The background atmospheric carbon dioxide levels measured at Cape Grim on Tasmania’s northwest coast have officially passed the 400 parts per million (ppm) mark. Our measurements, compiled by our team at CSIRO together with the Bureau of Meteorology, show that the milestone was reached on May 10.

In the past few days, the 400 ppm level has also been breached in Antarctica, where CSIRO’s measurements at Casey Station show the 400 ppm level was exceeded on May 14.

Together, these measurements show that the atmospheric CO₂ concentration of the entire southern hemisphere is now at or above 400 ppm. It is unlikely to dip back below this level for many decades to come. Read More...