That’s the current concentration of carbon dioxide found in the atmosphere over the Arctic, according to researchers from the National Oceanic and Atmospheric Administration (NOAA). Globally atmospheric carbon concentration has reached 395 ppm, up from 280 ppm before humans started burning fossil fuels in huge amounts following the Industrial Revolution, but the fast-warming Arctic is the first region to break the 400 ppm level. That’s worrying—the more carbon we add to the atmosphere, the faster the planet will likely warm. Many scientists believe that we need to keep carbon levels from rising above 450 ppm to avoid potentially catastrophic warming, while a smaller group of researchers led by NASA’s James Hansen believes the safe level may actually be as low as 350 ppm. As Jim Butler, the global monitoring director at NOAA, told the AP’s Seth Borenstein: “The fact that’s 400 is significant. It’s just a reminder to everybody that we haven’t fixed this and we’re still in trouble.”
On a day when the country is obsessing over the unemployment rate—up a tick to 8.2%—it’s also a reminder that they’re may be bigger numbers out there that aren’t scaring us enough.