first time in human history, concentrations of carbon dioxide, the primary global warming pollutant, hit 400 parts per million in our planet's atmosphere

Yesterday, for the first time in human history, concentrations of carbon dioxide, the primary global warming pollutant, hit 400 parts per million in our planet’s atmosphere. This number is a reminder that for the last 150 years — and especially over the last several decades —...first time in human history, concentrations of carbon dioxide, the primary global warming pollutant, hit 400 parts per million in our planet's atmosphere