The cleanest air on Earth
Located at 3,397 meters (11,135 feet) on the northern flank of a massive volcano, the Mauna Loa Observatory samples some of the purest air on the planet. Its location is far from industrial centers and, importantly, it sits above the marine inversion layer—a stable atmospheric zone that separates the polluted lower air from the clean, well-mixed air of the free troposphere. This unique positioning allows for the collection of atmospheric data with minimal local contamination.
The observatory's most famous work began in March 1958, when scientist Charles David Keeling started a continuous monitoring program for atmospheric carbon dioxide. His first measurement registered 313 parts per million (ppm). Keeling’s meticulous data collection soon revealed two patterns. First, a steady year-over-year increase in overall CO₂ concentration. Second, a seasonal "sawtooth" cycle. CO₂ levels drop during the Northern Hemisphere's spring and summer as extensive plant life absorbs the gas, and rise in the fall and winter as that vegetation decays. This rhythmic fluctuation is called the "breathing" of the planet.
The resulting graph of these measurements is the Keeling Curve. It provided the first unambiguous evidence that human activities, primarily the burning of fossil fuels, were causing atmospheric CO₂ to accumulate. Today, both the Scripps Institution of Oceanography and the National Oceanic and Atmospheric Administration (NOAA) maintain parallel CO₂ measurement programs at the site.
A record under threat
For over six decades, the data collection at Mauna Loa continued almost without interruption. That changed on November 27, 2022, when Mauna Loa erupted for the first time in 38 years. Lava flows buried the access road and severed the observatory's power lines, forcing a pause in all measurements.
To maintain the continuity of this important dataset, scientists from NOAA and Scripps quickly established a temporary measurement site on the nearby volcano of Maunakea. The Scripps program resumed measurements at Mauna Loa on March 9, 2023, using a solar power and battery system installed via helicopter. By May 2024, the monthly average CO₂ concentration at Mauna Loa reached a new record of nearly 427 ppm, a level over 50% higher than pre-industrial times.
The observatory does measure carbon dioxide. Its mission includes monitoring a wide range of atmospheric constituents, including methane, carbon monoxide, nitrous oxide, and ozone. Data from Mauna Loa is also used to calibrate instruments on global satellites. Despite its proximity to a volcano, careful analysis allows scientists to easily filter out any readings contaminated by local volcanic vents, ensuring the integrity of the long-term global record.