MELBOURNE: Global warming over the 20th century has produced the hottest global average temperatures in 1400 years, a major scientific study has found.
Scientists have found that the period between 1971-2000 was warmer than any other time in nearly 1400 years.
The first continental-scale reconstruction of temperatures over the past 2000 years by an international team of scientists has highlighted the unusual nature of the 20th century warming.
Recent warming reversed the long-term cooling, during the period 1971?2000, when the average temperature was higher than any other time in nearly 1,400 years, according to the study published in Nature Geoscience.
Researchers, combining Northern and Southern Hemisphere temperature reconstructions, found that the 20th Century warming is a global event that has produced the hottest global average temperature in 1400 years.
This is in stark contrast to the Medieval Warm Period and Little Ice Age, which the study revealed did not occur simultaneously across the globe.
"The striking feature about the sudden rise in 20th Century global average temperature is that it comes after an overall cooling trend that lasted more than a millennium," said Dr Steven Phipps, author of the paper from the University of New South Wales' ARC Centre of Excellence for Climate System Science.
"This research shows that in just a century the Earth has reversed 1400 years of cooling," Phipps said.
The researchers used data from 511 individual proxy records. The majority of these records came from tree ring measurements but also included coral reefs, cave formations, ice cores, lake sediments and some historical documents.
The 2000-year temperature snapshot revealed by the researchers shows a long-term cooling trend before human influences began to become significant.
This trend was primarily driven by natural cycles in the Earth's orbit. At the same time there were also natural fluctuations caused by volcanic eruptions and variations in solar activity.
It is these natural variations, and in particular the changes in the Earth's orbital cycle, that explain why some of the average global temperatures prior to AD 600 were as warm as today.
However, none of these natural influences account for the dramatic global temperature rises of the 20th century, researchers said.
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