Data Watch: Sea Level Rise

Who would have thought that sea level would exhibit volatility? Latest data from the U.S. government agency the National Oceanic and Atmospheric Administration (NOAA) to mid-January shows sea level rise pushing to the top of its twenty-year trend line. But only a little more than a year ago sea level exhibited a significant drop of 5 mm (and the “climate skeptic” blogosphere was alight with the claim that sea level rise had stopped). The drop was related to a sudden transition from El Nino to La Nina conditions which dumped an unprecedented amount of water on land. An explanation by NASA of this phenomenon is here.

A good backgrounder on sea level rise can be found at Real Climate (here and here) by Stefan Rahmstorf, one of the world’s foremost experts on sea level.

The major sea level time series all show sea level rising at roughly 3 mm per annum linear rate over the past two decades.

NOAA Sea Level  jpg

In order for us to experience the more pessimistic sea level rise outcomes of 1 to 2 metres by end of century (see for example here), the rate of rise will need to break out of its linear 3 mm per annum trend in the not too distant future. High rates of sea level rise have the potential to cause massive economic disruption, so a careful tracking of any change in trend is a critical component in gauging climate risk.

For your reference, data on sea level rise can be accessed from four main sources: NOAA, The University of Colorado’s CU Sea Level Research Group, the Australian government’s national science agency The Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the French Space Agency related Archiving, Validation and Interpretation of Satellite Oceanographic data centre (AVISO).

Sea level rise is not communicated very well to the general public. Unlike Arctic sea ice extent, which has the wonderful National Snow and Ice Data Center (NSIDC) web site, the major sea level-related institutes traditionally concerned themselves with an academic audience (although CISRO and NOAA have made big improvements over the last couple of years at reaching out to the general public). Publication of data (collected on a rather strange 10-day interval) is haphazard and has considerable lags (please can we have a regular publication schedule clearly indicated). The NOAA and AVISO sites appear to be the most timely in the release of data.

Three counter-intuitive aspects of sea level rise:

1. An Annual Cycle (via the CISRO site)

Sea Level Seasonal Cycle

2. Regional Variability (via the CISRO site)

Sea Level Regional Variation jpg

3. An El Nino Southern Oscillation (ENSO) Cycle (via the AVISO site)

ENSO and Sea Level jpg

The CISRO site also has an animation tracking sea level over the 1997/98 El Nino here. Run the animation and see the amazing 60 cm divergence between the western and eastern Pacific in 1997/98. And I always used to think that water would find its level!

Lastly, a call to would-be bloggers. Is there a sea level wonk or keen post-grad out there who would like to reach out to a wider audience? Arctic sea ice extent has the incomparable Neven. In the year 2050, I would wish (for my children’s sake) that we have transcended the current climate threat and are in a position to award medals to those who stood up and fought. Neven would certainly be one of those at the top of my list for a climate communication Victoria Cross or Medal of Honor in his calm chronicling of the threat we face. The sea level candidacy is currently vacant (but if I am missing someone, please let me know).

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