Oceans cover 71% of the Earth’s surface. An analysis of CO2’s radiative effect on ocean temperatures finds CO2 forcing is negligible even after reaching a concentration of 1,071 ppm.
In the tropical oceans, 500 to 1,000 W/m² of solar radiation uniformly heats the first 2 meters of the ocean surface by 2 Kelvin in a span of just 12 hours.
Image Source: Minnett and Kaiser-Weiss (2012) and Fairall et al. (1996)
The solar radiation reaching the Earth’s surface has increased by about 3 W/m² since 1980 (Delgado-Bonal et al, 2020) due to the cloud cover variations that are of “the utmost importance for current climate change” because they “ultimately determine the SW [shortwave] radiation.” This solar radiation increase can explain the recent warming trend.
Image Source: Delgado-Bonal et al, 2020
Oceanographers Wong and Minnett (2018) point out that total CO2 forcing can radiatively exert an impact on only the top 0.01 mm of the ocean’s thermal skin layer. Compare this to 0.09 mm for clouds and 10s of meters for direct solar radiation.
But here is the rub. CO2 must rise to 1,071 ppm (3 x 356.9 ppm) to have a radiative impact that “only gives ~500 mW m−² sr−¹” at the surface. That 500 milliwatts, or 0.5 W/m² sr−¹, is the total impact CO2 can have on the the first 0.01 mm of the global ocean’s thermal skin layer after surpassing 1,000 ppm.
Image Source: Wong and Minnett, 2018
The authors even point out that the greenhouse effect of cloud forcing is 18 times larger (9 W/m² sr−¹) than the forcing associated with a 1,071 ppm CO2 concentration (0.5 W/m² sr−¹) at the ocean surface. So even if CO2 rises by the 1,000s of ppm, the CO2 impact would still not be capable of exceeding the influence of clouds.
Therefore, CO2 cannot be the driver of ocean temperature changes.