Epistemic uncertainty in the kinematics of global mean sea-level rise since 1993 and its dire consequences

ABSTRACTRecent studies reported an ambiguous global sea level acceleration during the satellite altimetry (SA) era (1993–2017). New SA data created an opportunity to resolve this issue. In this study, two competing kinematic models to represent global mean sea level anomalies are compared. The first model consists of an initial velocity and uniform acceleration. The second model replaces the initial velocity and acceleration with a trend and a representation of a long periodic lunar subharmonic of period 55.8 y, which is determined to be statistically significant at globally distributed tide gauge records. The models also include parameters for the periodic effects of lunisolar origin with periods 18.6 y and 11.1 y annual, and biannual variations in 10-day average of globally SA measurements during 1993–2022. Generalized least squares solutions yielded updated statistically significant estimates for all the model parameters and their statistics for both models. However, the outcome failed to resolve the ambiguity of uniform acceleration in global mean sea level confounded with the long periodic lunar subharmonic of period 55.8 y during this period. This epistemic uncertainty will have a dire impact on climate change risk assessments as demonstrated through the prospective comparison of both kinematic models

Sub and superharmonics of the lunar nodal tides and the solar radiative forcing in global sea level changes

The working hypothesis of this study is that periodic lunar nodal tides and almost periodic solar radiation variations influence sea level changes through their harmonic beating of nearby natural and/or forced broadband oscillations of the sea level at multi-decadal frequencies. The presence of the harmonics of the lunar nodal tides and the solar radiation variations, including the pole tides, is investigated by modeling and estimating the amplitudes of the corresponding periodicities in 27 globally distributed long tide gauge records. Statistically significant signatures of sub and superharmonics of lunar nodal tides and forced sea level variations due to solar radiation are detected in all station records.Meta-analysis of the harmonic amplitudes from all stations reveals that the effect sizes are statistically significant and provide evidence for the harmonic beating of sea level changes as a global phenomenon. Consequently, the compounding of the lunar nodal tides and forced sea level changes due to solar radiation with other broadband natural and forced sea level oscillations is a plausible explanation for the recent sea level accelerations and decelerations detected by satellite altimetry measurements and long tidal records

Acceleration of the global coastal sea level rise during the 20th century re-evaluated

In contrast to some of the recent investigations, this study shows that far less number of tide gauge stations experienced statistically significant accelerations in sea level rise during the 20th century. Twenty-seven tide gauge stations with century long data were analyzed for the presence of an acceleration in global sea level rise using a kinematic model inclusive of a secular trend, acceleration, and compounded periodicities with autocorrelated random effects. Eight out of twenty-seven stations revealed statistically significant but slow sea level rise acceleration (p<0.01) within the 0.01-0.02 mm/yr2 range compared to the sixteen stations with accelerations estimated using the models by the previous investigations,which did not account for the compounded periodicities and autocorrelations in sea level changes

Why and how to predict sea level changes at a tide gauge station with prediction intervals

Predicting sea level rise is essential for current climate discussions. Empirical models put in use to monitor and analyze sea level variations observed at globally distributed tide gauge stations during the last decade can provide reliable predictions with high resolution. Meanwhile, prediction intervals, an alternative to confidence intervals, are to be recognized and deployed in sea level studies. Predictions together with their prediction intervals, as demonstrated in this study, can quantify the uncertainty of a single future observation from a population, instead of the uncertainty of a conceivable average sea level namely a confidence interval, and it is thereby, better suited for coastal risk assessment to guide policy development for mitigation and adaptation responses

The first sexaxial figure of the Earth

ABSTRACTIn this study, a sexaxial figure of the Earth was created using randomly distributed 6400 control points on the geoid, which was generated by the EGM2008 gravity model. The shape of the sexaxial ellipsoid is defined by its six orthogonal axes. To construct the new geometric figure, eight triaxial ellipsoids were fitted to the Cartesian coordinates of control points in each octant of the geoid using the least squares method. Its geometric origin is constrained to coincide with the centre of mass of the geoid, and the ellipsoid has no net rotation with respect to the WGS84 coordinate system. This study demonstrates that the new geometric figure provides a customised fit to the control points in each octant

Is the global sea surface temperature rise accelerating?

