The decline of global atmospheric oxygen over 1990-2005 calls for attention

The rapid increase of the atmospheric carbon dioxide (CO 2 ) and its great impact on global climate since the industrial revolution has drawn much attention of the science community, while the change of oxygen (O 2 ) has been concerned only in the recent decades and mainly in oceanic regions. It has been observed that oxygen concentration has decreased in the open ocean thermocline in many ocean regions since 1960s. Warming-induced stratification leads to the decline of the supply of oxygen to thermocline from the near surface waters. As the second-most abundant component in the atmosphere (following nitrogen) and the most important component supporting lives, O 2 constitutes 21% of the earth’s atmosphere and is often regarded as being virtually inexhaustible. However, observational data from the Scripps O 2 Program shows a downward trend of 4 ppm per year since the late 1980s, approximately twice the upward trend of CO 2 . What has caused the decline in atmospheric O2 at the global scale? To what extent will the O2 concentration drop in the future? Will it affect the human health? These are all pressing problems.