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End of 20th century broke global cooling trend

Rising temperatures and productivity are inversely proportional - at least around Lake Zurich Keystone

A groundbreaking study from the University of Bern has for the first time shed light on Earth’s temperature patterns over the past two millennia. After a long cooling trend, 1971 to 2000 was found to be the warmest period in 1,400 years.

Using 511 local climate archives from all seven continents, researchers involved in the university’s PAGES (Past Global Changes) programme catalogued past temperature patterns based on tree rings, pollen, coral, the dimensions of lakes and oceans, stalagmites, ice cores and historic documents.

They found that global temperatures fluctuated in specific regional patterns but that all regions except Antarctica saw a long-term cooling trend followed by significant warming in the past 30 years. However, each region also experienced trends of its own.

“Marked periods like the warming anomaly in the Middle Ages or the small ice age come up on a regional level but don’t show a single global picture,” said Heinz Wanner, the study’s lead researcher.

For example, the warming trend seen at the end of the 20th century, between 1971 and 2000, was twice as big in the northern hemisphere as in the southern, according to the research.

What’s more, those years didn’t mark record temperatures for all regions; in Europe, for example, the period between 80BC and 21BC was probably warmer than the most recent 30 years.

About 80 researchers were involved in the project, which has been underway since 2006. The results appeared in the Nature Geoscience journal.

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SWI - a branch of Swiss Broadcasting Corporation SRG SSR