Comment on "Long-term climate forcing by atmospheric oxygen concentrations".

Area of Science:

• Earth Science
• Paleoclimatology
• Atmospheric Science

Background:

• Poulsen et al. proposed that reduced Phanerozoic atmospheric oxygen levels would lead to a warmer climate.
• This hypothesis contrasts with established principles where lower pressure and altered radiative transfer typically induce cooling.

Purpose of the Study:

• To re-evaluate the relationship between atmospheric oxygen levels and global climate during the Phanerozoic.
• To investigate the discrepancies between proposed warming and expected cooling effects.

Main Methods:

• Analysis of radiative transfer processes within climate models.
• Examination of atmospheric structure changes under varying pressure conditions.
• Comparison of model outputs to identify inconsistencies.

Main Results:

• Lower atmospheric pressure, associated with reduced oxygen, induces cooling effects.
• Radiative transfer changes under lower pressure also contribute to a cooling climate.
• Existing climate models present conflicting results regarding oxygen levels and temperature.

Conclusions:

• The assertion that lower Phanerozoic oxygen levels caused warming requires further scrutiny.
• A detailed mechanistic explanation for the observed model conflicts is needed.
• Further research should focus on the representation of radiative and cloud processes in climate models.