Atmospheric Temperature and CO2: Hen-Or-Egg Causality?

Abstract

It is common knowledge that increasing CO2 concentration plays a major role in enhancement of the greenhouse effect and contributes to global warming. The purpose of this study is to complement the conventional and established theory, that increased CO2 concentration due to human emissions causes an increase in temperature, by considering the reverse causality. Since increased temperature causes an increase in CO2 concentration, the relationship of atmospheric CO2 and temperature may qualify as belonging to the category of “hen-or-egg” problems, where it is not always clear which of two interrelated events is the cause and which the effect. We examine the relationship of global temperature and atmospheric carbon dioxide concentration in monthly time steps, covering the time interval 1980–2019 during which reliable instrumental measurements are available. While both causality directions exist, the results of our study support the hypothesis that the dominant direction is T → CO2. Changes in CO2 follow changes in T by about six months on a monthly scale, or about one year on an annual scale. We attempt to interpret this mechanism by involving biochemical reactions as at higher temperatures, soil respiration and, hence, CO2 emissions, are increasing.

On Spurious Causality, CO2, and Global Temperature

“…As it turns out, considering this less contentious CO 2 series does not resolve the apparently counterintuitive finding that GMTA explains a larger portion of the forecast error variance of CO 2 than vice versa. Such a finding has also been reported using a different methodology in Koutsoyiannis and Kundzewicz (2020). We explore a last avenue, that of using annual CO 2 emissions rather than RF CO 2 t .…”

Rethinking Climate, Climate Change, and Their Relationship with Water

“…According to Kuhn et al [47], four billion years ago the solar irradiance was about 80% of the current value (or, according to other estimates, 75%), the Earth's rotation rate was 170% of the current, the land area was very small, less than 4% of the current value, and the atmospheric CO 2 concentration was about three orders of magnitude higher or more (up to 250,000%; see this information in a combined graph in [48]). Note that even in the Cenozoic (the last 65 million years) the atmospheric CO 2 concentration varied by more than two orders of magnitude (see graph in [49]). Amazingly however, despite these cosmogonic changes, the temperature remained fairly constant (varying by only 10%, which is equivalent to 29 K) during all these four billion years.…”

“…The importance of the effect of the different greenhouse gases, or other agents affecting climate, is not necessarily related to the research efforts and scientific publications on each of them. Arguably, the fact that the CO 2 has been so heavily and repeatedly studied, particularly in paleoclimatology studies (e.g., [49,[51][52][53][54][55][56][57]), does not suggest that it is more important a greenhouse gas than water. A simpler explanation is that CO 2 concentration is easier to study because its change in time is smoother, because its spatial heterogeneity is much lower than that of water vapour, and because it can be detected in ice and sediment cores, stomatal complexes, etc.…”

“…To this physical process we should add the fact that increase of temperature (T) results in increased respiration of the biosphere on land and sea. Based on such considerations, and using reliable instrumental measurements of global T and CO 2 concentration covering the time interval 1980-2019, a recent study [49] found that in the relationship of CO 2 and temperature, the dominant causality direction is T → CO 2 , rather than the other way round, despite the latter being the common perception.…”

Rethinking Climate, Climate Change, and Their Relationship With Water

“…To this natural process we should add the fact that the increase of temperature (T) results in increased respiration of the biosphere on land and sea. Based on such considerations and using reliable instrumental measurements of global T and CO2 concentration, covering the time interval 1980-2019, a recent study [50] has found that, in the relationship of CO2 and temperature, the dominant causality direction is T → CO2, rather than the other way round, despite the latter being the common perception.…”