Scharpenseel und Becker-Heidmann 1993

Scharpenseel, H.-W., Becker-Heidmann, P. (1993): The dilemma of conflicting interests between CO2‘s and CH4‘s IR trapping capacity and role, in case of CO2 even as limiting factor, for plant growth. – In: Institute for World Resource Research (Hg.): World Resource Review, S. 242–258. World Resource Review 4,2

Abstract:

– The first dilemma is that CO2, being responsible for ca 50% of anthropogenic „greenhouse forcing“, is at the same time, despite rising from 200 ppm at the end of the last glacial via 280 ppm at the beginning of industrialization to 350 ppm by now, still suboptimal for plant growth and highest crop yields. C3 plants, comprising ca 2/3 of major crops, would gain ca 30% in biomass production and 30% in water economy (provided the other growth factors like nutrients are alright), C4 plants show ca 10% biomass increment and the same advantage as C3 in water economy by doubling of the atmospheric CO2 concentration.
– The second dilemma is the need of doubling food production within the next 30 years, concomitant with the doubling world population, and that seems achievable only by mobilizing all natural and technical resources, may be including rise of CO2.
– A third dilemma is the back lash of other major plant growth promoters, like N-fertilization or expanding irrigation to enhancing the greenhouse effect by rising N2O and CH4 emissions (efficiency factors per molecule for  N2O = 150, for CH4 = 32, compared to CO2), besides of consuming about 1 l of oil for production of 1 kg N-fertilizer.
– A fourth one is showing the urgency of all including decisions and for initiating strategic research to fill identified gaps of knowledge, like carbon source – sink relations in soil – plant systems of different climate belts at rising CO2 concentration, CO2-source <-> CO2-fertilization <-> CO2-sequestration <-> CO2-sink relations. It relates to the short period for doubling food production in adherence to the trend of population growth, while the CO2 residence time and all what we decide now wih CO2 covers ca 100 years, about three times as long (CH4 with 10 years residence time but 1/3). At first glance the best solution seems curtailing CO2 emission and being ready to allow an increase, if for more food production it may become imperative. But, if once CO2 emission is down due to harsh, costly and painful legal interventions, the new established pattern of reduced fuel consumption would not allow any more just to open the CO2 tap for more biomass production and adjust it to the right aperture. Thus, decisions must be taken as early as sufficient knowledge allows them to be qualified.
– And a further fifth dilemma is that we only hesitantly accept, f.ex. from ice cube gas analysis and sedimentation measurements, that variability in CO2 concentration, temperature, precipitations and eustatic sea level rise has always been considerable, and that the greatest actual danger is probably existing for the historically based concentration of precious human settlements, factories and transport routes in alluvial plains and near the sea shore, i.e. due to former and still ongoing anthropogenic decisions, that basically allow despite of gigantic problems at least as much flexibility as we can afford in facing the world food supply problems.
– It could be easily the greatest dilemma at all, if policy decisions regarding CO2 and other IR trapping gases would come under the biased influence of lobby presentations, be it solely the atmospheric chemistry point of view or too dominantly land use/food supply doomsday predictions, instead of bringing protection of climate and of world nutrition on a very high policy level together for unbiased component technological treatment and decisions after thorough weighing of the diverse arguments.

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