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Climate explained: what the world was like the last time carbon dioxide levels were at 400ppm
The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around four million years ago during a geological period known as the Pliocene Era (between 5.3 million and 2.6 million years ago).
The world was about 3℃ warmer and sea levels were higher than today.
- James Shulmeister
- The Conversation
We know how much carbon dioxide the atmosphere contained in the…