Keeling Curve
The Keeling curve is the graph of global mean concentration profile of the trace gas carbon dioxide ( CO2) in the atmosphere since 1958. It is named after Charles David Keeling of the Scripps Institution of Oceanography. This was the first to show that the concentration of the greenhouse gas increases through land use change and fossil fuel combustion. The curve shows a characteristic fluctuating course of the year, as the concentration increases in the air in spring and in autumn from.
The Keeling curve has a great importance, as it is considered important evidence for the in the history of science of global warming - was man-made global warming - which then formulated only as a theory. From the measured data as well as the curve significant scientific findings can be summarized.
Charles Kennel honored in 2005 Keeling scientific achievements with the words: " Charles David Keeling messtechischer evidence of the global increase in atmospheric carbon dioxide concentration were the starting point for today's major concerns because of global warming, it is the most important record of the twentieth century in view. on environmental impact. "
- 3.1 Early Results
- 3.2 Results from the long-term analysis of the measurement series
Prehistory
Both Guy Stewart Callendar (1937 ) and Gilbert Plass (1956 ) supported by new, more accurate calculations, first formulated in 1895 by Svante Arrhenius theory of global warming by one resulting from the burning of fossil fuels rise in atmospheric CO2 concentration. However there was no proof of an increase in concentration, nor was known at the time the amount of remaining carbon dioxide in the atmosphere. Neither knew the type and speed, with the mixed up ocean waters.
Since the 19th century, repeated attempts to determine the atmospheric carbon dioxide content, however, the results varied so much that was adopted by the majority of researchers, an accurate measurement was not possible. Even in 1954 a group of researchers tried to Stig Fonselius, with the help of 16 stations installed in Scandinavia, to determine the atmospheric CO2 concentration. The project was soon abandoned because the measurement results thus strongly differed from each other, that is no system was apparent. Many scientists therefore assumed that CO2 concentrations varied greatly from place to place, a " background concentration " did not exist and all by man by combustion gas volumes would be absorbed by the oceans.
The then head of the Scripps Institute, Roger Revelle, was an expert in the chemistry of the oceans. He also did not know how fast and in what quantity additionally introduced by humans, atmospheric CO2 would be released into the sea. In the 50s, Revelle became aware of the research results of Hans E. Suess. He tried to improve the accuracy of radiocarbon dating and discovered in 1955, named after him Suess effect. The Suess effect could only be explained by the fact that carbon dioxide, which came from the burning of fossil fuels, accumulate in the atmosphere. Revelle saw in the evaluation of nuclear weapons effect a way to determine the proportion of the captured carbon dioxide from the oceans to determine in this way one may be held concentration increase of the greenhouse gas. He also wanted to gain new insights about the mixing of the oceans; the two worked together from then on. After evaluation of the 14C measurements calculated Revelle that of incorporated of carbon dioxide into the atmosphere, only 20% would solve in the sea. An increase in concentration in the atmosphere that is should be possible to demonstrate by measurement.
As a post-doctoral researcher developed and perfected Charles Keeling in 1953 measuring arrangements with which he examined the CO2 equilibrium concentrations between the atmosphere, limestone and surface waters. He led with the help of aircraft, weather balloons and ships by the first measurements. In Pasadena he noticed the regionally highly fluctuating gas concentrations; in a wooded area of Big Sur showed the atmospheric CO2 concentration in the diurnal variation of strong fluctuations. The air contained at night more and more CO2 than during the day, in the afternoon, however, always about 310 ppm.
In contrast to the group to Fonselius Keeling postulated due to its acquired data that the atmospheric CO2 concentration should be far away from interfering sources and sinks largely constant. In 1956, he beat Harry Wexler of the U.S. Weather Bureau (now National Weather Service ) and Roger Revelle of the Scripps Institution of Oceanography, a global measurement program before. As Revelle and Suess were also interested in accurate CO2 measurements, the Sripps Institute finally successfully applied for the International Geophysical Year in 1957/58 with the measurement program large-scale, and Keeling was entrusted with the management of the project.
The measurements
With the additional financial support Keeling able to obtain 4 gas analyzers, and he established in 1958 located on the Hawaiian volcano Mauna Loa, the first measuring station. There he began in March 1958, systematic measurements of the greenhouse gas carbon dioxide. The remaining three gas analyzers he placed in the Antarctic, in California and in his laboratory. With the latter instrument he evaluated at different locations collected samples from, for example, were obtained with the aid of airplanes. The first, used for subsequent Keeling curve measured value was 313 ppm CO2.
In 1948 published book by Kurt measurements indicate typical concentrations of the greenhouse gas ranged from 150-230 ppm ( Arctic) and 319-349 ppm ( tropics). The Keeling first published in 1962 values were significantly more accurate. He gave for the Arctic a range 313-325 ppm and for the equatorial Pacific a range of 317-321 ppm. Previous measurements were based on wet chemical methods, while Keeling used a precisely measured non-dispersive infrared sensor and eliminated the disruptive effect of changing humidity. The measurement uncertainty of his trial was Keeling in 1960 with / - 0.3 ppm, which he later by a possible re-calibration to / - 0.1 ppm could increase even further.