This is an exploratory investigation to search for the presence of an acceleration in global sea surface temperature rise, which is essential to identify anthropogenic contributions to the climate change during the 20th century. A weighted statistical model with an acceleration parameter was built progressively to reconstruct the variations in the global sea surface temperature data considering statistically significant confounders and autoregressive disturbances in the process. From the preliminary residual analysis of a weighted regression model, emerged a parsimonious model with first order autoregressive disturbances with a deterministic trend, acceleration and periodicity of 69 yr and its 138 yr subharmonic. The final model solution, selected from 29 alternative combinations of the model parameters using Mallows's Cp metric, revealed a statistically significant deterministic trend, 0.40 ± 0.03 °C/c (p < 0.01), and acceleration, 0.67 ± 0.11 °C/c2 (p < 0.01) explaining 33% of the global sea surface temperature variations. The combined yearly trend and acceleration in global sea surface temperature as predicted by the model, exhibit a strong correlation with the yearly increase in the global CO2 concentrations observed during the 20th century. Keywords: Climate change, First order autoregressive model, Global sea surface temperature, Global sea surface temperature acceleration, Global CO2 concentratio

The Effect of Warming Oceans at a Tide Gauge Station

This study proposes a new paradigm for assessing thermosteric effects of warming oceans at a tide gauge station. For demonstration, the trend due to the global thermosteric sea level at the Key West, FL tide gauge station was estimated using the tide gauge measurements and the global sea surface temperature anomalies that were represented by yearly distributed lags. A comparison of the estimate with the trend estimate from a descriptive model revealed that 0.7±0.1 mm/yr, (p<0.01), of the total trend 2.2±0.1 mm/yr (p<0.01) estimated using the descriptive model can be attributed to the global warming of the oceans during the last century at this station. The remaining 1.5±0.1 mm/yr, 70 percent of the total trend, is the lump sum estimate of the secular changes due to the eustatic, halosteric, and various local isostatic contributions

Thermosteric contribution of warming oceans to the global sea level variations

Thermosteric contribution of warming oceans to the global sea level variations during the last century was evaluated at globally distributed 27 tide gauge stations with records over 80 years. The assessment was made using a recently proposed lagged model inclusive of a sea level trend, long and decadal periodicities, and lagged sea surface temperature measurements. The new model solutions revealed that almost all the long period periodic sea level changes experienced at these stations can be attributed to the lagged thermosteric effects of the warming oceans during the 20th century. Meanwhile, statistically significant (p<0.05) anomalous thermosteric contributions to the secular trends, some of them as large as 1.0±0.2 mm/yr, were detected at six tide gauge stations close to the equator and open seas. The findings of this study revealed a more complex impact of the warming oceans at the globally distributed tide gauge stations other than a secular contribution to the sea level trends of the previous studies

More confounders at global and decadal scales in detecting recent sea level accelerations

The residuals of 27 globally distributed long tide gauge recordswere scrutinized after removing the globally compounding effect of the periodic lunar node tides and almost periodic solar radiation’s sub and superharmonics from the tide gauge data. The spectral analysis of the residuals revealed additional unmodeled periodicities at decadal scales, 19 of which are within the close range of 12–14 years, at 27 tide gauge stations. The amplitudes of the periodicitieswere subsequently estimated for the spectrally detected periods and they were found to be statistically significant (p «0.05) for 18 out of 27 globally distributed tide gauge stations. It was shown that the estimated amplitudes at different localities may have biased the outcome of all the previous studies based on tide gauge or satellite altimetry data that did not account for these periodicities, within the range −0.5 – 0.5 mm/yr., acting as another confounder in detecting 21st century sea level rise