Überhöhte Temperaturen: Bahnveränderungen von Satelliten verfälschen Messwerte

Bionahrung ist gesund. Aber profitiert auch die Umwelt davon? Eine Studie von Eva-Marie Meemken und Matin Qaim im Annual Review of Resource Economics lässt Zweifel aufkommen. Der geringere Ertrag gefährdet die Umwelt durch Flächenfrass und die höheren Kosten führen zu Hunger bei den ärmeren Schichten:

Organic Agriculture, Food Security, and the Environment
Organic agriculture is often perceived as more sustainable than conventional farming. We review the literature on this topic from a global perspective. In terms of environmental and climate change effects, organic farming is less polluting than conventional farming when measured per unit of land but not when measured per unit of output. Organic farming, which currently accounts for only 1% of global agricultural land, is lower yielding on average. Due to higher knowledge requirements, observed yield gaps might further increase if a larger number of farmers would switch to organic practices. Widespread upscaling of organic agriculture would cause additional loss of natural habitats and also entail output price increases, making food less affordable for poor consumers in developing countries. Organic farming is not the paradigm for sustainable agriculture and food security, but smart combinations of organic and conventional methods could contribute toward sustainable productivity increases in global agriculture.

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Früher war man bei der Temperaturmessung auf Bodenmessstationen angewiesen, die aber nur lückenhaft die Erde abdeckten. Heute kreisen Satelliten um die Erde, die auf indirektem Wege die Temperatur der unteren Atmosphäre messen. Das ist nicht immer unproblematisch, insbesondere wenn sich im Laufe der Zeit die Bahn der Satelliten verändert. Christy et al. 2018 haben nun errechnet, dass durch Bahn- und Sensorveränderungen die Messergebnisse der Satelliten verfälscht werden, wobei zusätzliche Wärme vorgegaukelt wird, die in der Realität gar nicht existiert. Hier der Abstract der Studie, die am 8. März 2018 im International Journal of Remote Sensing erschien:

Examination of space-based bulk atmospheric temperatures used in climate research
The Intergovernmental Panel on Climate Change Assessment Report 5 (IPCC AR5, 2013) discussed bulk atmospheric temperatures as indicators of climate variability and change. We examine four satellite datasets producing bulk tropospheric temperatures, based on microwave sounding units (MSUs), all updated since IPCC AR5. All datasets produce high correlations of anomalies versus independent observations from radiosondes (balloons), but differ somewhat in the metric of most interest, the linear trend beginning in 1979. The trend is an indicator of the response of the climate system to rising greenhouse gas concentrations and other forcings, and so is critical to understanding the climate. The satellite results indicate a range of near-global (+0.07 to +0.13°C decade−1) and tropical (+0.08 to +0.17°C decade−1) trends (1979–2016), and suggestions are presented to account for these differences. We show evidence that MSUs on National Oceanic and Atmospheric Administration’s satellites (NOAA-12 and −14, 1990–2001+) contain spurious warming, especially noticeable in three of the four satellite datasets. Comparisons with radiosonde datasets independently adjusted for inhomogeneities and Reanalyses suggest the actual tropical (20°S-20°N) trend is +0.10 ± 0.03°C decade−1. This tropical result is over a factor of two less than the trend projected from the average of the IPCC climate model simulations for this same period (+0.27°C decade−1).

Die dazugehörige Pressemitteilung zur Studie finden Sie hier.