20th century reverses 1400 years of global cooling
The 20th century has seen an almost complete reversal of over 1400 years of constant cooling temperatures, a new international study has found.
The study by 78 scientists from 24 countries has highlighted the unusual warming period of the 20th century, concluding that the Medieval Warm Period and the Little Ice Age did not occur simultaneously across the globe.
Co-author of the paper, University of New South Wales’ Dr Steven Phipps, said that the striking feature about the sudden warming period of over th 20th century was that it comes after an overall cooling trend that lasted over a millennium.
“This work has transformed our understanding of temperatures over the past 2000 years,” Dr Phipps 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 accurately reconstruct 2,000 years of global temperatures, researchers used data from over 500 proxy records, including tree ring measurements, coral reefs, cave formations, ice cores and lake sediments.
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.
Palaeoclimatologist Professor Jonathan Overpeck from the University of Arizona, US who is a Visiting Fellow of the Victorian Centre for Climate Change Adaptation Research at the University of Melbourne and Visiting Scientist with the ARC’s Centre of Excellence For Climate System Science, said the work was very exciting.
“The work has confirmed that there was no period of global warmth similar to that of the last 60 years in the preceding circa 2000 years, and adds to the evidence that the so-called Medieval Warm Period was quite different from the recent period of human-caused warming,” Professor Overpeck said.
“This paper has provided confirmation that recent global and continental scale warming was very unusual in recent Earth history, and that this recent warming is driven mostly by human emissions of greenhouse gases.