less than a year after scientists first warned that the amount of carbon dioxide in the atmosphere could rise above 400 parts per million and stay there it has finally happened for the first time in recorded history the average level of co2 has topped 400 ppm for an entire monththe high levels of carbon dioxide is largely considered by scientists a key factor in global warming according to the national oceanic and atmospheric administration s noaa earth system research labince 1958 the keeling curve named after developer charles keeling has been used to monitor the levels of greenhouse gasses atop hawaii s mauna loa when keeling first started monitoring co2 levels the amount of carbon dioxide present in the atmosphere was 313 ppm