Over the 12-year period, estuaries heated an average 0.2 degrees a year, to be 2.16 degrees warmer. Shallow estuaries typically warm up faster than nearby seas – especially if they become cut up by low river flows.
The waters also became more acidic at the pace of 0.09 pH units annually, while salinity levels varied depending on how much lagoons or other types of coastal formations interacted with the sea.
While local conditions may play a role, such as urbanisation of some areas, overall the researchers “identified that climate change is the reason these estuaries are changing”, he said.
Climatologists are generally wary about extrapolating large shifts from just a 12-year study. Land and sea temperatures around Australia have warmed about a degree over the past century. Still, Dr Scanes said climate models point to more frequent and severe droughts for much of Australia so the recent period may be a harbinger of conditions to come.
He said the pace of acidification was “happening faster than what you’d expect from carbon-dioxide levels”. While the study did not examine the reasons, lower rain tallies recently may have meant less dilution of minerals that enter rivers naturally through the groundwater, such as hydrogen sulphide.
Professor Ross said the research was based on more than 6000 observations that revealed “a clear pattern”.
Warming in estuaries was roughly twice the pace of air and ocean, and more than triple the pace for lagoons, she said.
The work likely had implications for other parts of Australia, where much of the coast is typically marked by shallow estuaries, as well as other temperate regions such as the Mediterranean, the paper said.
The NSW government said it was working closely with local industries, councils and communities that relied on annual income of more than $100 million from aquaculture such as oyster farming.
“Plants and animals in estuaries may be able to adapt to the changing conditions, or we may see a gradual change to more heat-tolerant types of plants and animals,” a spokeswoman said.
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.