Disorders of measurement results
In contrast to the recently failed project in Scandinavia metering stations of Keeling away disturbing carbon dioxide sources were placed. Thus, the station had been set up on Mauna Loa at high altitude on the windward side. The station in Antarctica was far away from CO2 sources and sinks. Nevertheless, were sometimes distorted at all measurement locations from the outset identified carbon dioxide concentrations by impurities. At the South Pole, an internal combustion engine, for example, was once the cause, which ran close to the station. At Mauna Loa, these were outgassing of the volcano, which could reach in rare cases up to the station. However, the disturbances were always clearly visible in the records, because they were of short duration and high amplitude, so that these values could be detected and discarded easily.
Results and impact
Keeling's measurements laid the foundation for further measurements of other atmospheric gases. Scientists were excited by Keeling's successes, to determine the concentration profiles of the greenhouse gases methane and nitrous oxide and measurements of ozone concentration were initiated. Nevertheless, the measurement program was threatened repeatedly and multiple continuous measurements should be adjusted, as has been argued that random measurements would show the same results as continuous measurements.
Early results
In the first months of his measurements Keeling doubted whether his theory of a background concentration could be correct because the values rose for several months, only to fall. However, since he did not give up and the measurements ran for several years, he was able to show that the fluctuations had an annual period, which he attributed to the seasonally changing growth period of vegetation. In the northern hemisphere, with their greater land area, are significantly more plants than in the southern hemisphere. During northern spring therefore more CO2 from the atmosphere than during the northern autumn, when south of the Equator, the strongest growth occurs.
After a few years it became apparent that the measured values from year to year increase. Keeling was able to prove by measurement that the atmospheric carbon dioxide concentration is increasing from year to year and thus support the theory of a possible man-made global warming by Svante Arrhenius. The measured increase in concentration corresponded almost exactly to the expected values by burning fossil fuels.
Keeling's measurements also included the determination of the isotopic ratios 13C/12C. He was able to prove the influence of land plants on the Kohlenstoffdioxidkonzentrationsverläufe by isotope studies, because land plants preferentially take the lighter 12C. The ratio was lower than during the day and at night during the year showed a similar pattern. He published these results already in 1960 in the journal Tellus.
Results from the long-term analysis of the measurement series
Since Keeling managed to maintain the continuity of measurements, analyzes of the time courses for several years and decades were possible.
Mid-1970s was the accuracy of the measurement series large enough in order to determine the proportion of anthropogenic CO2 emissions remaining in the atmosphere and is not absorbed by the oceans: the value is 57%.
Mid-1990s, was identified by accurate determination of the rise and fall of the curves that spring - due to global warming - to the Northern Hemisphere by about a week earlier than began at the beginning of the measurement series.
Through long- term monitoring of the concentration trend of atmospheric 13CO2 and molecular oxygen, the burning of fossil fuels could be positively identified as the main source for the observed strong increase in the concentration of the greenhouse gas carbon dioxide.
The comparison between the equatorial CO2 concentrations with the data obtained in Arctic latitudes showed the seasonal influence of the growth period: During the annual course of the curves äquatornah is only about 3 ppm, it lies in Arctic latitudes at 20 ppm. The annual amplitude of this oscillation has also compared to the experiences of the 1960s curves by 20 % (Hawaii ) or 40% ( Arctic region ) increased the mid-1990s. Keeling suspected that this was due to an increased assimilation of land plants that respond to the increased CO2 supply and the rise in temperatures with increased growth.
Depending on the sea surface temperature varies, the CO2 absorption capacity of sea water; Henry's law constant is strongly temperature dependent and for carbon dioxide; cold water can solve the trace gas well, but in warm water, it is only sparingly soluble. El Niño and La Niña affect the surface temperature of the Pacific Ocean over a large area. Years less CO2 uptake of the oceans could be correlated with El Niño events.
As of today
With the exception of an interruption in 1964, the data from Mauna Loa are to this day before in an unbroken series. The measurement had to be suspended due to a short-term non-recoverable equipment defect at the time.
During the last 800,000 years, the concentration of carbon dioxide in the atmosphere has never been greater than 300 ppm. In the 750 years 1000-1750 AD, the amount of CO2 in the atmosphere was 275-285 ppm. Increased by 50 ppm over a period of 200 years was observed in 1970. An increase by a further 50 ppm was only 30 years later. Fraud, the annual rate of increase between the years 1959 and 1969 on average 0.86 ppm, as she lay in the period between 2000 and 2010 at an average of 2.01 ppm. Lag of CO2 in the atmosphere in the early 1950s still at about 310 ppm, he has risen to 390 ppm in 2011.
The Scripps Institute operates besides the active to the present day station in Hawaii more plants, etc. in Alert ( Nunavut ), Barrow ( Alaska), the Trinidad Head Observatory ( California), on Tutuila (American Samoa) and the South Pole. NOAA takes over 60 stations twice a week samples. Worldwide samples were in 2008 to 282, taken mostly to Europe and the United States belong areas. Since 2009, the regional distribution of greenhouse gas concentrations also from space is detected by the satellite GOSAT.
The monitoring of the measurement series in Hawaii by the late Charles Keeling began in 2005, were taken over by his son, Ralph F. Keeling, who is a professor of oceanography and also the measuring range was extended to include the atmospheric oxygen content.
In the spring of 2013, the CO2 concentration at the monitoring station at Mauna Loa exceeded the value of 400 ppm for the first time.