S. J. Holgate

Evidence for enhanced coastal sea level rise during the 1990s

into 13 regions with near global coverage and using a Glacial Isostatic Adjustment (GIA) model to correct for land movements. We present evidence from altimeter data that the rate of sea level rise around the global coastline was significantly in excess of the global average over the period 1993–2002. We also show that the globally-averaged rate of coastal sea level rise for the decade centered on 1955 was significantly larger than any other decade during the past 55 years. In some models of sea level rise, enhanced coastal riseisapre-cursorofglobalaveragerise.Itremainstobe seen whether the models are correct and whether global-average rates in the future reflect the high rates of coastal rise observed during the 1990s. INDEX TERMS: 1635 Global Change: Oceans (4203); 1223 Geodesy and Gravity: Ocean/ Earth/atmosphere interactions (3339); 4215 Oceanography: General: Climate and interannual variability (3309); 4556 Oceanography: Physical: Sea level variations. Citation: Holgate, S. J., and P. L. Woodworth (2004), Evidence for enhanced coastal sea level rise during the 1990s, Geophys. Res. Lett., 31, L07305,

New Data Systems and Products at the Permanent Service for Mean Sea Level

ABSTRACT Holgate, S.J.; Matthews, A.; Woodworth, P.L.; Rickards, L.J.; Tamisiea, M.E.; Bradshaw, E.; Foden, P.R.; Gordon, K.M.; Jevrejeva, S., and Pugh, J., 2013. New data systems and products at the Permanent Service for Mean Sea Level. Sea-level rise remains one of the most pressing societal concerns relating to climate change. A significant proportion of the global population, including many of the worlds large cities, are located close to the coast in potentially vulnerable regions such as river deltas. The Permanent Service for Mean Sea Level (PSMSL) continues to evolve and provide global coastal sea-level information and products that help to develop our understanding of sea-level and land motion processes. Its work aids a range of scientific research, not only in long-term change, but also in the measurement and understanding of higher frequency variability such as storm surges and tsunamis. The PSMSL has changed considerably over the past 10 years, and the aim of this paper is to update the community about these changes as well as provide an overview of our continuing work.

On the decadal rates of sea level change during the twentieth century

Nine long and nearly continuous sea level records were chosen from around the world to explore rates of change in sea level for 1904 - 2003. These records were found to capture the variability found in a larger number of stations over the last half century studied previously. Extending the sea level record back over the entire century suggests that the high variability in the rates of sea level change observed over the past 20 years were not particularly unusual. The rate of sea level change was found to be larger in the early part of last century (2.03 +/- 0.35 mm/yr 1904 - 1953), in comparison with the latter part ( 1.45 +/- 0.34 mm/yr 1954 - 2003). The highest decadal rate of rise occurred in the decade centred on 1980 (5.31 mm/yr) with the lowest rate of rise occurring in the decade centred on 1964 ( - 1.49 mm/yr). Over the entire century the mean rate of change was 1.74 +/- 0.16 mm/yr

Comment on "A semi-empirical approach to projecting future sea-level rise".

Rahmstorf (Reports, 19 January 2007, p. 368) presented an approach for predicting sea-level rise based on a proposed linear relationship between global mean surface temperature and the rate of global mean sea-level change. We find no such linear relationship. Although we agree that there is considerable uncertainty in the prediction of future sea-level rise, this approach does not meaningfully contribute to quantifying that uncertainty.

Real time sea level data transmission from tide gauges for tsunami monitoring and long term sea level rise observations

The authors present the development and implementation of a ‘tsunami enabled’ tide gauge which allows real time data to be returned from almost anywhere on Earth. At its centre is a low power, embedded Linux platform, which performs the data logging and communications. This is attached to a radar and pressure sensors that are queried over a serial interface. Telemetry is through the Inmarsat Broadband Global Area Network (BGAN) system which allows a bi-directional broadband connection over Ethernet, permitting remote reconfiguration when required, and faster, more frequent tide gauge data. Data transmission is over an internet connection with files containing one minute values from three sensors returned every five minutes

A Study of Delays in Making Tide Gauge Data Available to Tsunami Warning Centers

Abstract This short note provides conclusions of a study of the various factors that determine the delay between tsunami arrival at a tide gauge station and data being made available at tsunami warning centers. The various delays involved include those associated with the tide gauge hardware and measurement methods and with the form of telemetry employed. It is shown that the most widely used form of telemetry in existing tsunami networks (meteorological satellite data collection platforms) can be improved upon significantly with the use of modern telemetry alternatives [notably Inmarsat’s Broadband Global Area Network (BGAN)], enabling faster, more frequent, more secure, and higher bandwidth transmissions of tide gauge data.

Sea level changes at Ascension Island in the last half century

An exercise in ‘data archaeology’ at Ascension Island has provided an estimate of sea level change between 1955 and 2001.5 (the mid-point of a recent dataset spanning 1993–2009). That average trend of 0.93 mm y−1 (SE 0.69) compares to a larger rate during 1993–2009 itself of 2.55 (SE 0.13) and 2.07 (SE 0.30) mm y−1 from tide gauge and altimeter data respectively, suggesting a recent acceleration in sea level rise. An ocean model and steric height datasets have been used for comparison to the measurements, with the conclusion that the acceleration was probably at least partly due to a steric height increase. This exercise is based on only one month of historical tide gauge data and is admittedly on the useful limit for long-term sea level studies. In addition, it is unfortunate that the tide gauge benchmark installed in 1955 has disappeared, even if one can estimate its height relative to modern marks. Nevertheless, the study does provide information of interest to climate studies, enables limits to be inferred on the real changes, and provides background information for other coastal studies. Most importantly, it is intended as a demonstration of the value of similar exercises where short historical records exist.