Many of the worlds leading scientists now say that the safe upper limit for atmospheric CO2 is 350 ppm (parts per million). Our atmosphere is currently at 386.92 ppm - up from 310 ppm fifty years ago and 280 ppm a century ago. This trend urgently needs to be reversed or we'll be cooked - literally.
An organization called 350.org has created a very cool little video to communicate this concept in 90 seconds with zero words. Worth watching.