There's striking new evidence that Earth's atmosphere is increasingly saturated with carbon dioxide, the major gas from fossil fuel emissions that trigger climate change.
Measurements of the climate-changing gas by instruments high on a mountain in Hawaii and around the world show that global emissions from burning fossil fuels rose last month to levels higher than at any time in human history - and higher than it has been in hundreds of thousands of years.
"This should be taken as a warning," said Ken Caldeira, an atmospheric scientist with the Carnegie Institution's department of global ecology at Stanford University. "It is time to stop building things with tailpipes and smokestacks.
"It is time to stop using the sky as a waste dump for our carbon dioxide pollution. If we fail to heed this warning, our children will end up living in a world that is much hotter than any human being has ever experienced."