Sydney, Australia - A study of marine sponges has shown that global temperatures may have already risen faster and for longer than previously estimated, according to newly published research.

A team led by Australian scientists extracted ocean temperature records preserved in the calcium carbonate skeletons of long-lived Caribbean sclerosponges.

The researchers found that industrial-era warming began in the mid-1860s, a date consistent with what could be expected from historical records but more than 70 years earlier than suggested by records from ship-based measurements of sea surface temperatures.

University of Western Australia's Professor Malcolm McCulloch said that the finding shows that global warming had been underestimated by about 0.5 degrees Celsius, meaning we're closer than previously thought to the "guardrail" of 1.5 degrees Celsius above pre-industrial levels set by the 2015 Paris Agreement.

Rather than the Intergovernmental Panel on Climate Change estimate of average global temperatures having increased by 1.2 degrees [Celsius] by 2020, temperatures were in fact already 1.7 degrees [Celsius] above pre-industrial levels," McCulloch said in a statement released on Tuesday.

"If current rates of emissions continue, average global temperature will certainly pass 2 degrees [Celsius] by the late 2020s and be more than 2.5 degrees [Celsius] above pre-industrial levels by 2050," he added.

"The now much faster rates of land-based warming also identified in the study are of additional concern, with average land temperatures expected to be about 4 degrees [Celsius] above pre-industrial levels by 2050."

"Keeping global warming to no more than 2 degrees [Celsius] is now the major challenge, making it even more urgent to halve emissions by early 2030, and certainly no later than 2040."

The research was published in Nature Climate Change.