Warmist Damian Carrington claims that 400ppm of CO2 will eventually cause the Arctic to be ice-free and sea level to rise 40 meters?

Open door: The readers' editor on... when unattributed facts need backing up | Comment is free | The Guardian

While making clear that he is not a climate change sceptic, Lipsey takes issue with the way the concentration of carbon dioxide passing 400 parts per million (ppm) was reported. In the first sentence the event is described as a "milestone". The story goes on to say that the last time so much greenhouse gas was in the air "the Arctic was ice-free, savannah spread across the Sahara desert and the sea level was up to 40 metres higher. "These conditions are expected to return in time…"
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Damian Carrington, the Guardian's head of environment, wrote the story. He said:
• "It's a 'milestone' because it is a round number
• 'expected to return in time' - this is completely uncontroversial among climate scientists – the last time we had 400ppm CO², both temperature and sea level was far higher, but it takes time for the planet to adjust