Formel falsch: In Bäumen ist weniger Kohlenstoff enthalten als gedacht

Klimaklamauk von Eugene Chan im Journal of Environmental Psychology:

Climate change is the world’s greatest threat – In Celsius or Fahrenheit?
In two experiments, participants who were told that the Earth’s average temperature was −24 °C thought that it was more important to limit climate change than those who were told that it was −16 °C. However, participants who were told that the average temperature was −11 °F thought it was less important to reduce the carbon footprint than those who were told that it was 3 °F. The findings contradict each other since −24 °C is the same as −11 °F, and −16 °C is the same as 3 °F. We draw on research on numerosity and goal-pursuit from behavioral psychology to explain the intriguingly-opposite findings. We measure both the perceived influence of and actual behavior to help fight climate change. Thus, we offer the novel hypothesis that presenting climate change figures in Celsius or Fahrenheit—two primary units to communicate temperature—can influence people’s belief in or concern regarding climate change.

Große Zahlen beeindrucken halt. Das werden die Öffentlichkeitsstrategen im Potsdamer PIk sicher bald in ihrer tägliche Arbeit umsetzen. Dann heißt es nicht mehr: Der Meeresspiegel steigt pro Jahr um 3 Millimeter an, sondern um 3000 Mikrometer. Und Windgeschwindigkeiten werden dann nicht mehr in km/h angegeben, sondern in cm pro Tag. Da kommen dann schön hohe Werte und viel Klimagrusel heraus. Die Propagandamaschine wird immer perfekter.

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Wieviel Kohlenstoff passt in einen Baum? Seitdem der Planet auf CO2-Diät gesetzt wurde, zählt jetzt jedes Gramm. Das französische landwirtschaftliche Forschungszentrum CIRAD hat nun einen systematischen Rechenfehler gefunden, der alle CO2-Ausgleichmaßnahmen in den Wäldern der Erde beeinflussen wird. In den globalen Bäumen ist 5% weniger Kohlenstoff gebunden als lange angenommmen. CIRAD-Pressemitteilung vom 16. Oktober 2018:

Forest carbon stocks have been overestimated for 50 years

A formula used to calculate basic wood density has recently been corrected. Basic density is widely used to compute carbon storage by trees. Researchers estimate that the error in the initial formula resulted in an overestimation of forest carbon stocks, to the tune of almost 5%. These results were published in the scientific journal American Journal of Botany on 16 October.

It may be a small correction, but it is far from negligible as far as forest ecologists and carbon cycle specialists are concerned. The error lay in a formula established almost 50 years ago (in 1971) for calculating basic wood density. Given that basic density is used to assess the amount of carbon stored in a tree, the fact that the formula had to be corrected meant that forest carbon stocks may have been overestimated by 4 to 5%. “This new formula should enable us to determine more accurately the role of forests in the carbon cycle and the impact of deforestation on climate change” , says Ghislain Vieilledent, an ecologist with CIRAD who was the corresponding author of the work published in the journal American Journal of Botany on 16 October.

For more than 70 years, CIRAD has had a database on 1300 wood species and almost 4500 trees. It was when they came to promote this resource that Ghislain Vieilledent and his colleagues at CIRAD and at Paul Sabatier University in Toulouse discovered an incoherence in a conversion factor: the one used to compute the basic density of a tree based on wood density at 12% moisture, which corresponds to the average wood moisture content in temperate regions. Since this technical characteristic is widely available in wood technology databases, ecologists only have to apply a conversion factor to it in order to establish the basic density of a tree species. However, it was precisely that conversion factor that did not tally with the researchers’ new calculations. “To start with, I thought we had made a mistake in our calculations or that there was some uncertainty surrounding measurement of the relevant data. It was not easy to cast doubt on a formula that had been widely accepted for years and quoted in several scientific articles.”

The researchers took a new look at the data in CIRAD’s historic database in order to determine a new formula for establishing basic density based on density at 12%. The new conversion factor will be used to calculate the basic density of woods in forest ecology databases. In particular, it will serve to update the global wood density database on which Jérôme Chave and Fabian Fischer are working at CNRS-Paul Sabatier University in Toulouse, who were co-authors of the publication. The correction will make it possible to estimate carbon forest stocks more accurately and understand more clearly the role played by forests in climate regulation.