Since the discovery of the phenomenon of abnormal cooling and sinking of the middle and upper atmosphere in 1993–1998, two concepts have developed which explain its origin by man-made processes. Both focus on different consequences arising from one common cause — the burning of carbon fuels on an industrial scale. The first concept is based on the hypothesis about the key role of the decrease in oxygen content in the atmosphere in this process. The second model, which emerged a little later, attributes the observed effects to the growth of greenhouse gases in the atmosphere, primarily CO2. Over the years, numerous attempts have been made to confirm the assumption of the dominance of the second mechanism in the excitation of the long-term trend of the climate of the middle and upper atmosphere. However, all of them turned out to be futile. At the same time, today, firstly, the validity of the first proposed hypothesis is justified which recognizes the leading role of oxygen in climate change in the upper atmosphere, and secondly, errors that cause the erroneous rejection of this conclusion are revealed. It becomes obvious that man-made processes affecting the atmosphere lead to two multidirectional phenomena: a) global warming of the troposphere; b) global cooling of the thermosphere: an extreme increase in the mass of CO2 heats the lower layers of the atmosphere, and its upper layers are cooled even by an inconspicuous decrease in part of O2 relative to the total mass. Since nothing indicates a decline in the man-made activity of the world civilization in the coming years, in order to adequately predict the consequences of an increase in atmospheric pollution the effect of a decrease in oxygen content on the state of near-Earth outer space should probably be taken into account.