The amount of heat-trapping carbon dioxide in the atmosphere has shot past a key milestone -- more than 50% higher than pre-industrial times -- and is at levels not seen since millions of years ago when Earth was a hothouse ocean-inundated planet, federal scientists announced Friday.
The National Oceanic and Atmospheric Administration said its long-time monitoring station at Mauna Loa, Hawaii, averaged 421 parts per million of carbon dioxide for the month of May, which is when the crucial greenhouse gas hits its yearly high. Before the industrial revolution in the late 19th century carbon dioxide levels were at 280 parts per million, scientists said, so humans have significantly changed the atmosphere. Some activists and scientists want a level of 350 parts per million. Industrial carbon dioxide emissions come from the burning of coal, oil and gas.
