CO2 Levels Already Topped 400 ppm This Year, on Track to Cross Threshold for a Month

Last year, atmospheric carbon dioxide briefly crossed 400 parts per million for the first time in human history.  However, it didn’t cross that threshold until mid-May.  This year’s first 400 ppm reading came a full two months earlier this past week, and the seeming inexorable upward march is likely to race past another milestone next month.

“We’re already seeing values over 400.  Probably we’ll see values dwelling over 400 in April and May.  It’s just a matter of time before it stays over 400 forever,” said Ralph Keeling in a blog post.

While 400 ppm is mostly a symbolic number, the climate changes it could cause are not. Among other impacts, increased carbon dioxide contributes to heating the planet’s surface and ocean temperatures, which in turn melts ice and raises ocean levels.

CO2 on Path to Cross 400 ppm Threshold for a Month