“…a distinct pattern of water vapor suppressing the [sea surface temperature] diurnal amplitudes at low latitudes” – Harris et al., 2025

Observations show morning-to-evening sea surface warming amplitudes can exceed 5°C.

Water vapor (WV), the greenhouse gas (GHG) mostly responsible for Earth’s greenhouse effect, adds ~0.1°C warming to this 5°C diurnal change in the high latitude oceans, where WV concentrations are only 100-1000 ppm.

In the tropics, where its concentrations reach 40,000 ppm, the WV contribution to this >5°C diurnal warming is flat (~0.0°C) to negative (a -0.2 to -0.3°C cooling effect).

A 40-fold increase in GHGs/WV can thus can be shown to contribute to cooling the ocean surface instead of enhancing warming.

This is the opposite of what would expected to occur if increasing GHGs were indeed responsible for warming the global oceans.

Image Source: Harris et al., 2025