Carbon dioxide in the air at Mauna Loa

This is the concentration of carbon dioxide in the atmosphere, expressed in parts per million — the number of CO₂ molecules for every million molecules of dry air. Air is sampled continuously at the NOAA observatory on Mauna Loa, Hawaii, a high volcanic slope far from cities and forests, where the air is well mixed and broadly representative of the Northern Hemisphere. The record began in the late 1950s and is the longest direct measurement of its kind, underpinning much of what is known about human influence on climate. Values sit in the low 400s of ppm and rise by roughly 2 to 3 ppm each year, with a seasonal swing of several ppm as Northern Hemisphere plants absorb carbon in summer and release it in autumn. Daily figures are noisy, reflecting wind, local volcanic venting and vegetation, so trends emerge only over months and years.

Record high

433.95 ppm, 1 May 2026

Record low

326.06 ppm, 17 Sep 1974

First measurement

19 May 1974

Measurement cadence

daily

Measurements in this record

15,998