7. Conclusions
The relationship between atmospheric concentration of carbon dioxide and the global temperature is widely recognized and it is common knowledge that increasing CO2 concentration plays a major role in enhancement of the greenhouse effect and contributes to global warming.
While the fact that these two variables are tightly connected is beyond doubt, the direction of the causal relationship needs to be studied further. The purpose of this study is to complement the conventional and established theory that increased CO2 concentration due to anthropogenic emissions causes an increase of temperature, by considering the concept of reverse causality. The problem is obviously more complex than that of exclusive roles of cause and effect, qualifying as a “hen-or-egg” (“ὄρνις ἢ ᾠὸν”) causality problem, where it is not always clear which of two interrelated events is the cause and which the effect. Increased temperature causes an increase in CO2 concentration and hence we propose the formulation of the entire process in terms of a “hen-or-egg” causality.
We examine the relationship of global temperature and atmospheric carbon dioxide concentration using the most reliable global data that are available—the data gathered from several sources, covering the common time interval 1980–2019, available at the monthly time step.
The results of the study support the hypothesis that both causality directions exist, with T → CO2 being the dominant, despite the fact that the former CO2 → T prevails in public, as well as in scientific, perception. Indeed, our results show that changes in CO2 follow changes in T by about six months on a monthly scale, or about one year on an annual scale.
The opposite causality direction opens a nurturing interpretation question. We attempted to interpret this mechanism by noting that the increase of soil respiration, reflecting the fact that the intensity of biochemical process increases with temperature, leads to increasing natural CO2 emission. Thus, the synchrony of rising temperature and CO2 creates a positive feedback loop. This poses challenging scientific questions of interpretation and modelling for further studies. In our opinion, scientists of the 21st century should have been familiar with unanswered scientific questions, as well as with the idea that complex systems resist simplistic explanations.
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