Abstract
Low frequency internal signals bring challenges to signify the role of anthropogenic factors in sea level rise and to attain a certain accuracy in trend and acceleration estimations. Due to both spatially and temporally poor coverage of the relevant data sets, identification of internal variability patterns is not straightforward. In this study, the identification and the role of low frequency internal variability (decadal and multidecadal) in sea level change of Fremantle tide gauge station is analyzed using two climate indices, Pacific Decadal Oscillation (PDO) and Tripole Interdecadal Pacific Oscillation (TPI). It is shown that the multidecadal sea level variability is anticorrelated with corresponding components of climate indices in the Pacific Ocean, with correlation coefficients of −0.9 and −0.76 for TPI and PDO, respectively. The correlations are comparatively low on decadal time scale, −0.5 for both indices. This shows that internal variability on decadal and multidecadal scales affects the sea level variation in Fremantle unequally and thus, separate terms are required in trajectory models. To estimate trend and acceleration in Fremantle, three trajectory models are tested. The first model is a simple second-degree polynomial comprising trend and acceleration terms. Low passed PDO, representing decadal and interdecadal variabilities in Pacific Ocean, added to the first model to form the second model. For the third model, decomposed signals of decadal and multidecadal variability of TPI are added to the first model. In overall, TPI represents the low frequency internal variability slightly better than PDO for sea level variation in Fremantle. Although the estimated trends do not change significantly, the estimated accelerations varies for the three models. The accelerations estimated from the first and second models are statistically insignificant, 0.006 ± 0.012 mm yr−2 and 0.01 ± 0.01 mm yr−2, respectively, while this figure for the third model is 0.018 ± 0.011 mm yr−2. The outcome exemplifies the importance of modelling low frequency internal variability in acceleration estimations for sea level rise in regional scale.
Highlights
Sea level is rising due to the global warming and anthropogenic factors and the rate of the rise are investigated regionally and globally in numerous studies (Douglas, 1992; Church and White, 2006; Merrifield et al, 2009; Haigh et al, 2014; Dangendorf et al, 2019)
When the variation of multidecadal sea level anomaly (SLA) (Figure 2, lower panel) from 1990 onward is considered, it is evident that it is nothing but the low frequency internal variability aliased into the acceleration term in the trajectory model of these studies
Even though two climate indices used in this study show significant anti-correlation with sea level on multidecadal time scale, they do not completely explain the multidecadal variability in this station
Summary
Sea level is rising due to the global warming and anthropogenic factors and the rate of the rise are investigated regionally and globally in numerous studies (Douglas, 1992; Church and White, 2006; Merrifield et al, 2009; Haigh et al, 2014; Dangendorf et al, 2019). When the variation of multidecadal SLA (Figure 2, lower panel) from 1990 onward is considered, it is evident that it is nothing but the low frequency internal variability aliased into the acceleration term in the trajectory model of these studies. This issue is surfaced in Scafetta (2014) which has estimated acceleration in Fremantle for different time intervals (refer to Table 1 of the study for more information). Proper modelling of the internal variability as well as using proper noise mode are essential elements in assessing the acceleration or deceleration analyses
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
