Response to R. I. Holmes on Total Solar Irradiance and Temperature at 1 Bar


This work responds to Holmes (2019) in Earth Sciences 8.6, DOI: 10.11648/, which suggests that the temperatures of terrestrial planets with thick atmospheres depend primarily on total solar irradiance and pressure, based on examination of Venus, Earth, and Titan at an altitude where the pressure is 1 bar.

A re-evaluation of the data invalidates the hypothesis in the case of Titan. Calculating a temperature for Earth based on Titan data yields a temperature for Earth that is too low by 25-30 K. The proposed numerical relationship is confirmed to exist between data for Venus and Earth, within a narrow range of pressures.

However, there is no indication that this single-data-point correlation is associated with causation. To the contrary, the hypothesis is non-physical, in that it postulates that solar energy reflected away from a planet influences planetary temperature just as much as solar energy that is absorbed by the planet.

Holmes had suggested that it would be difficult for explanations in terms of albedo and the greenhouse effect to account for the numerical coincidence, given that the albedo and greenhouse gas characteristics of the two planets are very different. However, an analysis in terms of the albedo and greenhouse effect of each planet was found to be fully consistent with the empirical relationship between the temperatures of Venus and Earth at 1 atm.

A separate analysis was offered to show that percent greenhouse gases is a meaningless metric for predicting the relative size of the greenhouse effect on different planets; an improved metric was offered.

No statistical or physical basis was found for believing the relationship identified by Holmes is general or reflects a causal relationship. No justification was found to interpret the single-data-point relationship between the temperatures of Venus and Earth as anything other than a coincidence.

Full Paper

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Publication history: Released January 2, 2024. Any revisions will be posted to this page.

Figure 2: Temperature profiles of Venus and Earth [Figure 2 from F. Taylor and D. Grinspoon. “Climate evolution of Venus”. In: J. Geophys. Res. 114.E9 (2009). doi: 10.1029/2008JE003316]