Melbourne study: Last 100 years reverse 1,400 years of global cooling
A University of Melbourne study of the first continental-scale reconstruction of temperatures over the past 2000 years has found twentieth-century warming was a global event that has produced the hottest global average temperature in 1400 years.
The study by 78 scientists from 24 countries was published in Nature Geoscience and combined Northern and Southern Hemisphere temperature reconstructions has highlighted the unusual nature of the twentieth-century century warming.
The findings are in stark contrast to the Medieval Warm Period and Little Ice Age, which the study revealed did not occur simultaneously across the globe.
The international study led by the Past Global Changes (PAGES) network in Switzerland, included Australian scientists from the University of Melbourne, the ARC Centre of Excellence for Climate System Science at the University of New South Wales and the Australian Antarctic Division.
Co-author of the paper from the University of New South Wales’ ARC Centre of Excellence for Climate System Science Dr Steven Phipps said the striking feature about the sudden rise in twentieth-century global average temperature is that it comes after an overall cooling trend that lasted more than a millennium.
“This work has transformed our understanding of temperatures over the past 2000 years,” he said
“This research shows that in just a century the Earth has reversed 1400 years of cooling. Armed with this information, future researchers will able to better understand the causes of climate variability at a regional and global level and help forecast the changes we can expect as our planet warms.”
To reconstruct 2000 years of temperature, 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came from tree ring measurements but also included coral reefs, cave formations, ice cores, lake sediments and some historical documents.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 showed 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.
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