What Human Greenhouse Gases Are Doing

Humans Have Caused the Most Dramatic Climate Change in 3 Million Years

Stephanie Pappas, April 3, 2019 (LiveScience)

“The level of carbon dioxide in the atmosphere today is likely higher than it has been anytime in the past 3 million years…[and] could bring temperatures not seen over that entire timespan…[Computer modeling of the Quaternary period, which started around 2.59 million years ago and continues into today, show] Earth has undergone a number of changes, but none so rapid as those seen today…[The Quaternary period began with a period of glaciation, but] between 1.25 million and 0.7 million years ago, these glacial and interglacial cycles stretched out, re-occurring every 100,000 years or so, a phenomenon called the mid-Pleistocene transition…[It was apparently caused by volcanic and weathering changes that led to carbon dioxide declines and] less heat being trapped…

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[The climate would have cooled to the point where large ice sheets could form more easily… These resilient ice sheets, plus a cooler climate, resulted in the longer glacial cycles seen after about a million years ago…[The modeling] suggests that carbon dioxide was below 400 parts per million for the entire Quaternary period. Today, the global average is 405 parts per million and rising…[Around 2.5 million years ago, average global temperatures were temporarily about 2.7 degrees Fahrenheit (1.5 degree Celsius) higher than average before the widespread use of fossil fuels…[But] the globe is 2.1 degrees F (1.2 degrees C) warmer than the pre-industrial average…” click here for more

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