A companion piece about crossing the 400 ppm boundary, also from the southern hemisphere: http://www.sciencemag.org/news/2016/05/atmospheric-carbon-dioxide-soar

A companion piece about crossing the 400 ppm boundary, also from the southern hemisphere: http://www.sciencemag.org/news/2016/05/atmospheric-carbon-dioxide-soars-past-crucial-milestone http://www.sciencemag.org/news/2016/05/atmospheric-carbon-di...