Australasia at its hottest in 1000 years - report

01:20, May 18 2012

The last 60 years have been the hottest in Australasia for a millennium, most likely thanks to human-caused climate change, a new report says.

Scientists from the University of Melbourne used 27 natural climate records, including tree rings, corals and ice cores to create the first large-scale temperature reconstruction for the region over the past 1000 years.

"Our study revealed that recent warming in a 1,000-year context is highly unusual and cannot be explained by natural factors alone, suggesting a strong influence of human-caused climate change in the Australasian region," Joelle Gergis, the study's lead researcher, said.

The climate reconstruction was done 3000 different ways, showing with 95 per cent accuracy that there were no other warm periods in the past 1000 years that matched or exceeded post-1950 warming observed in Australasia.

"What we see from the reconstruction is the late twentieth century, 1971 to 2000, was .34 degrees warmer than average pre-industrial conditions," Gergis said.

"The warmest 30-year pre-industrial period is between 1238 to 1267, but this is not significantly warmer than present. The best estimate of this temperature anomaly is less than one tenth of degrees Celsius below 1961 to 1990 level."

Gergis said the three warmest decades of the past 1000 years occurred consecutively in the 1970s, 1980s, and 1990s.

Direct temperature records showed that 2000 to 2010 was the warmest decade since modern records were available.

Gergis said the 1830s and 1840s were the coldest decades, coinciding with the global "Little Ice Age".

The study used palaeoclimate, or natural records, which were fundamental in evaluating regional and global climate variability over centuries before temperature records began in 1910.

Gergis used the natural records provided by more than 30 researchers from New Zealand, Australia and around the world.

Steven Phipps, from the Climate Change Research Centre at the University of New South Wales, who did the modelling, said the study demonstrated there was a strong human influence in the region.

"The models showed that prior to 1850 there were not any long-term trends and temperature variations were likely to be caused by natural climate variability which is a random process," he said.

"But [the modelling showed] 20th-century warming significantly exceeds the amplitude of natural climate variability and demonstrates that the recent warming experience in Australia is unprecedented within the context of the last millennium."

Niwa's principal climate scientist Jim Renwick today said the findings backed recent studies in New Zealand.

"[The study] fits in with reconstruction that has been done in the New Zealand region. There has been quite a bit of work done here, and they show that the trends we've seen in temperature over the last 100 years or so are outside of the variability that we've seen earlier," he said.

Reliable temperature records in New Zealand began around 1910 and since 1970 every decade had been warmer than the last.

Renwick said temperatures were about .5C warmer than before the 1950s.

Though local studies painted a picture of climate change over the past century, Renwick said the latest study showed a clear indication of long-term trends.

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