Press release from September 28th, 2011
Productivity of land plants may be greater than previously thought
Researchers recommend the reworking of global carbon models in NATURE
London. The global uptake of carbon by land plants may be up to 45 per cent more than previously thought. This is the conclusion of an international team of scientists, based on the variability of heavy oxygen atoms in the carbon dioxide of the atmosphere driven by the El Niño effect. As the oxygen atoms in carbon dioxide were converted faster than expected during the El Niño years, current estimates for the uptake of carbon by plants are probably too low. These should be corrected upwards, say the researchers in the current issue of the scientific journal NATURE. Instead of 120 petagrams of carbon, the annual global vegetation uptake probably lies between 150 and 175 petagrams of carbon. This value is a kind of gross national product for land plants and indicates how productive the biosphere of the Earth is. The reworking of this so-called global primary productivity would have significant consequences for the coupled carbon cycle-climate model used in climate research to predict future climate change.
Lisa Welp of the Scripps Institution of Oceanography at the University of California in San Diego and her colleagues evaluated the data for the global isotopic composition of the greenhouse gas CO2 over the last 30 years. This analysis indicated regular fluctuations between years and a connection with the El Niño phenomenon in the Pacific. Overall, El Niño years are warmer. They are also characterised by greater precipitation in South America and less intensive monsoons in Southeast Asia. The researchers found a more rapid recovery of the isotopic ratios following the El Niño events than assumed, indicating a shorter conversion time for CO2 in the terrestrial biosphere. On the basis of these data, the authors calculate the so-called global primary productivity (GPP). They now propose correcting this in the global models from 120 to 150-175 petagrams*) of carbon annually.
Since 1977 the isotopic ratios in the carbon dioxide of the atmosphere (18O/16O und 13C/12C) have been measured in order to better understand the global carbon cycle, as the exchange processes between the biosphere, the atmosphere and the oceans are reflected in these values. "We assume that the redistribution of moisture and rain in the tropics during El Niño raises the 18O/16O ratio in precipitation and plant water and then signals this to the atmospheric carbon dioxide", explains Lisa Welp the new approach of the researchers.
"Our atmosphere is a perfect blender. Changes in its levels of trace gases - such as carbon dioxide - reflect the overall release and uptake of trace gases from all sources. So if you measure the carbon exchange of a forest ecosystem, for example, you "only" get the net exchange of all the carbon taken up by the trees for photosynthesis and all the carbon released by the trees and soil ", writes Dr. Matthias Cuntz of the Helmholtz Centre for Environmental Research (UFZ) in his commentary in the same issue of NATURE. The gross-exchange fluxes, such as photosynthesis, are however accessible only with difficulty. "Global estimates therefore depend upon a number of assumptions. This includes, for example, how many of the CO2 molecules entering a plant are actually fixed by photosynthesis. The researchers of Lisa Welp's team assume that around 43 per cent of all CO2 molecules entering a plant are taken up by the plant. If this were only 34%, the estimate would fall to about 120 billion tons of carbon - that is, to the currently accepted value", for Matthias Cuntz reason of thought. In his opinion, the new findings do not completely upset the research to date. Nevertheless, they demonstrate an interesting new method for the determination of plant productivity over large areas. In future, the combination of several isotopic methods with conventional measurements represents a promising approach.
The now published study was carried out under the direction of Ralph F. Keeling, a professor of oceanography and the son of the late Charles David Keeling, after whom the so-called Keeling curve was named.
This graph shows the concentration of CO2 of the volcano Mauna Loa on Hawaii since the year 1957. In the 1950s the CO2 fraction in the earth's atmosphere was still around 315 ppm.
In 2011, by comparison, it has already increased to 390 ppm. With his measurements Keeling was able to show for the first time that the concentration of the greenhouse gas increases in relation to changing
land use and the combustion of fossil fuels. This new study underscores the importance of long-term measurements of the isotope 18O in the carbon dioxide of the atmosphere from the scientific point of
view, as this occupies a key position between the carbon cycle and the hydrogen cycle.
With its expertise the UFZ contributes to climatic change research and the development of strategies for adaptation. Thus, for example, the UFZ is responsible for the scientific monitoring, coordination and synthesis (GLUES) in Module A of the Federal Ministry of Education and Research (BMBF) priority research project "Sustainable Land Management", results of which will be presented at the UN Climate Conference at the end of November in Durban. The UFZ climate economist Professor Reimund Schwarze will report on the status of negotiations from Durban (http://blog.ufz.de/klimawandel).
Lisa R. Welp, Ralph F. Keeling, Harro A. J. Meijer, Alane F. Bollenbacher, Stephen C. Piper, KeiYoshimura, Roger J. Francey, Colin E. Allison & Martin Wahlen (2011):
Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Niño.
29 September 2011, Vol. 477, Nature 579, 579-582. doi:10.1038/nature10421
Matthias Cuntz (2011): A dent in carbon´s gold standard.
29 September 2011, Vol. 477, Nature 579, 547-548.
Lisa Welp (primary author of the study)
University of California, San Diego, La Jolla, CA, USA
Tel: +1 858 822 1642
Helmholtz Centre for Environmental Research (UFZ)
Tel.: +49 341 235-1635
CO2- and Isotopic Measurement Program of the Scripps Institution of Oceanography, USA::
Atmospheric Measurement Program of the National Oceanic & Atmospheric Administration, USA:
Cape Grim Baseline Air Pollution Station, Tasmania, Australia:
El Niño - Southern Oscillation (ENSO):
In the Helmholtz Centre for Environmental Research (UFZ) scientists are researching the causes and consequences of far-reaching changes to the environment. They are concerned with water resources, biological diversity, the consequences of climate change and adaptability, environmental and biotechnologies, bioenergy, the behaviour of chemicals in the environment, their effect on health, modelling and social science issues. Their guiding theme: Our research contributes to the sustainable use of natural resources and helps to secure this basis for life for the long term under the effects of global change. The UFZ employs 1,000 people in Leipzig, Halle and Magdeburg. It is financed by the federal government and the federal states of Saxony and Saxony-Anhalt.
The Helmholtz Association contributes towards solving major and pressing social, scientific and economic issues with scientific excellence in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter and Aeronautics, and Space and Transport. The Helmholtz Association is Germany’s largest scientific organisation with over 31,000 employees in 17 research centres and an annual budget of approximately 3 billion euros. Its work stands in the tradition of the naturalist Hermann von Helmholtz (1821-1894).