The data show flat trends in shortwave radiation, longwave radiation, and radiation balance for the global ocean since 1970 despite a 100 ppm increase in CO2.

An unheralded 2025 study  uses long-term observed cloud cover data over oceans to uncover trends in radiative fluxes from 1900 to 2020.

Trends in the subtropics (15-40°N, 45-65°W) indicate a +1 W/m² per decade increase in both shortwave (SW) radiation and radiation balance over the 120-year period, amounting to 13 W/m² in overall ocean heat gains that were not offset by modest trends in longwave (LW) radiation.

On the other hand, the SW radiation fluxes over mid-latitude oceans (40-50°N, 10-30°W) indicate -0.5 W/m² per decade decreasing trends since 1900, and even a slight decline in radiation balance (-0.18 W/m² per decade) during this period.

Interestingly, the global ocean radiation data indicate there have been no obvious trends in SW, LW, or radiation balance since about 1970 despite the nearly 100 ppm rise in CO2 concentration (from 325 to 420 ppm) over this 50-year period.

This does not support the contention that CO2 is a driver – let alone a significant contributor – to the radiative fluxes affecting ocean heat content.

Image Source: Aleksandrova and Golev, 2025