A study of marine sponges has found global temperature rises may have already exceeded 1.5 degrees.

The University of Western Australia-led research extracted 300 years of ocean temperature records preserved in ancient sea sponges.

Lead author Emeritus Professor Malcolm McCulloch said the records showed global warming had been underestimated by 0.5 degrees.

That was because the records in the early industrial era were poor and limited by shipping routes, he said.

"So rather than the Intergovernmental Panel on Climate Change estimate of average global temperatures having increased by 1.2 degrees by 2020, temperatures were in fact already 1.7 degrees above pre-industrial levels.

"The clock of climate change has been brought forward by about a decade by our findings. So things that we're thinking would have happened 10 years hence are actually happening now."

The research raises the question of whether average temperatures have exceeded the Paris Agreement, aimed at keeping warming to below 2 degrees - or whether they will soon.

McCulloch wants climate change action to focus on reducing emissions rather than a maximum global warming threshold.

He said attempts to reduce emissions had been dismal.

"To me, we have to change the message somewhat. Rather than having these convenient, 'no more above two degrees', which actually simplifies the problem too much. We have to say, the answer is we have to reduce emissions and we have to have targets and we have to meet those targets".

McCulloch said the study made it even more urgent to halve emissions by early 2030, and no later than 2040.

- RNZ