Con

Earth’s climate has always warmed and cooled, and the 20th century rise in global temperature is within the bounds of natural temperature fluctuations over the past 3,000 years.

Although the planet has warmed 1-1.4°F over the 20th century, it is within the +/- 5°F range of the past 3,000 years. [114] A study by researchers at the Harvard-Smithsonian Center for Astrophysics found that “many records reveal that the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millennium.” [115]

A study published in Nature found that “high temperatures – similar to those observed in the twentieth century before 1990 – occurred around AD 1000 to 1100” in the Northern Hemisphere. [116] A study published in Boreas found that summer temperatures during the Roman Empire and Medieval periods were “consistently higher” than temperatures during the 20th century. [59]

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