Swimmers and surfers along the Northern Beaches have been enjoying unseasonably warmer ocean temperatures this winter. But is this something to rejoice, and why is it happening ?
We first picked up on it via Manly’s resident temperature checker, Guy Dunstan, who noticed a spike in the ocean’s temperatures recently, leaving him with uneasy feeling that something wasn’t right.
“About three weeks ago, I noticed that it [the ocean temperature] was abnormally high. And August is always the coldest month of the year… So, it’s about three degrees warmer than normal,” Guy told us, in front of the concrete podium at South Steyne where he chalks up the water’s temperature every day at 4 am.
“That worried me, because it’s the first time I’ve really felt there’s been a shift in the in the pattern of the ocean.”
The former media consultant has been recording the temperature since 2021. The change spooked him into looking at other concerning changes in our waters, many affected by warming waters, such as the red algal bloom on South Australia’s Murray River.
The red algal bloom (or colloquially, the red tide) is naturally occurring; which is the result of rapid and intense growth of microscopic algae in water. There are thousands of these species but only hundreds are considered harmful to marine life and just dozens to humans.
Its rapid growth can be resulted in various factors such as warmer waters or an influx of nutrients from land run-offs.
The algae outbreak in SA is the species Karenia mikimotoi and for months it has devastated their shorelines, killing sea life by the thousands.
The friendlier variant found on the Northern Beaches is known as Noctiluca scintillans – or more locally known as the pretty, bright-blue bioluminescent you’ll see breaking on summer night shorelines.
Footage from a local shows a potential appearance of the algae around Shelly waters this week, a few months earlier than usually expected. Northern Beaches local and Swellnet meteorologist Craig Brokensha says this could be due to the warmer temperatures and nutrient run-off from Sydney’s recent wild weather. And although there is no immediate cause for concern, it should be monitored.
“We’ve got the warm water and the rain events, and that puts fertilisers and nutrients into the system that can cause those blooms. Most of them aren’t too harmful, as long as they don’t hang around too long. But as we’ve seen in South Australia, there are the harmful algal bloom species. So it’s something we’ll have to be definitely take into account into the future,” Craig told Manly Observer.
Our local bioluminescence isn’t considered a threat to humans, but high densities can be harmful to surrounding marine life as they release toxic ammonia, and cause oxygen depletion in water. However, unlike the more stagnant water systems in the South Australian Gulf, Manly has the benefit of the East Australian Current which is pretty decent at cycling water systems.
Why is the water warmer?
Turns out, our temperature guy, Guy, was right to be worried about warmth: models show it’s actually part of a five year global trend, with no signs of cooling off. In fact, the sea surface level temperature records have been broken two times in the past three years; the most recent being in March 2024 at 26.75 degrees.
“As a surfer, I remember the frigid mornings where we had to wear 4/3 [mm wetsuit], and the water was freezing, but now you jump in and it feels… not like a bath, but relative to the outside cold temperatures, it’s much more milder,” Craig said.
“This time of year is when we get the coolest sea surface temperatures, because there’s a bit of a lag between the solar heating and then the winter passing. But it’s currently around two to three degrees above average.”
Craig says the temperature trends are the result of a warming climate, as well as back to back La Ninas. This weather system typically heats up water surface temperatures by pushing over accumulations of warm waters over from the western Pacific Ocean, via east trade winds, towards South-East Asia. It then flows through the Coral Sea into the East Australian Current, eventually arriving at Sydney.
The warmer local waters have also seen a resurgence in subtropical coral and tropical fish – so, surprisingly, there are some benefits to the rising temperatures.
For surfers like Craig, the premature rise in temperatures offer a warm welcome during those early morning paddle outs. La Nina patterns also pick up East swell, which hits the Northern Beaches better.
“There are pluses for surfers, but for the climate, it’s not great,” Craig conceded.
The Long Term Downside
Unfortunately the downsides, long term, are significant. Warmer water offshore can generate higher intensity downpours, flash flooding and even tropical cyclones.
That’s not just bad news for our safety, it hits the hip pocket too.
Insurance companies have picked up on this trend and are now issuing premiums or rendering some locations uninsurable if they’re in a high climate risk area.
It’s something local federal MP Zali Steggall (and Mackellar counterpart Dr Sophie Scamps) have warned about for some time.
“Our local governments are meeting the cost of all the cleanups and all the storms, and their insurance premiums are going up. And then we’re paying for it as residents, again, through levies. So I have a real issue,” Steggall told our editor this year.
The federal representative also pointed out that living in an uninsurable area may make the process of applying for a mortgage – amidst an already prominent housing crisis – unachievable. “There are whole regions that are uninsurable… the banks are going to have to decide at what point the risk is a million dollar mortgage on a property that’s not insured for an event that’s likely to happen every few years.”
In just the past three years, insurance premiums have gone up by 32 per cent in areas considered associated with climate risks, and this is evident right on our doorstep.
According to the Climate Council’s climate risk map, 14.5 per cent of properties in the region of Mackellar are at a moderate to high risk of climate related hazards, Warringah is at 5.4 per cent, an almost half percent increase since June.
Earlier this year, Ms Steggall told us she is working on a proposal with the Federal Government to legislate national climate risk assessments and adaption plans for more transparency on where to implement action. A ‘resilient building scheme’ was also mentioned to be in the works which would involve a publicly funded body to improve the resiliency of homes, eventuating in a climate resilient certificate which could be recognised by banks or insurers.
Although Australia’s carbon footprint is relatively small in comparison to the rest of the world, Craig added there are little things that can be done to make the best out of a bad situation.
“Water capture and storage. The East Coast gets so much of this rainfall, and out in South Australia, Western Victoria, they’re missing out. So whether there’s some way in the future we can store that…” he said.
“I know they said it’s cost too much to pump across back to those states, but we definitely need to be adapting to this changing climate.”
Written by Jack Kelly
Edited by Kim Smee
