El Niño Has Pushed Our Climate Past A Major Climate Milestone - gizmodo.com

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"... study published today in Nature Climate Change finds that 2016 is now on track for an atmospheric average of 404.45 plus or minus 0.53 ppm. In other words, it’ll be the first year in the history of our species that we can truly say we’ve been living in a 400 ppm world."

"For instance, the last time the Earth was a 400 ppm world—the mid-Pliocene—sea levels were an estimated 50 to 80 feet higher than they are today, meaning Florida, much of the Gulf Coast, and countless other coastlines worldwide did not exist in their current form."