Scientists Use Giant Clams To Show That Temperatures Were Warmer In The Middle Ages

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Michael Bastasch DCNF Managing Editor
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Clams hold pearls and insights to Earth’s climate history. Two recent studies examining clams and coral samples in the South China Sea suggest the climate was warmer during the Medieval period than during modern times.

Two studies out of the Chinese Academy of Sciences found that the climate was warmer in the Roman and Medieval warm periods than today, despite much lower atmospheric concentrations of carbon dioxide.

“This new paper adds further material to the substantial body of real-world proxy evidence establishing that today’s global temperature is within natural ranges of past changes,” Dr. Hong Yan with the Institute of Earth Environment at the Chinese Academy of Sciences.

Studying giant clams and coral reefs, scientists were able to reconstruct sea surface temperature changes going back 2,500 years. What the clam and coral data show is the Roman and Medieval warming periods impacted East Asia and the western Pacific. The study provides further evidence against the theory that there was little global temperature variation until the 20th century.

Both Chinese studies provide evidence for what is called the Medieval Warm Period, which took place during the late Roman Empire and Middle Ages. The period preceded a time of cooling known as the Little Ice Age.

The dominant theory among climate scientists is that the Medieval Warm Period and the Little Ice Age were relegated to the Northern Hemisphere, specifically over Europe. But new evidence shows that Middle Ages warmimg may have been more widespread than previously thought.

“The UN’s climate panel should never have trusted the claim that the Medieval Warm Period was mainly a European phenomenon. It was clearly warm in South China Sea too,” said Dr. Willie Soon of the Harvard-Smithsonian Center for Astrophysics.

These two Chinese studies piggyback on a Swedish study from last year also claiming that the climate was warmer during Roman and Medieval times. The Swedish study looked at radiocarbon-dated mega-fossils in the Scandes mountains and tree lines to make its determination.

Swedish scientists wrote that “summer temperatures during the early Holocene thermal optimum may have been 2.3°C higher than present.” The “Holocene thermal optimum was a warm period that occurred between 9,000 and 5,000 years ago. This warm period was followed by a gradual cooling period.”

There is also evidence of warming in Japan and North America during the Middle Ages. For example, researchers have found that in Japan between “AD 700 and 1200… there was about a 1°C rise in average temperature” that “appears to be related to the ‘Medieval Warm Period.'”

This stands in sharp contrast to temperatures from AD 1580 to 1700 when “temperatures were about 2°C below the long-term pre-1850 average during the multi-century Little Ice Age.”

[h/t Watts Up With That]

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