“Warming oceans cause sea levels to rise, both directly via heat expansion, and indirectly through melting of ice shelves. Warming oceans also affect marine ecosystems, for example through coral bleaching, and play a role in weather events such as the formation of tropical cyclones” [The Conversation, 14 September 2021, reporting on research by Kewei Lyu, Xuebin Zhang & John A. Church]
This is a Australian Bureau Of Meteorology visualisation of sea surface temperatures around the Australian coastline on 4 August 2023 as El Niño conditions continue to be expected to arrive within weeks.
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On 1 August BOM stated:
The Bureau's El Niño Alert continues, with El Niño development considered likely in the coming weeks, despite the current lack of atmospheric response. When El Niño Alert criteria have been met in the past, an El Niño event has developed around 70% of the time.
Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Niño thresholds, with climate models indicating this is likely to continue at least through to the end of the year. In the atmosphere, however, wind, cloud and broad-scale pressure patterns mostly continue to reflect neutral ENSO conditions. This means the Pacific Ocean and atmosphere have yet to become fully coupled, as occurs during El Niño events. El Niño typically suppresses winter–spring rainfall in eastern Australia.
And this is what is being discussed by climate scientists in our region.
Asia Oceania Geosciences Society, 20th Annual Conference, Axford Medal Lecture given by UNSW Emeritus Professor John Church, 2 August 2023:
What do we really know about 20th and 21st Century Sea-Level Change?
Abstract: 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 contributions 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 to each other from 1900 to the present, both in the time-averaged rate and the temporal variability. However, while the average rate over 1900 to 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 level, both for the 21st century and beyond. And can we constrain projections for the 21st century and beyond?
One of the notable take-aways from this lecture appears to be:
..that one of the main impacts of sea level on society will be how we adapt.
“We will have to adapt to that sea level rise we can no longer prevent. Of particular concern is very significantly increased rates of coastal flooding events and eventually inundation of some coastal areas,” Prof. Church said.
“We are already experiencing more severe and more frequent coastal flooding events impacting an increasing number of people.
“This century, we could expect up to about a metre of sea level rise with unmitigated emissions. This could rise to several metres over coming centuries. Today, an estimated 200 million people live within one metre of current high tide level, and by mid-century over a billion people are likely to live in the low elevation coastal zone, which is within 10 metres of current sea level.” [UNSW Newsroom, “'Urgent action is required’: UNSW climate expert on what’s to come as sea levels rise”, 2 August 2023]
A reminder that much of the NSW Northern Rivers coastal region is predicted to experience significant levels of inundation at an average global surface temperature rise of 1.5°C.
Climate Central, north-east NSW (Northern Rivers) mapping, 2021. Click on image to enlarge
BACKGROUND
John Church is an Emeritus Professor in the Climate Change Research Centre, University of New South Wales. He has published across a broad range of topics in oceanography.
His area of expertise is the role of the ocean in climate, particularly anthropogenic climate change, and in understanding global and regional sea-level rise. He is the author of over 180 refereed publications, over 110 other reports and co-edited three books. He was co-convening lead author for the Chapter on Sea Level in the IPCC Third and Fifth Assessment Reports. He was awarded the 2006 Roger Revelle Medal by the Intergovernmental Oceanographic Commission, a CSIRO Medal for Research Achievement in 2006, the 2007 Eureka Prize for Scientific Research, the 2008 AMOS
R.H. Clarke Lecture, the AMOS Morton Medal in 2017, a joint winner of the BBVA Frontiers of Knowledge Climate Change Category Prize in 2019, the AAS Jaeger Medal in 2021 and the Royal Society of NSW James Cook Medal in 2022. He is an Officer of the Order of Australia, a Fellow of the Australian Academy of Science, the Australian Academy of Technology and Engineering, the American Geophysical Union, the American Meteorological Society and the Australian Meteorological and Oceanographic Society.
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