| Summary: | <p>Aerosol–cloud interactions and their resultant forcing remains one of the largest sources of uncertainty in future climate scenarios. The effective radiative forcing due to aerosol–cloud interactions (ERFaci) is a combination of two different effects, namely how aerosols modify cloud brightness (RFaci, intrinsic) and how cloud extent reacts to aerosol (cloud adjustments CA; extrinsic). Using satellite observations of warm clouds from the NASA A-Train constellation from 2007 to 2010 along with MERRA-2 Reanalysis and aerosol from the SPRINTARS model, we evaluate the ERFaci in warm, marine clouds and its components, the RFaci<sub>warm</sub> and CA<sub>warm</sub>, while accounting for the liquid water path and local environment. We estimate the ERFaci<sub>warm</sub> to be <span tabindex="0" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.32</mn><mo>&#xB1;</mo><mn mathvariant="normal">0.16</mn></mrow></math>">−0.32±0.16</span> Wm<sup>−2</sup>. The RFaci<sub>warm</sub> dominates the ERFaci<sub>warm</sub> contributing 80 % (<span tabindex="0" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.21</mn><mo>&#xB1;</mo><mn mathvariant="normal">0.15</mn></mrow></math>">−0.21±0.15</span> Wm<sup>−2</sup>), while the CA<sub>warm</sub> enhances this cooling by 20 % (<span tabindex="0" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.05</mn><mo>&#xB1;</mo><mn mathvariant="normal">0.03</mn></mrow></math>">−0.05±0.03</span> Wm<sup>−2</sup>). Both the RFaci<sub>warm</sub> and CA<sub>warm</sub> vary in magnitude and sign regionally and can lead to opposite, negating effects under certain environmental conditions. Without considering the two terms separately and without constraining cloud–environment interactions, weak regional ERFaci<sub>warm</sub> signals may be erroneously attributed to a damped susceptibility to aerosol.</p>
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