Clouds have the capacity to dramatically influence climate changes in both radiative longwave (the “greenhouse effect”) and shortwave.
Cloud cover domination in longwave radiation
In the longwave, clouds thoroughly dwarf the CO2 climate influence. According to Wong and Minnett (2018):
• The signal in incoming longwave is 200 W/m² for clouds over the course of hours. The signal amounts to 3.7 W/m² for doubled CO2 (560 ppm) after hundreds of years.
• At the ocean surface, clouds generate a radiative signal 8 times greater than tripled CO2 (1120 ppm).
• The absorbed surface radiation for clouds is ~9 W/m². It’s only 0.5 W/m² for tripled CO2 (1120 ppm).
• CO2 can only have an effect on the first 0.01 mm of the ocean. Cloud longwave forcing penetrates 9 times deeper, about 0.09 mm.
Cloud cover domination in shortwave radiation
In its shortwave albedo capacity, cloud cover modulates the amount of solar radiation that warms the ocean. Changes in the Earth’s radiation budget “are caused by changes in tropical mean cloudiness.” (Wielicki et al., 2002).
When cloud cover increases, less shortwave radiation reaches the surface, leading to cooling. When cloud cover decreases – as it has since the 1980s – more solar radiation is absorbed.
The decrease in cloud cover in recent decades can therefore explain the 1979-2017 warming (Herman et al., 2013, Poprovsky, 2019, Loeb et al., 2018).
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