NOAA reported that six other arctic monitoring stations in their international cooperative air sampling network have reported CO2 concentrations of 400 ppm this spring. These measurements from remote high latitude stations in Alaska, Canada, Iceland, Finland, Norway and the North Pacific reflect background levels of CO2 influenced by the long-term trend of increased human emissions, as opposed to measurements of more direct emissions near population centers. NOAA’s Cape May, New Jersey station has exceeded 400 ppm in the spring for several years. Atmospheric carbon dioxide concentrations run through a natural annual cycle, rising in the fall, winter, and early spring as plant material decays and releases its carbon. Concentrations fall as plant growth takes the CO2 back up in the late spring and summer. The Arctic region continues to serve as the global climate \"canary in a coal\" mine. Now, as with average temperature rise, the region is leading into a new troubling milestone as monitoring stations near a remote outpost near Barrow, Alaska are among several such stations to report that average concentrations of CO2 have reached an average of 400 parts per million (PPM) this spring. \"The northern sites in our monitoring network tell us what is coming soon to the globe as a whole,\" reports atmospheric scientist Pieter Tans with the National Oceanic and Atmospheric Association (NOAA). \"We will likely see global average CO2 concentrations reach 400 ppm about 2016.\"