On May 9, the daily mean concentration of carbon dioxide (CO2) in the atmosphere of Mauna Loa, Hawaii, surpassed 400 parts per million (ppm) for the first time since measurements began in 1958. Mauna Loa is the oldest continuous carbon dioxide measurement site in the world and serves as the primary global benchmark site.
Back in 1958, Charles David (Dave) Keeling, a world-leading authority on atmospheric greenhouse gas accumulation and Scripps climate science pioneer of the Scripps Institution of Oceanography began measuring carbon dioxide at the observatory near the summit of Mauna Loa. At an altitude of 3400 m, the location is well situated to measure air masses that are representative of very large areas. The record of CO2 measured at Hawaii’s Mauna Loa became known as the “Keeling Curve.”
These iconic measurements comprise the longest continuous record of CO2 in the world, starting from 316 ppm in March 1958 and approaching 400 ppm today. For the past 800,000 years, CO2 levels never exceeded 300 parts per million. Each year, the concentration of CO2 at Mauna Loa rises and falls in a sawtooth fashion, with the next year higher than the year before.
Carbon dioxide is the most significant heat-trapping greenhouse gas contributing to climate change. Its concentration has increased every year since scientists started making measurements on the slopes of Mauna Loa more than five decades ago.
The rate of increase has accelerated since the measurements started, from about 0.7 ppm per year in the late 1950s to 2.1 ppm per year during the last 10 years.Before the Industrial Revolution in the 19th century, global average CO2 was about 280 ppm. During the last 800,000 years, CO2 fluctuated between about 180 ppm during ice ages and 280 ppm during interglacial warm periods. Today’s rate of increase is more than 100 times faster than the increase that occurred when the last ice age ended.
The website keelingcurve.ucsd.edu offers background information about how CO2 is measured, the history of the Keeling Curve, and resources from other organizations on the current state of climate. On Twitter, @keeling_curve, also provides followers with the most recent Keeling Curve CO2 reading in a daily tweet.
The Scripps CO2 measurements at Mauna Loa have been supported for many years by the U.S. Department of Energy, and have more recently been supplemented by Earth Networks, Inc., which is partnering with Scripps to expand the global GHG monitoring network.
- NOAA carbon dioxide data: http://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html
- Scripps Institution of Oceanography carbon dioxide data: http://www.keelingcurve.ucsd.edu/
- NOAA’s Maua Loa Observatory: http://www.esrl.noaa.gov/gmd/obop/mlo/
- ANIMATION (carbon dioxide levels over 800,000 years): http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html
- IMAGES: http://www.esrl.noaa.gov/gmd/Photo_Gallery/Field_Sites/MLO/