Climate change may have reached the point of no return last month.
CO2 levels in the atmosphere topped 400 parts per million on May 19, for the first time since the Pleistocene era, over 2.5 million years ago. President Barack Obama’s historic speech on climate change today highlights his growing focus on this issue for his second term.
Climate scientists have long regarded that 400 number as the symbolic threshold. One step beyond, and it would be virtually impossible to put the brake on human-generated climate change. The bad news escalated last week when the International Energy Agency reported that global emissions of carbon dioxide rose 1.4 percent in 2012, the largest annual increase on record.