Please help
I may be a bit simple but the article in The Guardian has him saying:
"...when the world began to glaciate at the start of the Ice age about 35m years ago, the concentration of CO2 in the atmosphere stood at about 450ppm."
Then he says:
"If you leave us at 450ppm for long enough it will probably melt all the ice..."
Err... so it was at 450ppm when the ice formed but that same 450ppm is now enough to melt the ice. What is happening?


