Impacts of warming oceans
A brilliant Wilcox cartoon appeared in the Sydney Morning Herald on 12 March. She used two panels: on the left were reef tourists looking down from a boat at bleached corals; on the right was an actual sea surface temperature (SST) map of the Pacific Ocean sourced to NOAA OISST V2.1(9-3-24). Immediately the message was clear at two scales, one is global, the other what we experience as impacts that can be attributed to climate change.
That same week on 13 March an article appeared in The Guardian stating that ocean temperatures are going “off the charts”. Particular reference was made to the Sydney region where Manly Hydraulics Lab twice recorded SST at 26.75 degrees C that past week; this is 3 degrees above March average. These are Queensland water temperatures! Oceans just love to absorb heat. We can only anticipate more such events as air global temperatures continue to rise. As reported in that paper, Hugh McDowell from the BoM is quoted as saying “We’re seeing unprecedented weather all the time and we’re expecting more extremes with climate change in the future”.
All this drew me to the IMOS Current News website. This is a marvelous source of ocean information, well-illustrated with visualisations of data and clearly written. David Griffin and the IMOS team are to be congratulated in bringing this information to a wide audience. It is a continuous flow of “stories” related to understanding and use of current, SST, and biological material. Angus Gordon reminded me that wearing his sailing cap he has been using IMOS current data for many years in planning his ocean racing tactics. He notes that the strength of flow past headlands is very dependent on the local angle of the current to land. If the current is locally angled towards the headland the current at the headland is far stronger, meaning one needs to go as close as courage would allow. Griffin and Pilo in Ocean Current News of 22 December 2023 highlighted to those racing in the Sydney-Hobart that they would experience “exceptional currents” associated with the presence of warm core eddies. But they went further in alerting boats to beware of tropical basking sunfish given “exceptionally high” SST.
Night after night during this past summer Sydneysiders have swelted under conditions comparable to what folk from Brisbane experience each year. ABC weather presenter Tom Saunders does a great job in communicating the circumstances we have been facing including high wet bulb (dew point) temperatures. The need to understand this measure is as critical in summer as it is in some places in winter to know about wind chill factor. Both require combining two well known measurements, temperature and relative humidity for the former, and temperature and wind for the later. The wet bulb temperature is critical to human health because it relates to the ability of the body to cool itself through sweating. A calculator can be found online with warnings as to what it may mean to you because there are varying individual responses. The point made by Tom Saunders was that warm ocean temperatures were exacerbating the wet bulb temperature increasing the health risk to many.
It is well established that high SST above 26.5 degrees C are a factor in tropical cyclone formation. While it is unlikely for such extreme events to be generated in Tasman Sea waters according to the BoM, there are concerns that warmer conditions we have just been experiencing may prompt a Coral Sea cyclone to track farther south This is not unprecedented but could it become more severe and more frequent? There is also uncertainty around how longer periods of high SST may interact with other atmospheric factors and trigger an extreme East Coast Low; again this is not unprecedented. Our beaches, dunes and estuaries await their arrival! And don’t forget higher SST can induce higher sea levels.
The movie star named Nemo made many aware of not just the existence of the EAC, but also that it is warming. Over last two decades a group of fish biologists have been tracking changes in fish and other marine species down the east coast. I have had the pleasure of knowing one of these intrepid scientific divers, David Booth from UTS. He has guided Irene and me on snorkel swims at a couple of Sydney locations. Last week I met up with him at Parsley Bay where he and his partner were placing cameras underwater. They are working with a large group of scientists from Sydney Institute of Marine Science (SIMS), Australian Museum and NSW Fisheries, along with citizen scientists, documenting fish life in the Harbour (see J. Battista et al. 2022 “A comprehensive analysis of all known fishes from Sydney Harbour”, Marine Pollution Bulletin, 185 (2022) 114239). The latest count is 675 species, amazing. This paper discusses how climate change through warming the EAC has influenced an influx of tropical fish larvae that has successfully settled as juveniles in summer months. Warmer winter months greater than 18 degrees C are seen as more favourable for the survival and reproduction of the fish. Booth and Sear in 2018 have also written about coral expansion and coral associated fishes in Sydney waters (Coral Reefs, 37, 395).
As we proceed down this uncertain path of climate change I would invite your thoughts and observations of what impacts you would attribute to this new climate era. It may not just be a case of being “unprecedented” (a somewhat overused word), but it may be sufficiently unusual as being influenced by global warming.
Bruce Thom
Words by Prof Bruce Thom. Please respect the author’s thoughts and reference appropriately: (c) ACS, 2024. For correspondence about this blog post please email admin@australiancoastalsociety.org.au
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