The fraction of cloud water compared to its adiabatic value is defined as the adiabatic fraction, fad. The accuracy of cloud representation in climate models is highly sensitive to mixing rate, manifested in fad. Here, we present the first fad distribution of marine boundary layer clouds over global oceans, retrieved by satellite observations. The fad is shown to decrease exponentially with cloud base temperature (CBT) and cloud depth, in agreement with the increasing evaporation capacity of entrained warmer air. Cloud cover decreases with increasing CBT, but to a much lesser extent than fad. The dependence of fad on CBT has little dependence on relative humidity or precipitation. The relationship between CBT and fad highlights the importance of CBT as a core control factor on cloud evaporation. The simultaneous decrease in cloud water content and cover with increasing CBT can lead to positive cloud feedback, resulting in greater future climate warming. Plain Language Summary: Clouds lose water through evaporation and precipitation. The cloud adiabatic fraction (fad) represents the degree of cloud mixing with the surrounding air. A smaller fad corresponds to a stronger atmospheric mixing, which leads to a decrease in the amount of cloud water and coverage, thereby resulting in less solar radiation being reflected back to space. This contributes to climate warming. Studies on fad mostly rely on limited ground‐based or aircraft observations, leaving much unknown about its effects in cloud physics studies. In this study, we present the first‐ever global climatology fad distribution for water boundary layer clouds over global oceans. Using this global‐scale fad data, we found that cloud base temperature (CBT) has the most significant impact on fad, while lower tropospheric stability and precipitation have minor effects. As CBT increases, the fad and cloud cover decrease. Additionally, fad decreases with increasing cloud depth because the mixing with ambient air accumulates with height above the cloud base. The decrease in fad, cloud water, and cover with increasing CBT can result in positive cloud feedback, further emphasizing clouds' role in climate warming. Key Points: The first‐ever global climatology of cloud adiabatic fraction of marine boundary layer clouds was retrieved by satellite observationsCloud base temperature and cloud depth dominate the variation of the cloud adiabatic fractionCloud adiabatic fraction is positively correlated with cloud cover [ABSTRACT FROM AUTHOR]