An unheralded 2025 study used long-term, observed cloud-cover data over oceans to identify trends in radiative fluxes from 1900 to 2020. 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. [some emphasis, links added]
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 last 120 years, 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 a decreasing trend of -0.5 W/m² per decade since 1900, and even a slight decline in the radiation balance (-0.18 W/m² per decade) during the same 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 the past 50 years.
This does not support the contention that CO2 is a driver – let alone a significant contributor – to the radiative fluxes that affect ocean heat content.
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