the data leads to a forecast of roughly 20 cm (~8 inches) of sea level rise by 2100. In the year 2100, our descendants will know who was right.
DETAILS:
In Part 1 of this series, we examined the data and analysis that was presented in AR6 to support their conclusion that sea level rise is accelerating.
In Part 2 we looked at a serious examination of the observational record for sea level rise over the past 120 years and the modeled components of that rise.
We concluded in Part 1 that the statistical evidence presented in AR6 for acceleration was crude and cherry-picked.
In Part 2 we saw that the error in both the estimates of sea level rise and in estimating the components of that rise is very large.
The error precluded determining acceleration with any confidence, but the data revealed an approximately 60-year oscillation of the rate of sea level rise that matches known natural ocean cycles.
Modern statistical tools allow us to forecast time series, like GMSL (global mean sea level) change, in a more valid and sophisticated way than simply comparing cherry-picked least squares fits as the IPCC does in AR6.
Our forecast is based on pure statistics.
It is done in the correct way, but is not necessarily correct, statistics are like that.
We will not know for sure until 2100.
... The forecast we created predicts that GMSL will rise between 148 (6 inches) and 258 mm (10 inches) by 2100.
Many researchers call this alarming, but humans have successfully adapted to much higher rates of sea level rise in the past ... without the technology we have today.
When we consider that the average open ocean daily tide range is 1,000 mm or three feet, eight inches of sea level rise over 100 years does not seem like much.
In the 20th century sea level rose 5.5 inches, did anyone notice or care, aside from a few researchers?
The forecast with more detail: The model predicts mean sea level in 2100 of 203 mm over the 1993-2008 average.
The 95% confidence limits are 148 (6 inches) to 258 mm (10 inches) and marked with a curly brace.
The range of predictions is not alarming, it is just over the 140 mm or 5.5 inches observed in the 20th century ...
Reference:
McKitrick, R., & Christy, J. (2018, July 6). A Test of the Tropical 200- to 300-hPa Warming Rate in Climate Models, Earth and Space Science. Earth and Space Science, 5(9), 529-536. Retrieved from https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018EA000401