Taking a dip at Sydney's beaches remains an attractive option even this far into the autumn, and the projections of climate change mean you soon won't have to be an ice-berger to swim year round.

"Sydney will have tropical waters by between 2040-60," Adriana Verges, a marine ecologist at the University of NSW, said. "Summers [will be] above 25, winter 19 degrees."

Regions such as these 12-metre strands of giant kelp off Tasmania are under threat as waters warm. Credit:Craig Sanderson

Those celebrating the future demise of the wetsuit, though, might want to take a look beyond the shallows.

A paper published in Geophysical Research Letters this month highlighted the extent of warmth wasn't being captured by the readily available surface temperature measurements.