Uploaded December 2023 | Updated September 2026, 1 day ago
1318th Ordinary General Meeting and Open Lecture of the Royal Society of NSW — 29 November 2023
"What do we really know about 20th- and 21st-century sea-level change"
Emeritus Professor John Church AO FAA FTSE FAMS FAGU
Climate Change Research Centre
UNSW Sydney
https://royalsoc.org.au/blog/1318th-ogm-and-open-lecture
The presentation commences at 00:46
Timing Marks:
00:00:00 Introduction to the Speaker: Dr Susan Pond AM FRSN FTSE FAHMS, President, Royal Society of NSW
00:00:46 Presentation: Professor John Church, winner of the RSNSW 2022 James Cook Medal
00:39:33 Q&A session: Moderated by Mr Guy Loucks, Program Committee, Royal Society of NSW
00:50:49 Meeting Close
Summary: Accelerating sea-level rise in much of the world will result in growing impacts through the 21st century and beyond. Despite the clear identification of an accelerating rise, many uncertainties remain. Understanding historical sea-level change is a prerequisite for building confidence in useful and accurate predictions of future changes.
For many decades, our limited knowledge of the contributions to sea-level change could not explain the rise measured by coastal tide gauges — the sea level enigma. New and improved in situ and satellite observations of the ocean, improved understanding of the “solid Earth”, and better understanding and improved modelling of the climate system have helped resolve this enigma. A number of recent studies have argued that the sum of contributions from both observations and model estimates to sea-level change over the satellite era, the last half century, and since 1900 adequately explains the observed sea-level rise, which means the sea-level budget is closed. The major contributions are from ocean thermal expansion and contributions from glaciers, with an accelerating ice sheet contribution over the recent decades.
Our recent work has explored the sensitivity of global and regional sea-level reconstructions to poorly known land motions and the factors causing temporal and regional variations in the rate of rise. With this knowledge, existing reconstructions of global mean sea level are mostly not significantly different from each other from 1900 to the present, both in the time-averaged rate and the temporal variability. However, while the average rate from 1900 to the present is similar to that from the sum of contributions, the rate of reconstructed GMSL rise is significantly smaller/larger than the sum of contributions prior to 1940/after 1970. Why is this? What do we really know? What are potential explanations for this continuing enigma?
And what can we project about future sea levels, both for the 21st century and beyond? And can we constrain projections for the 21st century and beyond?
1318th Ordinary General Meeting and Open Lecture of the Royal Society of NSW — 29 November 2023
"What do we really know about 20th- and 21st-century sea-level change"
Emeritus Professor John Church AO FAA FTSE FAMS FAGU
Climate Change Research Centre
UNSW Sydney
https://royalsoc.org.au/blog/1318th-ogm-and-open-lecture
The presentation commences at 00:46
Timing Marks:
00:00:00 Introduction to the Speaker: Dr Susan Pond AM FRSN FTSE FAHMS, President, Royal Society of NSW
00:00:46 Presentation: Professor John Church, winner of the RSNSW 2022 James Cook Medal
00:39:33 Q&A session: Moderated by Mr Guy Loucks, Program Committee, Royal Society of NSW
00:50:49 Meeting Close
Summary: Accelerating sea-level rise in much of the world will result in growing impacts through the 21st century and beyond. Despite the clear identification of an accelerating rise, many uncertainties remain. Understanding historical sea-level change is a prerequisite for building confidence in useful and accurate predictions of future changes.
For many decades, our limited knowledge of the contributions to sea-level change could not explain the rise measured by coastal tide gauges — the sea level enigma. New and improved in situ and satellite observations of the ocean, improved understanding of the “solid Earth”, and better understanding and improved modelling of the climate system have helped resolve this enigma. A number of recent studies have argued that the sum of contributions from both observations and model estimates to sea-level change over the satellite era, the last half century, and since 1900 adequately explains the observed sea-level rise, which means the sea-level budget is closed. The major contributions are from ocean thermal expansion and contributions from glaciers, with an accelerating ice sheet contribution over the recent decades.
Our recent work has explored the sensitivity of global and regional sea-level reconstructions to poorly known land motions and the factors causing temporal and regional variations in the rate of rise. With this knowledge, existing reconstructions of global mean sea level are mostly not significantly different from each other from 1900 to the present, both in the time-averaged rate and the temporal variability. However, while the average rate from 1900 to the present is similar to that from the sum of contributions, the rate of reconstructed GMSL rise is significantly smaller/larger than the sum of contributions prior to 1940/after 1970. Why is this? What do we really know? What are potential explanations for this continuing enigma?
And what can we project about future sea levels, both for the 21st century and beyond? And can we constrain projections for the 21st century and beyond?
