UN says carbon levels at record high

Based on the current rate, the world's carbon dioxide pollution level is expected to cross the 400 ppm threshold by 2016, said WMO Secretary-General Michel Jarraud.

That is way beyond the 350 ppm that some scientists and environmental groups promote as a safe level and which was last seen in 1987.

Concentrations of CO2 build up over time because it stays in the atmosphere for decades. So even if emissions stopped today it would take many years before concentrations dropped significantly.

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