According to research by the University of New South Wales (UNSW), at times this year, the water temperature off Narooma was "up to four degrees warmer than normal".
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In fact the study into how coastal waters adjacent to the Eastern Australian Current have warmed over the last 25 years - published in the journal, Geophysical Research Letters - found that the ocean off Narooma and Sydney has become warmer at a rate of almost half a degree per decade - .48 degrees per decade to be precise. The global average is .12 degrees per decade according to the study.
This means that, on average, the sea near Narooma is now 1.5 degrees warmer than it was 30 years ago study's lead author and Postdoctoral Research Fellow in UNSW Science's School of Mathematics and Statistics, Dr Neil Malan said.
"These numbers are accelerating off southern NSW: at times this year the water temperature there was four degrees warmer than normal. The fact that the trend is so large, and that it's more than three times greater than the global average and that Narooma is such a hotspot, is shocking," he said.
"What really surprises me is the raw numbers and the effect of climate change, what half a degree per decade actually means for an ecosystem or for an environment in 10 or 20 years."
Dr Malan said an example of the impact this could have was shown by 2016 study by Macquarie University which found that Montague Island penguins were avoiding warmer waters and swimming further from home to hunt in cooler locations."
The UNSW study used data from over 10 years of measurements of actual water temperatures from five sites: North Stradbroke Island (average increase in water temperate; 0.22 degrees per decade), Coffs Harbour (average increase; 0.16 degrees per decade), Sydney (0.48 per decade), Narooma (0.48 per decade) and Maria Island off Tasmania (0.41). The study also used satellite estimates of temperatures and currents and a regional ocean model over the last 22 years.
Dr Malan said fast-flowing western boundary currents, like the Eastern Australia Current , move warm water down the coast of NSW, but just north of Sydney it branches off towards New Zealand.
At this point it forms large eddies (rotating bodies of warm ocean water) that are carried along SE Australia.
"Norther NSW water temperatures, while still warming, are more stable as they are not as affected by what is happening offshore. It is southern NSW where we see an increase in eddy activity that is warming the fastest," he said.
Dr Malan said the next area of research will look at longer trends of coastal warming dating back to the 1950s; studying more coastal sites around Australia and looking at the link between deep ocean and coastal water temperatures.
You can read the full study here: agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090751
