The Keeling Curve is a graph of the annual variation and overall accumulation of carbon dioxide in the Earth's atmosphere based on continuous measurements taken at the Mauna Loa Observatory on the island of Hawaii from 1958 to the present day. The curve is named for the scientist Charles David Keeling, who started the monitoring program and supervised it until his death in 2005.
Keeling's measurements showed the first significant evidence of rapidly increasing carbon dioxide (CO2) levels in the atmosphere.
Background
Prior to the 1950s, measurements of atmospheric concentrations had been taken on an
ad hoc basis at a variety of locations. In 1938, engineer and amateur meteorologist Guy Stewart Callendar compared datasets of atmospheric from
Kew in 1898–1901, which averaged 274 parts per million by volume (ppm),
and from the eastern
United States in 1936–1938, which averaged 310 ppm, and concluded that concentrations were rising due to
Anthropogeny emissions.
However, Callendar's findings were not widely accepted by the scientific community due to the patchy nature of the measurements.
Charles David Keeling, of the Scripps Institution of Oceanography at UC San Diego, was the first person to make frequent regular measurements of atmospheric CO2 concentrations in Antarctica, and on Mauna Loa, Hawaii from March 1958 onwards.
Mauna Loa measurements
1957–1958, the International Geophysical Year, Keeling obtained funding from the
Weather Bureau to install infrared gas analyzers at remote locations, including the
South Pole and on the volcano of
Mauna Loa on the island of Hawaii.
Mauna Loa was chosen as a long-term monitoring site due to its remote location far from continents and its lack of vegetation. Keeling and his collaborators measured the incoming ocean breeze above the thermal inversion layer to minimize local contamination from volcanic vents.
The data was normalized to remove any influence from local contamination. Due to funding cuts in the mid-1960s, Keeling was forced to abandon continuous monitoring efforts at the South Pole, but he scraped together enough money to maintain operations at the Mauna Loa Observatory, which have continued to the present day.
Keeling's Tellus A article of 1960 presented the first monthly records from Mauna Loa and Antarctica (1957 to 1960), finding a "distinct seasonal cycle...and possibly, a worldwide rise in from year to year."
Carbon dioxide measurements at the Mauna Loa Observatory in Hawaii are made with a type of infrared spectrophotometer, now known as a nondispersive infrared sensor, that is calibrated using World Meteorological Organization standards.
Results and interpretation
The measurements collected at Mauna Loa Observatory show a steady increase in mean atmospheric CO
2 concentration from 313 parts per million by volume (ppm) in March 1958 to 406 ppm in November 2018,
with a current increase of 2.48 ± 0.26 (mean ± 2 std dev) ppm CO
2 per year.
This increase in atmospheric CO
2 is due to the
combustion of
, and has been accelerating in recent years. Since CO
2 is a
greenhouse gas, this has significant implications for
global warming. Measurements of CO
2 concentration in ancient
trapped in polar
show that mean atmospheric CO
2 concentration was between 275 and 285 ppm during the
Holocene epoch (9,000
Common Era onwards), but started rising sharply at the beginning of the nineteenth century.
The Keeling Curve also shows a cyclic variation of about 6 ppm each year corresponding to the seasonal change in uptake of by the world's land vegetation. Most of this vegetation is in the Northern Hemisphere where most of the land is located. From a maximum in May, the level decreases during the northern spring and summer as new plant growth takes out of the atmosphere through photosynthesis. After reaching a minimum in September, the level rises again in the northern fall and winter as plants and leaves die off and decay, releasing back into the atmosphere.
Legacy
Global monitoring
Due in part to the significance of Keeling's findings,
NOAA began monitoring CO
2 levels worldwide in the 1970s.
[Keeling, Charles D. (1978). "The Influence of Mauna Loa Observatory on the Development of Atmospheric CO2 Research". In Mauna Loa Observatory: A 20th Anniversary Report. (National Oceanic and Atmospheric Administration Special Report, September 1978), edited by John Miller, pp. 36–54. Boulder, CO: NOAA Environmental Research Laboratories.] Today, atmospheric CO
2 levels are monitored at about 100 sites around the globe through the Global Greenhouse Gas Reference Network.
Measurements at many other isolated sites have confirmed the long-term trend shown by the Keeling Curve,
[ Global Stations Concentration Trends. Scripps CO2 Program.] although no sites have as long a record as Mauna Loa.
Ralph Keeling
Since Charles David Keeling's death in 2005, responsibility and oversight of the project was transferred to Keeling's son,
Ralph Keeling. On the fiftieth anniversary of the beginning of the project, the younger Keeling wrote an article in Science magazine describing his father's life and work, along with how the project has grown and evolved over time.
Along with more precise measurement materials and funds for the project of monitoring of the Earth's levels, Keeling wrote about his pride for his father's work and how he has continued it in his memory.
Recognition
In 2015, the Keeling Curve was designated a National Historic Chemical Landmark by the American Chemical Society.
Commemorative plaques were installed at Mauna Loa Observatory and at the Scripps Institution of Oceanography at the University of California, San Diego.
Passing 400 ppm in 2013
On May 9, 2013, the daily mean concentration of in the atmosphere measured at Mauna Loa surpassed 400 parts per million (ppm).
Estimates of during previous
suggest that has not reached this level since the
Pliocene climate, 2 to 4 million years ago.
This level of carbon dioxide, causing
climate change, suggests a continued worsening in natural and ecological disasters, which increasingly threatens human and animal habitats on Earth, if greenhouse gas emissions are not significantly reduced.
See also
-
Greenhouse gas monitoring
-
Action for Climate Empowerment (ACE)
-
Paris Agreement
External links
