No Anthropogenic Climate Change? Another case where correlation is falsely interpreted to indicate causality
Lauantai 20.7.2019 klo 15:05 - Mikko Nikinmaa
An article “giving experimental evidence” that it is not greenhouse gases, but changes in humidity/low level clouds, causing temperature increase, is circulating. The article is widely used by climate sceptics to indicate that carbon dioxide increase has little to do with the observed temperature increase. I wish it were so, but a quick reading of the ArXiv 2019 (Kauppinen & Malmi; arxiv.com) manuscript (NO EXPERIMENTAL EVIDENCE FOR THE SIGNIFICANT ANTHROPOGENIC CLIMATE CHANGE) indicates a serious problem in the conclusion. Measurements of temperature change are unequivocal – temperature has increased markedly from preindustrial time, especially during the last 50 years. Since temperature, cloud cover and humidity data can be found, the authors have calculated correlations between temperature and the other two and have shown significant relationship. Up to this point I have no quarrel with the authors. But then, at least to my understanding, they conclude that these correlations indicate causality. From the observed temperature and cloud cover change they calculate that an increase in % cloud cover causes a decrease in temperature by 0.11 degrees/% cloud cover. However, correlation does not mean causality, it is equally possible that an additional factor influences one or both components of the correlation. A good example of this is the classical ice cream eating and drowning-relationship. There is very tight correlation between the consumption of ice cream and the number of drowning accidents. Yet, few people would claim that ice cream eating causes drowning. A similar problem is in this case, the authors’ calculation indicates an association between cloud cover change and temperature increase. However, the reason why the temperature increases is not verified by the authors’ calculations. It could be anything, for example anthropogenic. Thus, the study does not prove “that the changes in the low cloud cover fraction practically control the global temperature”. It is difficult for me to understand, why this kind of obvious weakness has remained unobserved, when at the same time inaccuracies in the IPCC conclusions are pointed out.