Kingston Images

A sealed glass flask preserves atmospheric carbon dioxide at 390.20 parts per million (ppm), collected at Mauna Loa Observatory in December 2010 during one of the final years before global CO₂ concentrations permanently surpassed the critical 400 ppm threshold. This unassuming scientific artifact, meticulously labeled with its precise carbon dioxide concentration, represents a pivotal moment in Earth's atmospheric history, capturing what scientists described as a "last gasp" of an atmospheric composition that had sustained human civilization for thousands of years. The 400 ppm mark serves as both a symbolic and scientific milestone—far exceeding the 350 ppm level many researchers consider the upper limit to avoid severe climate disruptions—with current measurements continuing their relentless climb, reaching a February 2025 monthly average of 427.09 ppm, an increase from 424.55 ppm just one year earlier. The Mauna Loa monitoring program, initiated by Charles David Keeling in the 1950s when CO₂ measured just 310 ppm, has transformed this modest flask into both a precise scientific record and a sobering time capsule of Earth's rapidly changing atmospheric chemistry.