CONCLUDE

How Adult Americans Think About Climate Change.

USA TODAY

Highlights of the story

  • “There was a global cooling before global warming.”
    ;
  • Global warming has increased by around 1 degree Celsius since the mid-19th century.
  • “Our future climate will largely depend on the influence of human factors.”

Over the past 150 years, man-made global warming has eliminated the natural global cooling that has occurred in the past 6,500 years Study published Tuesday.

Scientists have reconstructed the global average temperature over the past 12,000 years to come to this conclusion. They investigated “paleoclimatic” sources from around the world – such as marine deposits, marine sediments, peat and glacial ice – in order to infer past changes in temperature.

“There was a global cooling before global warming,” study leader Darrell Kaufman, paleoclimatologist at Northern Arizona University, said in a statement.

“Previous work has shown convincingly that the world cooled naturally and slowly for at least 1,000 years before the mid-19th century when the global average temperature, along with greenhouse gas emissions, reversed course.”

“This study, which is based on a comprehensive new compilation of previously published paleoclimate data combined with new statistical analysis, shows more surely than ever that global cooling began on a thousand-year scale around 6,500 years ago,” he said.

The cooling rate that followed the maximum warmth was subtle and was only about 0.1 degrees Celsius per 1,000 years, according to assistant research professor and study co-author Michael Erb, also from Northern Arizona University, who analyzed the temperature reconstructions.

The cooling seems to be driven by slow Earth orbit cycles that reduced the amount of summer sunlight in the northern hemisphere and culminated in the “little ice age” of recent centuries, Erb said.

Global warming has increased by about 1 degree Celsius since the mid-19th century, suggesting that the global average temperature of the past decade (2010-2019) has been warmer than ever in the past 12,000 years.

“It is possible,” said Kaufman, “that the last time that the sustained global average temperature was 1 degree Celsius above the 19th century was before the last ice age, about 125,000 years ago when sea level was about 20 feet higher than today.” “”

The study is important because, by tracking global temperatures over the past 12,000 years, researchers can better predict future climate changes, scientists say.

“Our future climate will largely depend on the impact of human factors, particularly greenhouse gas emissions,” said study co-author Cody Routson, also an assistant professor at Northern Arizona University.

“However, the future climate will also be influenced by natural factors and made more difficult by the natural variability within the climate system. Future projections of climate change will be improved by taking better account of both anthropogenic (man-made) and natural factors.” “

The study was published in Nature Research’s Scientific Data, a journal.

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