Phil Plait wrote 400: Another CO2 record high. "In May 2013, humans reached a new dark record: The daily level of carbon dioxide in the atmosphere, as measured at the Mauna Loa observatory in Hawaii, reached a value of 400 parts per million. That was the highest value recorded in human history...In April 2015, humans reached a new dark record: The monthly level of CO2 reached the 400 ppm mark. That’s no fluke, no brief spike. Its actually part of a very obvious long trend of an increase in the greenhouse gas in our atmosphere."
Scientists seem to suck at marketing. Skeptical Science wrote, Monthly global carbon dioxide tops 400ppm for first time. In that article, there's a section "Scientifically important or symbolic?" with six quotes all saying essentially: "Reaching 400 ppm doesn't mean much in itself, but the steady increase in atmospheric greenhouse gases should serve as a stark reminder of the task facing politicians as they sit down in Paris later this year."
Even Plait can only do as well as: "Carbon dioxide is a greenhouse gas, and the science on this is very basic, as basic as knowing a rock will fall when you drop it from your hand. At first blush 400 ppm may not sound like much, but it means we're significantly accelerating planetary heating. And warming the Earth doesn’t just mean we’ll be able to grow pineapples in Canada. It means huge changes to global weather patterns, changes we’re already seeing." and so he's going to.... VOTE!
That's all well and good and I'm all for voting, but this kind of language isn't going to convince anyone of anything. John Oliver should get on this and find the equivalent of "Can the NSA see my dick pics" to push this point.