Mauna Loa Observatory

Mauna Loa Observatory is designed to sample background air that is relatively representative of the remote atmosphere over the central Pacific. The station stands at about 3,397 metres on the northern slope of Mauna Loa, well above most of Hawaii's local boundary layer and far from major industrial sources.¹ NOAA operates it as part of the Global Monitoring Laboratory's worldwide network, which combines surface stations, aircraft, balloons, ships, and satellites.

The high elevation is scientifically valuable but does not make every measurement automatically global. Local winds, nearby vegetation, human activity, and volcanic emissions can briefly affect the air arriving at the instruments. Researchers identify and filter such episodes when constructing background records, while retaining observations that reveal atmospheric transport and volcanic processes.

The observatory's best-known achievement is its atmospheric carbon-dioxide series, which made the seasonal breathing of the biosphere and the long-term rise caused mainly by fossil-fuel combustion visible in a single record.² Charles David Keeling of Scripps Institution of Oceanography began measurements at Mauna Loa in 1958; NOAA later developed an independent program, allowing the two records to serve as important comparisons.

CO₂ concentrations rise during much of the Northern Hemisphere winter as plant respiration and decay exceed photosynthetic uptake, then fall during the growing season. The annual oscillation is superimposed on a persistent upward trend. The record is not a measure of emissions at the volcano or on the island: it is an atmospheric concentration series used with observations from other locations, inventories, and carbon-cycle models.

Mauna Loa Observatory measures much more than carbon dioxide. Its programs include other greenhouse gases, ozone, solar and infrared radiation, aerosols, water vapour, meteorological variables, and selected trace gases important to atmospheric chemistry.¹ These observations support detection of long-term climate change, evaluation of atmospheric models, estimates of radiative forcing, and international assessments of greenhouse-gas trends.

Long-term continuity is central to the station's value: a consistent instrument record can reveal gradual changes that short campaigns would miss. The data also provide a high-altitude reference for distinguishing regional pollution from broader atmospheric signals. NOAA's measurements are compared with the Scripps record and with stations elsewhere, including remote marine and polar sites, before being interpreted as evidence of global change.³

Mauna Loa's isolation creates both an advantage and a complication. Air can arrive from the free troposphere over the Pacific, but downslope and upslope winds can carry local air to the station; analysts therefore classify observations by wind direction and other conditions.¹ The observatory also sits on an active shield volcano, so eruptions and sulfur-rich volcanic plumes can interrupt access or contaminate measurements.

The 2022 eruption of Mauna Loa temporarily affected roads, power, and operations, illustrating how a globally important climate record depends on a remote mountain site. The broader lesson is that the Keeling Curve is not produced by one sensor alone: calibration, quality control, parallel observations, and a distributed observing network turn local samples into a durable climate record.²

Keeling Curve

The long-term record of atmospheric carbon-dioxide concentration associated especially with measurements begun by Charles David Keeling at Mauna Loa in 1958.

Background air

Air whose composition is relatively representative of a broad region rather than dominated by nearby local emissions.

Free troposphere

The part of the troposphere above the atmospheric boundary layer, where air is less directly influenced by the surface.

Global Monitoring Laboratory

The NOAA laboratory responsible for observing atmospheric composition and related environmental variables worldwide.