Proving sea levels are rising
Sea levels are rising, but how do we know? The first in a series on the history of climate change research.
In 1933, a Finnish oceanographer and politician called Professor Rolf Witting visited Lisbon to attend a meeting of the International Union of Geodesy and Geophysics.
Whilst there, he argued passionately for the need to create an international committee to monitor global sea levels, explaining that: ‘For the study of the tides and the tidal currents, of other movements of the sea surface and of currents of different origin, continual observations of sea level are the sole or a most valuable basis.’
The other delegates agreed, and the Mean Sea Level Committee was born. British oceanographer Professor Joseph Proudman of the University of Liverpool Tidal Institute was named secretary of the committee (which later became known as the Permanent Service for Mean Sea Level or PSMSL) and the group set about compiling monthly and yearly data from as many tide gauges as possible throughout the world.
Now, 88 years on, the PSMSL dataset consists of over 2100 mean sea level records from across the globe, the longest of which date back to the start of the 19th century. The data is made freely available to anyone, and most studies of 20th century global sea level rise — including Assessment Reports by The Intergovernmental Panel on Climate Change (IPCC ) -are based on PSMSL data.
Thanks to PSMSL data, we now believe that global mean sea level has risen about 21–24cm since 1880.
The attendees of the 1933 meeting could not have imagined the true impact that the committee has had on our understanding of climate change. Indeed, biographies of Joseph Proudman rarely list his chairmanship of the committee amongst his many achievements.
Current leader of the PSMSL, Elizabeth Bradshaw: ‘Initially the committee was set up to study ocean circulation and dynamics, and it wasn’t until a lot later that the importance of studying climate change became apparent.’
Although some earlier studies suggested that global sea levels may be rising, it wasn’t until the 1970s or even later that scientists had enough good, long-term data to prove it.
Thanks to PSMSL data, we now believe that global mean sea level has risen about 21–24cm since 1880, with about a third of that coming in just the last two and a half decades.
The rising water level is mostly due to a combination of meltwater from glaciers and ice sheets, and thermal expansion of seawater as it warms.
Why this matters
Rising seawater is particularly bad news for the 600 million people in the world currently living in coastal areas. A sea level rise of just half a meter could displace 1.2 million people living in low-lying islands in the Caribbean, Indian and Pacific Oceans.
As well as coastal erosion, rising sea levels exacerbate flooding, and if seawater finds its way into farms and reservoirs it can harm drinking water and crops.
Changing hearts and minds
Rising sea levels is one of the most striking and visual aspects of climate change. We are already seeing the impact rising tides are having on coastal communities around the world. Rates are rising fastest for island nations in the Pacific, whose communities are being forced to leave their homes for good.
However, proving definitively that sea levels are rising has undoubtedly helped convince people, world governments and businesses of the urgent need to act now.
‘The PSMSL provides an essential service, ensuring that sea level data are freely available to all, to study our past and to plan for our future,’ says Elizabeth Bradshaw.
Want to know more?
If you’re a UK taxpayer, your contributions help fund the work of the PSMSL, at the National Oceanography Centre in Liverpool, via UK Research and Innovation — the funding body that allocates government funds for research — and the Natural Environment Research Council.
You can read more about what we do here. And if you liked this article, follow us on Medium, Instagram, Facebook or YouTube — or sign up for our weekly newsletter!
