Cloud Radiative Effect Variability in the Recent Satellite Record and Associated Cloud Feedback

Abstract

We investigate changes in the shortwave (SW) and longwave (LW) cloud radiative effect (CRE) as inferred by 20+years of measurements by NASA’s CERES and MODIS instruments, and attempt to distinguish and quantify the contributions of radiative flux anomalies due to cloud and non-cloud changes. The flux anomalies due to presumed cloud changes, collectively termed “cloud feedback” or “cloud radiative response” are examined under both the cloud radiative kernel (CRK) and the “adjusted CRE” frameworks. We compare CRK’s standard estimate of cloud varying kernels operating on observed monthly 1° cloud anomalies resolved by cloud type. We show that temporally varying kernels from satellite observations enable reconstruction of observed SW and LW CRE trends. Decomposition indicates that the contribution to the LW CRE trend from kernel variations, not accounted by time-invariant kernels, exceeds the contribution from changes in cloud type amounts. This suggests that CRE trends are strongly affected by changes in the sensitivity of radiation under fixed cloud types, which has been hitherto unaccounted for. When comparing CRK-based cloud feedback with that from the so called “adjusted CRE” method we find broad agreement in their geographical patterns which resemble those of CRE. Global-mean values are however different due to either unaccounted cloud feedback in the former method and/or imperfect cloud masking corrections in the latter method. While the global time series and geographical patterns of CRE anomalies and cloud feedback generally track each other, CRK-based LW cloud feedback differs from CRE anomaly trends by about 0.5 Wm⁻²decade⁻¹ 34 , presumably due to non-cloud effects and/or unaccounted cloud feedback.